Effects of anthropogenic underwater noise on harbour

University of Veterinary Medicine Hannover, Foundation

Effect of anthropogenic underwater noise on harbour

porpoise hearing in areas of high ecological importance

Einfluss anthropogener Schalleinträge auf das Gehör von Schweinswalen in Gebieten

von hoher ökologischer Bedeutung

INAUGURAL - DISSERTATION

submitted in fulfilment of the requirements for the degree

- Doctor rerum naturalium -

(Dr. rer. nat.)

submitted by

Tobias Schaffeld

Kamp-Lintfort

Büsum 2020

Scientific supervision: Prof. Prof. h. c. Dr. Ursula Siebert

Institute for Terrestrial and Aquatic Wildlife Research,

University of Veterinary Medicine Hannover, Foundation.

Prof. Dr. Felix Felmy

Institute of Zoology,


First supervisors: Prof. Prof. h. c. Dr. Ursula Siebert



Prof. Dr. Felix Felmy

Institute of Zoology,


Second supervisor: Prof. emeritus Dr. Paul Nachtigall

Institute of Marine Biology,

University of Hawaii, Kailua Hawaii.

Date of oral examination: 13.05.2020

Parts of this study were published in peer-reviewed journals:

Schaffeld, T., Schnitzler, J.G., Ruser, A., Woelfing, B., Baltzer, J., Siebert, U. (2020). Effects

of multiple exposure to pile driving noise on harbor porpoise hearing during

simulated flights – an evaluation tool. Journal of the Acoustical Society of America,

Volume 147, Issue 2, 685-697, doi: 10.1121/10.0000595.

Schaffeld, T., Ruser, A., Woelfing, B., Baltzer, J., Kristensen, J.H., Larsson, J., Schnitzler,

J.G., Siebert, U. (2019). The use of seal scarers as a protective mitigation measure can

induce hearing impairment in harbour porpoises Journal of the Acoustical Society of

America, Volume 146, Issue 6, 4288-4298, doi: 10.1121/1.5135303.

Parts of this study are in preparation for a publication in a peer-reviewed journal:

Schaffeld, T., Schnitzler, J.G., Ruser, A., Woelfing, B., Baltzer, J., Fischer, M., Schuster, M.,

Siebert, U. (2020). Acoustic water velocity measurements in rivers can affect harbour

porpoise hearing.

Results of this study were published in reports:

Ruser, A., Baltzer, J., Schaffeld, T., Woelfing, B., Schnitzler, J.G, Siebert, U. (2019).

Auswirkungen des Unterwasserschalls der Offshore-Windenergieanlagen auf

marine Säugetiere – Unterwasserschall Effekte (UWE). Final Report on behalf of the

Federal Agency for Nature Conservation. Project title: Effects of underwater noise of

offshore-wind farms on marine mammals. Project no. FKZ 3515 82 200.

Schaffeld, T., Ruser, A., Schnitzler, J.G., Baltzer, J., Siebert, U. (2018). Bewertung von

Auswirkungen von Unterwasserschallemissionen auf Schweinswale (Phocoena

phocoena). Report on behalf of the Hamburg Port Authority.

Results of this study were presented on the following conferences:

Schaffeld, T., Ruser, A., Schnitzler, J.G., Woelfing, B., Baltzer, J., Siebert, U. (2018). Hazard

zones for potential auditory damage – Estimated cumulative effects of pile driving

for harbour porpoises in the German North Sea (Poster). In abstract book page 48. 6th

International meeting on the Effects of Sound in the Ocean on Marine Mammals, The

Hague, Netherlands, 9th – 14th of September 2018.

Schaffeld, T., Ruser, A., Schnitzler, J.G., Woelfing, B., Baltzer, J., Siebert, U. (2019). Effects

of multiple exposure to pile driving noise on harbour porpoise hearing during

simulated flights – a risk evaluation tool (Poster and Talk). In abstract book page 163.

The Effects of Noise on Aquatic Life, The Hague, Netherlands, 7th – 12th of July 2019.

Awarded with the 2nd prize of the Rodney Coates award for the best student presentation.

Schaffeld, T., Ruser, A., Schnitzler, J.G., Woelfing, B., Baltzer, J., Siebert, U. (2019). Acoustic

harassment devices (seal scarers) can affect harbour porpoise hearing temporarily

(Talk). In abstract book page 634-635. World Marine Mammal Conference, Barcelona,

Spain, 9th – 12th of December 2019.

Table of Contents

Table of contents

List of abbreviations .......................................................................................................................... I

Introduction ...................................................................................................................................... 1

I. Echolocation ....................................................................................................................................... 1

II. Hearing adaptations ............................................................................................................................ 3

III. Communication ................................................................................................................................... 4

IV. Determination of hearing thresholds ................................................................................................... 6

V. Effects of anthropogenic underwater noise pollution ......................................................................... 7

VI. Protective regulations for harbour porpoises .................................................................................... 10

VII. Motivation ......................................................................................................................................... 12

Effects of multiple exposure to pile driving noise on harbor porpoise hearing during

simulated flights – an evaluation tool. .................................................................................. 14

Chapter 1: Effects of multiple exposure to pile driving noise on harbor porpoise hearing

during simulated flights – an evaluation tool ....................................................................... 15

Abstract ...................................................................................................................................................... 15

Author contributions .................................................................................................................................. 16

I. Introduction ....................................................................................................................................... 17

II. Material & Methods .......................................................................................................................... 20 A. Study site and pile driving recordings ......................................................................................................... 20 B. Sound propagation modelling and frequency analysis ................................................................................ 21 C. Model assumptions ...................................................................................................................................... 23 D. Estimation of hazard zones .......................................................................................................................... 25

III. Results ............................................................................................................................................... 26 A. Sound propagation in the study area ............................................................................................................ 26 B. Estimation of hazard zones .......................................................................................................................... 28

IV. Discussion ......................................................................................................................................... 33 A. Simulation results ........................................................................................................................................ 33 B. Application of evaluation tool ..................................................................................................................... 36 C. Ecological relevance of disturbance ............................................................................................................ 39 D. Conclusion ................................................................................................................................................... 41 E. Acknowledgement ....................................................................................................................................... 41 F. APPENDIX ................................................................................................................................................. 42

The use of seal scarers as a protective mitigation measure can induce hearing impairment in

harbour porpoises. ................................................................................................................. 44

Chapter 2: The use of seal scarers as a protective mitigation measure can induce hearing

impairment in harbour porpoises ......................................................................................... 45

Abstract ...................................................................................................................................................... 45


I. Introduction ....................................................................................................................................... 47

Table of Contents

II. Material & Methods .......................................................................................................................... 49 A. Study area and animal subject ..................................................................................................................... 49 B. Background noise recordings ...................................................................................................................... 49 C. Experimental procedure to measure hearing thresholds .............................................................................. 50 D. Fatiguing stimulus and experimental procedure .......................................................................................... 52 E. TTS definition ............................................................................................................................................. 55 F. Data analysis ................................................................................................................................................ 56

III. Results ............................................................................................................................................... 58 A. Baseline hearing thresholds ......................................................................................................................... 58 B. Post-exposure thresholds ............................................................................................................................. 58

IV. Discussion ......................................................................................................................................... 60 A. Application of Seal Scarers ......................................................................................................................... 60 B. Effect on harbour porpoise hearing ............................................................................................................. 61 C. Estimated hazard zones ............................................................................................................................... 63 D. Cumulative effects of multiple exposure ..................................................................................................... 64 E. Management approach ................................................................................................................................. 65 F. Conclusion ................................................................................................................................................... 66

V. Acknowledgement ............................................................................................................................ 67

VI. Appendix ........................................................................................................................................... 68

Ultrasonic aqua flowmeters in rivers affect harbour porpoise hearing .................................... 72

Chapter 3: Ultrasonic aqua flowmeters in rivers affect harbour porpoise hearing ................ 73

Abstract ...................................................................................................................................................... 73


I. Introduction ....................................................................................................................................... 75 A. Study area and underwater noise measurements ......................................................................................... 77 B. Sound propagation model ............................................................................................................................ 79 C. Effect of 28 kHz fatiguing sound on harbour porpoise hearing ................................................................... 81 D. Simulation of harbour porpoise migration through acoustic field ............................................................... 82 E. Evaluation of potential to induce a TTS ...................................................................................................... 83

II. Results ............................................................................................................................................... 85 A. Baseline hearing thresholds ......................................................................................................................... 85 B. Post-exposure thresholds ............................................................................................................................. 85 C. TTS potential of flowmeter for single pulses .............................................................................................. 85 D. Received levels on simulated flights ........................................................................................................... 87 E. TTS potential for harbour porpoise which stay around the flowmeters....................................................... 89

III. Discussion ......................................................................................................................................... 90 A. Evaluation of potential effects of the flowmeter on harbour porpoise hearing ............................................ 90 B. Effects on behaviour .................................................................................................................................... 91 C. Management approach ................................................................................................................................. 91

IV. Acknowledgement ............................................................................................................................ 92

Conclusion ....................................................................................................................................... 93

I. Evolution of noise mitigation ............................................................................................................ 93 A. Unintended effects of underwater sound application................................................................................... 95 B. Naive implementation of underwater sounds .............................................................................................. 97 C. Established concept for noise mitigation ..................................................................................................... 98

II. Outlook ........................................................................................................................................... 100

Table of Contents

A. Acoustic flowmeter ................................................................................................................................... 100 B. Acoustic deterrent devices ......................................................................................................................... 101

III. Future directions of TTS research ................................................................................................... 101 A. Biological mitigation as a regulation approach ......................................................................................... 101 B. Understanding of TTS ............................................................................................................................... 102 C. Ecological relevance of temporary threshold shifts ................................................................................... 103

Summary ....................................................................................................................................... 107

Zusammenfassung ........................................................................................................................ 110

Bibliography ................................................................................................................................. 113

List of figures ................................................................................................................................ 133

List of tables .................................................................................................................................. 134

Acknowledgement ........................................................................................................................ 135

Declaration of Originality ............................................................................................................ 136

Curriculum vitae .......................................................................................................................... 137

List of abbreviations

I

List of abbreviations

In addition to the commonly used abbreviations following short forms were used:

ABR Auditory Brainstem Response

ADD Acoustic Deterrent Device

AEP Auditory Evoked Potential

AFM Acoustic Flowmeter

ITAW Institute for Terrestrial and Aquatic Wildlife Research

MDD Minimum Deterrence Distance

MSFD Marine Strategy Framework Directive

OWF Offshore wind farm

PTS Permanent Threshold Shift

SEL Sound Exposure Level (in dB re 1 µPa²s)

SELSS Sound Exposure Level of Single Strike (in dB re 1 µPa²s)

SELcum Cumulative Sound Exposure Level (in dB re 1 µPa²s)

SEL-TTSonset Minimum SEL to induce a significant temporary threshold shift

SHEQ Still Higher than Effective Quiet

SPL Sound Pressure Level (in dB re 1 µPa)

TTS Temporary Threshold Shift

II

Introduction

1

Introduction

I. Echolocation

Among marine mammals, toothed whales (Odontocetes) have extraordinarily adapted to an

environment with limited vision ranges (Fenton et al., 2014). Similar to bats, toothed whales

gain further sensory input in addition to visual and positional sensors by emitting brief acoustic

pulses (clicks) and waiting for returning echoes (Fenton et al., 2014). These echoes carry

information, encoded in the time difference between pulse and echo as same as acoustic

characteristics, to generate an auditory image of their environment (Fenton et al., 2014). This

process is called echolocation. Finding and catching prey items independent from vision

represents a huge evolutionary advantage, which enables toothed whales to occupy habitats

with limited visibility (Fenton et al., 2014). The ability to echolocate characterises the 72

odontocete species, which occur in all marine habitats from deep pelagic zones to rivers (Fenton

et al., 2014; McGowen et al., 2009). The key for this acoustic perception of the environment

was the evolution of a highly specialized nasal sound production system (e.g. Huggenberger et

al., 2009; Madsen et al., 2002). An important development in this context was the resettlement

of the blowhole to the top of the head, which enables to breathe easily at the surface. This was

achieved by a migration of the nasal passages up to a dorsal location, separating from the

esophagus (Fenton et al., 2014). In most tooth whale species, echolocation clicks are generated

by phonic lips, which are located in the upper nasal passages (Cranford et al., 1996; Madsen et

al., 2003). This tissue complex consists of a variety of diverticula and a pair of fatty bursae,

which is embedded in a pair of connective tissue lips (Cranford et al., 1996). This highly

specialized adaptation represents a major advantage compared to echolocating bats, which

spent two to five times more energy when producing calls by the larynx (Dechmann et al.,

2013). Odontocetes however, produce echolocation clicks by forcing pressurised air through

the phonic lips (Ridgway and Carder, 1988). The energetic costs to produce clicks are assumed

to be negligible, since even deep-diving pilot whales require very small amounts of of air per

click (50-100 µL,) which are recycled again between the nasal sacs (Foskolos et al., 2019). The

clicks are emitted in a narrow beam of high intensity after being filtered and collimated by the

concave upper surface of the skull, underlying air sacs and a fatty melon in the forehead (Aroyan

et al., 2000). Among the highly specialised members of the Odontocetes, the sperm whale

evolved an outstanding melon, accounting for about one-third of its total body length (e.g.

Introduction

2

Madsen et al., 2002). Moreover, the clicks travel from the phonic lips positioned at the anterior

end of the melon back through the melon towards the frontal air sacs, where they are reflected

and from where they travel through the junk into the environment (Madsen et al., 2002; Møhl

et al., 2003; Zimmer et al., 2005). This mechanism enables the sperm whale to produce a

narrow, forward-directed and high intense sonar beam, exceeding 236 dB re 1 µPa (Møhl et al.,

2003). This represents the highest biological sound level known.

The ability to produce high amplitude echolocation clicks is substantial to explore the occupied

large water bodies by long-range echolocation (Møhl et al., 2003). The detection range of

toothed whales is positively correlated with body size, as the transmitted acoustic power is

dependent on the size of the vibrating phonic lips and the involved muscles when generating

air pressure (Jensen et al., 2018; Ridgway and Carder, 1988). The vocalization frequency of

terrestrial animals is negatively correlated with body size (Bradbury and Vehrencamp, 2011),

which has been confirmed for toothed whales also (Jensen et al., 2018). The directivity index,

as an indicator for the perceived acoustic field, was shown to be almost the same for a variety

of tested toothed whales with weights between 50 and 30000 kg (Jensen et al., 2018). The

product of melon size as the acoustic transmitter and the frequency of produced echolocation

signals determines directivity (Jakobsen et al., 2013). Accordingly, in order to maintain a

narrow field of view, the harbour porpoise must produce clicks of higher frequency than the

sperm whale, since the melon size is much smaller (Jakobsen et al., 2013; Jensen et al., 2018).

The echolocation clicks of harbour porpoises are emitted in a highly directive beam of 11-13°

(Koblitz et al., 2012), which is half as wide as the receiving system (Kastelein et al., 2005). A

narrow acoustic field of view provides evolutionary benefits such as a larger detection range.

Echolocation clicks can travel further distances, when the acoustic field is focused, allowing

for a detection of prey patches at further distances (Au, 2014). At the same time, unwanted

echoes are also reduced by this spatial filtering, which is highly beneficial when operating in

acoustically complex habitats like a coastal environment (Dukas, 2004; Jensen et al., 2018).

The optimal-localization hypothesis furthermore describes, that a narrow acoustic field is

supportive in localizing prey (Yovel et al., 2010). The detection and localization of prey are

two different mechanisms, which compromise each other. The detection of targets is most

efficiently in the center of the echolocation beam, because returning echoes contain highest

intensity. The localization of targets is more precise, when the target is pointed off axis, at the

Introduction

3

point with the highest slope of the beam (Yovel et al., 2010). Harbour porpoises produce

echolocation clicks with a bandwidth of 6 – 26 kHz, which are centered between 130 and

140 kHz (Møhl and Andersen, 1973; Villadsgaard et al., 2007). These high frequency clicks

have a wavelength of slightly more than 1 cm, which enables to recognize small targets of

similar size (Miller and Wahlberg, 2013). This advantage allows preying upon small fish below

10 cm, which were found to represent an important food source (Wisniewska et al., 2016).

Additionally, the development of a high frequency biosonar represents a selective advantage,

since echolocation clicks are outside the hearing range of killer whales (Orcinus orca)

(Szymanski et al., 1999), which prey upon harbour porpoises (Cosentino, 2015).

II. Hearing adaptations

Mammalian hearing is accomplished by an outer ear, which receives acoustic signals, a middle

ear, which amplifies and filters signals and the inner ear and thus functions as a mechano-

chemical transducer (Ketten, 1997). This land mammal blueprint is generally followed by

cetacean ears; however, adaptations to aquatic life have evolved (Nummela et al., 2004).

Underwater hearing requires further adaptations of the ears, compared to in-air hearing, as these

do not function as a converter from airborne- to fluid-borne sound in the inner ear. In contrast,

an acoustic isolation of the inner ear from the environment is needed, because the density of

water is similar to the tissue, while in air the tissue is much denser (Fenton et al., 2014).

Therefore, evolutionary adaptations are required to compensate for the mismatch in impedance

(Cranford et al., 2010; Fenton et al., 2014). During evolutionary development the external

auditory meatus was eliminated in Odontocetes (Nummela et al., 2004). External auditory

canals lack an observable connection with the temporal bones or tympanic membrane and are

furthermore plugged with dense cerumen and cellular debris (Ketten, 1997). An acoustic

isolation of the inner ears is enhanced by dense tympanic and periotic bones, which are isolated

in sinuses (cited in Fenton et al., 2014). Acoustic signals arrive at the tympanoperiotic complex

through an ‘acoustic window’, a hollow section surrounding the lower jaw, which opens

caudally (Nummela et al., 2007). This section is filled with fat bodies, encapsulated in

connective tissue, with the function to focus incoming sound (reviewed in Koopman, 2018;

Varanasi et al., 1975). The acoustic fat bodies in the lower jaw have a similar density than

seawater, which enables a fast sound transmission. The acoustic fat channels are inserted into

the tympanic plate, which is a particular site of the tympanoperiotric complex, characterized by

Introduction

4

very thin portions of the ventrolateral wall of the tympanic bulla (Nummela et al., 1999). The

process of the malleus receives vibrations of the tympanic bone through a synostosis connection

to the tympanic plate (Cranford et al., 2010; Nummela et al., 1999). Vibrations are conducted

via the osseous chain to the cochlea, where these are transformed into electrical signals

(Cranford et al., 2010; Nummela et al., 1999). The emission of intense outgoing clicks during

echolocation necessitates an isolation from the sending and receiving pathway. This is achieved

by the lower jaw pathway, which allows for an improvement of echolocation performance with

excellent sensitivity and directionality in high frequency hearing of toothed whales (Aroyan,

2001; Au and Moore, 1984; Hemilä et al., 2010; Ketten, 1997; Rauschmann et al., 2006).

Over a period of 60 million years, marine mammals evolved anatomical and physiological

modifications, which enabled the transition from terrestrial to aquatic specialists (cited in

Williams and Worthy, 2002). One challenge which has to be overcome is the locomotion,

impeded by an 800 times higher density and 60 times higher viscousity of water in comparison

to air (Dejours, 1987). A 24 times higher thermal conductivity of water is also challenging for

endothermic mammals, trying to prevent heat loss to the comparatively cold environment of

the ocean (Dejours, 1987; Williams and Worthy, 2002). A concurrent heat loss is mitigated by

a blubber layer, which undergoes cyclical fluctuations to compensate extra costs for

thermoregulation during winter (Rojano-Doñate et al., 2018).

The harbour porpoise (Phocoena phocoena) is the smallest representative amongst the marine

mammals. It shows a high surface-to-volume ratio suggesting to find them in rather warm water

environments, but they exclusively inhabit coastal waters of the northern hemisphere (Gilles et

al., 2016; Hammond et al., 2017). Survival in this cold environment is enabled by elevated field

metabolic rates, which are up to two times higher than for terrestrial mammals of comparable

size (Rojano-Doñate et al., 2018). These findings are in line with determined feeding rates of

wild porpoises, which can reach up to 550 small fish per hour (Wisniewska et al., 2016). There

is scientific evidence, that the high energy demands can only be maintained by almost

continuously foraging, which would demonstrate a low resilience to any disturbance

(Wisniewska et al., 2018a, 2016).

III. Communication

The key to success, when living in an apparently infinite environment, is communication.

Information is exchanged between a sender and a receiver to fulfil multiple kinds of tasks

Introduction

5

(Bradbury and Vehrencamp, 2011; Cholewiak et al., 2018). These messages can contain

information on the position and identity of group members (Lammers and Au, 2003) or food

patches (King and Janik, 2015; Parks et al., 2014), are under suspect to serve essential functions

during mating behaviour (Herman, 2017) or may even elicit anti-predator responses, e.g. when

eavesdropping on killer whale sounds (Curé et al., 2013). The marine environment physically

differs from the terrestrial one. Visibility is strongly limited underwater by the higher absorption

of light by suspended and floating particles (Dejours, 1987). Therefore, even in the photic zone,

underwater vision is barely the key to great hunting success. Although suspended particles limit

vision, these contribute to the four-times higher sound velocity in the water, making acoustic

communication efficient and often the only viable communication channel. With a speed of

sound of approximately 1500 m/s (Dejours, 1987) acoustic communication is the ultimate tool

for communication. Soniferous representatives were found in almost all classes of the animal

kingdom that inhabit the marine environment. Acoustic communication plays a major role for

both, invertebrates (Montgomery et al., 2017; Vermeij et al., 2010) and vertebrates (Clausen et

al., 2010; Ladich, 2019; Ladich and Winkler, 2017; Sørensen et al., 2018). Baseline hearing

abilities could be shown for a variety of fish species from multiple families (reviewed in Ladich

and Fay, 2013). Vocalizations are emitted during courtship or spawning by fishes (Amorim et

al., 2015) or may even mark a territory (Amorim, 2006; Ladich and Myrberg, 2006).

Soundscape ecology, derived from acoustic monitoring, allows for the assessment of

biodiversity, monitoring the health of habitats and the localisation of spawning grounds

(reviewed in Lindseth and Lobel, 2018). While acoustic signalling supports on the one hand the

reproductive success of Atlantic cod (Rowe and Hutchings, 2008), these signals could

concurrently reveal the presence of the fish to predators. Acoustic cues might be used by passive

listening predators, which might be the reason for a large proportion of soniferous fish species

in the diet of dolphins (Burros and Myrberg, 1987). This passive listening theory was validated

through playbacks of prey fish calls, which elicited attraction in bottlenose dolphins (Tursiops

truncatus, Gannon et al., 2005).

Active acoustic communication is the key for marine mammals, which all produce sound in

various contexts (reviewed in Erbe et al., 2016). The emission of species-specific calls has been

associated with mating behaviour in multiple baleen whale species (Croll et al., 2002; Herman,

2017) and seal (Frouin-Mouy et al., 2016; Nikolich et al., 2018; Rogers, 2017) species. The

Introduction

6

mating calls of male bearded seals are just one vivid example for the complexity and highly

developed vocalisations in marine mammals (Frouin-Mouy et al., 2016). The trill calls typically

have a duration of 30 s and consist of numerous repetitions of short sweeps with decreasing

frequency over time (Frouin-Mouy et al., 2016). These stereotypic calls were associated with

the mating period, potentially advertising the breeding condition of males (Frouin-Mouy et al.,

2016; Rogers, 2017). Moreover, single calls can contain sufficient information for recognition

between mother and calves, which is for instance essential for survival in colonial pinnipeds

(Charrier et al., 2010; Insley et al., 2003). Dolphins even have evolved individually distinctive

signature whistles, which share information about the identity of the caller and maintain group

integrity. When isolated from conspecifics, these calls can account for 90% of all vocalisations

(reviewed in Janik and Sayigh, 2013). These whistles account for 38 – 70% in wild animals

(reviewed in Janik and Sayigh, 2013), which develop individual calls during the first year of

life and retain it throughout life (Sayigh et al., 1990). Some species display variations in their

vocal repertoire, which are described as dialects, since these differences occur between groups,

which could potentially interbreed (Conner, 1982). The evolution of different dialects enables

to differentiate between members of different populations living within the same geographic

region (Ford, 1989; Weilgart and Whitehead, 1997).

IV. Determination of hearing thresholds

Auditory thresholds can be measured using two different techniques, which substantially differ

in application possibilities and results. The hearing of marine mammals can either be tested

using psychophysical procedures, which requires extensive training of animals (Kastelein et al.,

2002, 2019b) or by neurophysiological methods with trained (Nachtigall et al., 2016) or

temporarily restrained individuals (Ruser et al., 2014, 2016a). The psychophysical method to

measure audiograms is regarded as the gold standard (Houser et al., 2017), but requires previous

extensive training of the animals by experienced animal trainers. The animals are conditioned

to display, if they heard a hearing test stimulus by the use of positive reinforcement (e.g.

Kastelein et al., 2019; Nachtigall et al., 2017). Hearing thresholds are accordingly determined

testing different sound pressure levels (SPLs). The neurophysiological technique is an indirect

method, because brainstem responses are measured, which are auditory evoked. Auditory

evoked potentials (AEP) are small electrical charges generated by the brain in response to an

acoustic stimulus, which can be measured on the body surface of a harbour porpoise by using

Introduction

7

electrodes imbedded in suction cups. This method allows for a fast audiometric measurement

without the necessity of preliminary conditioning (Supin et al., 2001). The application of the

AEP method to collect audiograms has gained in popularity over the last decade (Houser et al.,

2017). Although the general pattern does not substantially differ between psychophysically and

neurophysiologically derived audiograms, the absolute hearing threshold can differ by up to

31 dB (Mulsow and Reichmuth, 2010). Therefore, comparisons of hearing thresholds gathered

with different techniques have to be made with great caution. However, the AEP method does

not require previous training and is therefore well suited for the application in the field (Ruser

et al., 2016a) or for wild animals (Ruser et al., 2014).

V. Effects of anthropogenic underwater noise pollution

Since toothed whales rely critically on echolocation to find prey and perceive their environment,

they are especially vulnerable to interferences by noise. A significant source of disturbance for

marine life is the substantially increasing anthropogenic underwater noise pollution, which is

now recognized as a global problem (Erbe et al., 2019; Shannon et al., 2016; Williams et al.,

2015). Effects of increased anthropogenic noise pollution are particularly assessed in humans,

with strong evidence for psychological and physiological consequences like cognitive

impairment (Szalma and Hancock, 2011), sleep deprivation (Fyhri and Aasvang, 2010) or a risk

of cardiovascular diseases (Babisch et al., 2005; Hansell et al., 2013). As reviewed by Shannon

et al. (2016), protective legislation for humans was already implemented in the seventies in the

USA (Noise Control Act of 1972, Quiet Communities Act of 1978) and in 2002 in the European

Union (Environmental Noise Directive 2002/49/EC). The assessment of potential effects of

noise on aquatic life is challenging due to limited accessibility to animals. Further complications

in the quantification arise from the fact that the sensitivity to noise varies across taxa (Brumm

and Slabbekoorn, 2005; Shannon et al., 2016; Southall et al., 2019). Furthermore, even intra-

specific sensitivities occur depending on life history, context or sex (reviewed e.g. Ellison et

al., 2012 or Francis and Barber, 2013).

Biological consequences of noise exposure can be reflected on multiple scales. An exemplary

categorization to summarize biological responses towards effects of noise has been proposed

by Shannon et al. (2016) comprising nine different classes. Noise pollution can accordingly

affect the physiology of animals 1) by means of stress, hearing impairment, immunosuppression

or gene expression. The fitness of animals 2) can be directly affected, represented in survival

Introduction

8

rates, fecundity or birth rate or indirectly by effects on 3) mating behaviour in terms of

attraction, mating success, territorial behaviour or pair bonding. These results can be an effect

from masking, which means that biologically relevant signals cannot be recognized, since these

overlap with noise. Potential effects of noise can concern 4) the foraging behaviour in terms of

foraging rate and success. The exposure to noise can influence animals 5) movement

represented by the spatial distribution or could induce flight responses or alterations in diving

behaviour. The vigilance of animals 6) can be affected, which could secondary affect other

behavioural states and could therefore lead to missed foraging opportunities. Effects of noise

on the vocal behaviour 7) can be expressed by changes in the call rate, intensity, frequency,

signal duration, call type and timing of signals. Widespread effects can concern the population

metrics 8) such as abundance, occupancy, settlement or density but also the community level

9), regarding species composition and predator prey interactions (all classes cited from Shannon

et al., 2016).

Ship traffic has become the most pervasive and ubiquitous source of underwater noise pollution

in the recent decades caused by the globalisation of transportation networks, population growth

and expansion of resource extraction (Erbe et al., 2016; Shannon et al., 2016; Williams et al.,

2015). Between 1992 and 2012, the global ship density quadrupled, leading to a steady rise in

ambient noise levels between 10 and 100 Hz a high as 3 dB per decade (Andrew et al., 2002,

2011; Chapman and Price, 2011; Kleinertz et al., 2014; Miksis-Olds et al., 2013; Miksis-Olds

and Nichols, 2016). Vessel noise is considered to be a continuous noise source and has the

potential to elicit strong behavioural responses in harbour porpoises (Akkaya Bas et al., 2017;

Dyndo et al., 2015), which are assumed to indicate disturbance. Wild harbour porpoises in the

Inner Danish waters were exposed to vessel noise in 17 to 89% of the time these animals were

tagged with sound and movement recording tags (Wisniewska et al., 2018b). During the

exposure to vessel noise exceeding 96 dB re 1 µPa (in the 16 kHz third-octave band)

behavioural changes of the tagged harbour porpoises occurred (Wisniewska et al., 2018b). The

animals increased the fluke strike rate, resulting in an increased swim speed and stayed close

to the bottom (Wisniewska et al., 2018b). Additionally, a cessation of echolocation and a

significant decrease of foraging behaviour was determined for these animals (Wisniewska et

al., 2018b), which were found to feed almost continuously to maintain high energy demands

(Wisniewska et al., 2018a, 2016).

Introduction

9

Anthropogenic underwater noise also occurs in brief bursts of sound pressure, which are defined

as impulsive noise (ISO, 2016). Typical sources of anthropogenic impulsive noise are (1)

underwater explosions (e.g. von Benda-Beckmann et al., 2015), which occur when unexploded

ordnance of World War II are cleared, (2) seismic surveys with large arrays containing multiple

air guns in order to locate deposits of fossil fuels in the seafloor (e.g. Sarnocińska et al., 2020)

and (3) pile driving noise, which is emitted when fundaments are driven into the seabed (Brandt

et al., 2018; Graham et al., 2019; Leunissen and Dawson, 2018). These impulsive noise sources

are often characterized by high source levels, leading to higher local effects than vessel noise

(Hildebrand, 2009).

The exposure to impulsive noise with high received levels can be lethal or induce severe injuries

when haemorrhages occur in air filled cavities, around the brain or embolisms arise from

nitrogen bubble transformations in the blood stream (Cox et al., 2006; Fernández et al., 2005;

Siebert et al., 2013). Less severe injuries can affect the hearing of marine mammals (reviewed

in Finneran, 2015), which are not directly lethal, but can have dramatic secondary effects.

Affected hearing can influence the survival rate of single individuals (Mann et al., 2010; Morell

et al., 2017a). Interferences may even result in decreased individual fitness and could lead to

long-term population consequences (King et al., 2015). The exposure to impulsive noise has

the potential to induce physiological changes, such as hearing loss (Lucke et al., 2009). A shift

in hearing ability after the reception of a fatiguing noise may recover, in which case it is defined

as a temporary threshold shift (TTS) or may not resolve, leading to a permanent threshold shift

(PTS) (Finneran, 2015). Noise induced hearing loss can be a result from a very high-level single

impulsive sound event (Lucke et al., 2009), which is typically of short duration or from the

exposure over substantially longer periods to lower-level sounds (Kastelein et al., 2015d, 2016).

Such a TTS affects the hearing threshold for a certain frequency range rather than the complete

hearing curve (Lucke et al., 2009; Popov et al., 2013). The TTS is expressed at the main

frequency of the fatiguing stimulus, but is highest half an octave above the peak frequency for

large hearing shifts (Popov et al., 2013). Moreover, hearing impairment can severely affect

essential life functions (Morell et al., 2017a, 2017b) such as finding and catching prey

(DeRuiter et al., 2009; Verfuß et al., 2009), navigation (Verfuß et al., 2005), communication

with intra-specifics (Clausen et al., 2010; Sørensen et al., 2018) and avoid (Curé et al., 2013)

or find (Gannon et al., 2005) inter-specifics.

Introduction

10

VI. Protective regulations for harbour porpoises

Three marine mammal species are considered to reproduce regularly in German waters. The

harbour seal (Phoca vitulina), the grey seal (Halichoerus grypus) (CWSS, 2017) and the

harbour porpoise (Phocoena phocoena) (Gilles et al., 2016). Although seals display highly

developed hearing abilities in air (Ruser et al., 2014) and underwater (Kastelein et al., 2009a,

2009b), which indicates a necessity for sound perception, this thesis is focused exclusively on

the only Odontocete representative. Among the toothed whales, which are generally vulnerable

to noise disturbance, harbour porpoises are considered to be very sensitive to effects of noise

and are therefore regarded as an indicator species in noise impact evaluations (Southall et al.,

2019; Tougaard et al., 2015). Harbour porpoise distribution extends to coastal waters of the

northern hemisphere, including the Baltic Sea, Black Sea, Northern Atlantic and the North

Pacific (cited in Bjørge and Tolley, 2018). The North- and Baltic Seas are inhabited by three

different harbour porpoise populations, which are distinguished as the North Sea population,

the Inner Danish Waters population and the Baltic proper population (Galatius et al., 2012;

Huggenberger et al., 2002; Wiemann et al., 2010). In a large scale survey in 2016, harbour

porpoise abundance in the North Sea was estimated at 345,373 individuals (CI: 246,526-

495,752), whereas the Kattegat and Belt Seas account for an abundance of 42,324 individuals

(CI: 23,368-76,658, Hammond et al., 2017). Since the population of the Baltic proper was

estimated at 497 animals (CI: 80-1,091, Amundin 2016), this population is considered as

“critically endangered” by the IUCN (Carlén et al., 2018). Harbour porpoises display a sexual

dimorphism with smaller males with a length of about 145 cm and a weight of 50 kg, whereas

females reach average sizes of 160 cm and a weight of 60 kg (reviewed in Bjørge and Tolley,

2018). Nevertheless, maximum female sizes of 200 cm with a weight of 70 kg have been

reported occasionally (cited in Bjørge and Tolley, 2009). Sexual maturity was estimated in

female harbour porpoises of the German North- and Baltic Seas at an age of 4.95 years (±0.6)

(Kesselring et al., 2017). Harbour porpoises are predominantly piscivorous and are considered

as opportunistic predators (Andreasen et al., 2017), which forage nearly continuously

(Wisniewska et al., 2016) to meet high energy demands (Rojano-Doñate et al., 2018). The most

abundant prey species in harbour porpoise diet depends on prey availability within the region

or during season (Andreasen et al., 2017; Benke et al., 1998; Wisniewska et al., 2016).

Introduction

11

In European waters, harbour porpoises are protected amongst others within the framework of

the Habitats Directive (listed in annexes II and IV European Union, 1992) and Council

Regulation 812/2004 (European Union, 2004). This protective regulation implies that special

areas should be established for their conservation with deliberate actions of killing, disturbing,

injuring and habitat deterioration being prohibited throughout its area of distribution (Council

Directive 92 / 43 / EEC, Article 12.1). Furthermore, harbour porpoises are protected by the

agreement of ten European Union member states on the conservation of small cetaceans in the

North and Baltic Seas (ASCOBANS, 2002, 2012), as well as by the Baltic Marine Environment

Protection Commission (Helsinki Commission, HELCOM) in the Baltic Sea and the

Convention for The Protection of the Marine Environment of the North-East Atlantic (the

OSPAR Convention) in the North Sea.

Although the prevention of injuries in marine mammals has been considered globally (e.g. by

the Habitats Directive in Europe or by the U.S. Marine Mammal Protection Act in the United

States), “injury” is defined differently in national policies. According to the Federal Ministry

for the Environment, Nature Conservation, and Nuclear Safety (BMU, 2014) in Germany, a

temporary loss of hearing after exposure to pile driving noise is considered as injury, whereas

most other European countries or the United States only regard a permanent hearing shift (PTS)

as injury. There is no common EU regulation to protect harbour porpoises from hearing

impairment during the construction of offshore wind farms in the EU (Stöber and Thomsen,

2019). However, noise mitigation measures are already obliged in Belgium, Denmark,

Germany and the Netherlands. Belgium and the Netherlands additionally restrict pile driving

activities to designated periods. Germany has enforced the strictest regulations in the EU to

date, by limiting the maximum sound exposure level (SEL) to 160 dB re 1 μPa²s and a

maximum sound pressure level (SPL) of 190 dB re 1 μPa for a single strike at a distance of

750 m (BMU, 2014). Furthermore, wind farm operators are obliged to deter harbour porpoises

prior to pile driving activities and to use a soft start procedure with limited force and longer

pulse intervals in the beginning (BMU, 2014). Despite the regulations of pile driving noise,

there is no further regulation of noise emission.

Introduction

12

VII. Motivation

The aim of this doctoral thesis is to tackle the gap in current protective regulations and identify

present anthropogenic noise sources with the potential to induce a TTS in harbour porpoises.

Since the sources of anthropogenic noise are numerous, this study focuses on a selection of

three, covered in individual chapters:

Chapter 1 is dedicated to the current protective regulations of noise mitigation during the

construction of offshore wind farms in German waters (BMU, 2014). Part of this is the analysis

of underwater noise recordings, which were gathered during the construction of the offshore

wind farm “Amrumbank West”. This wind farm is of particular interest, since it was adjacently

built to the special protection area “Sylt Outer Reef” within the Exclusive Economic Zone

(EEZ) of the German North Sea, which shows high harbour porpoise densities (Gilles et al.,

2011) and serves as an important calving ground (Gilles et al., 2009). The 80 wind turbines of

this wind farm were constructed in compliance with the current noise mitigation concept of the

Federal Ministry for the Environment; Nature Conservation and Nuclear Safety (BMU, 2014).

The output of this study is an evaluation tool, which helps to evaluate the TTS potential for

fleeing harbour porpoises from the reception of multiple pile driving strikes, which is not

considered in the German noise mitigation regulations yet.

Chapter 2 represents the results of a study with a harbour porpoise in human care. Hearing tests

were conducted with an animal held at the Fjord & Bælt Centre in Kerteminde (DK) to test,

whether a seal scarer signal has the potential to induce a TTS in harbour porpoise hearing. These

acoustic deterrent devices (ADDs) are applied in two different situations. ADDs are used to

deter harbour porpoises prior to pile driving activities with the aim to clear the area close to the

construction site (BMU, 2014), where a TTS can be induced by pile driving noise (Lucke et al.,

2009). In this situation ADDs serve as a mitigation method, which wind farm operators are

obliged to follow. ADDs are also applied around marine aquacultures to deter seals in order to

counteract depredation (Dawson et al., 2013). This kind of application represents a significant

chronic noise source over a large spatial range along the Scottish West coast (Findlay et al.,

2018), which overlaps with harbour porpoise occurrence (Embling et al., 2010; Hammond et

al., 2013), as a non-target species. The aim of this study was to determine a minimum sound

energy level, at which a temporary threshold shift can be induced (SEL-TTSonset) by a single

ADD signal. The hearing thresholds were derived from measurements of auditory evoked

Introduction

13

potentials (AEP) prior to and after the exposure to artificial seal scarer signals. The SEL-

TTSonset as an output of this study can serve as an orientation to down regulate ADD source

levels, to enable pursuing application without the risk of a TTS.

Chapter 3 is dedicated to a situation of unintended effects of noise exposure in an area, which

is regularly visited by harbour porpoises. Harbour porpoises seasonally occur in the port of

Hamburg, an area that is highly exposed to ship traffic with vessels of all kinds and sizes.

Despite the high levels of vessel noise they show a seasonal occurrence, which might be driven

by anadromous prey fish, migrating upstream the Elbe River in spring. Within the area of

harbour porpoise occurrence in the port of Hamburg, the flow velocity is measured by acoustic

signals, which are in the frequency range of harbour porpoise hearing. This measuring device

was under suspect to be the cause of death for several harbour porpoises in the Elbe River in

2016. This study aims for a TTS risk assessment for this acoustic flowmeter, by the analysis of

underwater recordings in the port of Hamburg, sound exposure experiments with a harbour

porpoise in human care at the Fjord & Bælt Centre in Kerteminde (DK) and a simulation

approach to estimate the TTS potential for harbour porpoises travelling along the acoustic

flowmeter. The output of this study is an evaluation of the flowmeter to induce a TTS in harbour

porpoises and to provide management suggestions for potentially needed adjustments of the

acoustic flowmeter.

The overarching goal of this thesis is to assess the effect of noise disturbance from different

sources as an antagonist, interfering with acoustic perception of the environment. The aim is to

shed light on gaps in noise regulation and raise attention for the naive application of acoustic

devices, since harbour porpoises are particularly vulnerable to interferences by noise due to

their dependence from acoustically sensing their environment.

Effects of multiple exposure to pile driving noise on harbor porpoise hearing during

simulated flights – an evaluation tool.

14

Published:

Reproduced from,

Schaffeld, T., Schnitzler, J.G., Ruser, A., Woelfing, B., Baltzer, J., Siebert, U. (2020). Effects of multiple exposure to pile driving noise on harbor porpoise hearing during

simulated flights – an evaluation tool. Journal of the Acoustical Society of America,

147 (2), 685-697, https://doi.org/10.1121/10.0000595

with the permission of the Acoustical Society of America.

Chapter 1: Effects of multiple exposure to pile driving noise on harbor porpoise

hearing during simulated flights – an evaluation tool

15

Chapter 1: Effects of multiple exposure to pile driving noise on harbor

porpoise hearing during simulated flights – an evaluation tool

T. Schaffeld, J.G. Schnitzler, A. Ruser, B. Woelfing, J. Baltzer, U. Siebert.

Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine

Hannover, Foundation, Werftstraße 6, 25761 Büsum, Germany

This paper is part of a special issue on The Effects of Noise on Aquatic Life.

Abstract

Exploitation of renewable energy from offshore wind farms is substantially increasing

worldwide. The majority of wind turbines are bottom mounted, causing high levels of impulsive

noise during construction. To prevent temporary threshold shifts (TTS) in harbor porpoise

hearing, single strike sound exposure levels (SELSS) are restricted in Germany by law to a

maximum of 160 dB re 1µPa²s at a distance of 750 m from the sound source. Underwater

recordings of pile driving strikes, recorded during the construction of an offshore wind farm in

the German North Sea, were analyzed. Using a simulation approach, it was tested whether a

TTS can still be induced under current protective regulations by multiple exposures. The

evaluation tool presented here can be easily adjusted for different sound propagation, acoustic

signals or species and enables to calculate a minimum deterrence distance. Based on this

simulation approach, only the combination of SELSS regulation, previous deterrence and soft

start allow harbor porpoises to avoid a TTS from multiple exposures. However, deterrence

efficiency has to be monitored.



16

Author contributions

J.B., T.S. and A.R. were involved in the underwater noise recordings around the Offshore Wind

Farm. T.S. and A.R. conceived the original theory for this simulation approach, which was

further developed with support from J.S. and B.W.. The sound propagation modelling was

performed by T.S. and J.S. T.S. performed the computations of the simulations and figures.

Mathematical equations were derived by B.W. T.S. wrote the manuscript. T.S. was supervised

by A.R., J.S. and U.S. All authors provided critical feedback and helped shape the research,

analysis and manuscript.



17

I. Introduction

The marine environment provides an almost infinite source of offshore renewables, which may

be exploited with limited negative environmental impacts if guidelines are followed and the

planning and scaling of projects are suitable (Pelc and Fujita, 2002). Increasing efforts were

made worldwide to exploit offshore renewables. In Germany, plans to refrain from extracting

energy from fossil fuels or to close down nuclear power plants have been made over the last

years and became even more ambitious after the disaster in 2011 at the nuclear power plant in

Fukushima (Japan). Eighty percent of energy demands in Germany should be covered by

renewable forms of energy by 2050. Since 2009 the German Federal Government’s goal has

been to reach 25 Gigawatt by 2030 from offshore wind capacity by undertaking intensive

building of offshore wind farms (OWF) in German waters (BMWI, 2012). In total, 92 offshore

wind farms have been constructed to date in eleven European countries including sites with

partial grid connection, accounting for 4149 connected wind turbines (Remy and Mbistrova,

2018). This increased human encroachment overlaps with protected areas like the Sylt Outer

Reef and could have negative effects on health, distribution and behavior of key ecological

species inhabiting German offshore areas.

The inconspicuous and only resident cetacean in the German North Sea is the harbor porpoise

(Phocoena phocoena). It inhabits coastal waters and is therefore subject to anthropogenic

pressures, e.g. accidental bycatch (ASCOBANS, 2002), continuous shipping noise (Akkaya

Bas et al., 2017; Dyndo et al., 2015; Wisniewska et al., 2018b) and impulsive noise from pile

driving (Brandt et al., 2018; Tougaard et al., 2009), seismic surveys (Pirotta et al., 2014) or

underwater explosions (von Benda-Beckmann et al., 2015). In European waters, harbor

porpoises are protected among others within the framework of the Habitats Directive (listed in

annexes II and IV (European Union, 1992)) and Council Regulation 812/2004 (European

Union, 2004), implying that special areas should be established for their conservation with

deliberate actions of killing, disturbing, injuring and habitat deterioration being prohibited

throughout its range (Council Directive 92 / 43 / EEC, Article 12.1).

Although the prevention of injury in marine mammals has been considered globally (e.g. by the

Habitats Directive in Europe or by the U.S. Marine Mammal Protection Act in the United

States), injury is defined differently in national policies. According to the Federal Ministry for

the Environment, Nature Conservation, and Nuclear Safety (BMU (2014)) in Germany, a



18

temporary loss of hearing after exposure to pile driving noise (temporary threshold shifts, TTS)

is considered as an injury, whereas most other European countries or the United States regard

a permanent hearing shift (PTS) as an injury. Lucke et al. (2009) derived data on TTS induced

by single impulsive airgun stimuli, and defined an onset at a sound exposure level (SEL) of

164 dB re 1 µPa²s at a hearing frequency of 4 kHz, showing that harbor porpoises are more

sensitive to impulsive noise than other high frequency cetaceans (reviewed in Southall et al.,

2019). Consequently, the BMU published a regulation, which restricts the maximum SEL to

160 dB re 1 µPa²s for single impulsive noise at a distance of 750 m from the source (BMU,

2014) in reference to the findings of Lucke et al. (2009). To keep noise levels below this

threshold, wind farm operators are obliged to use most innovative noise mitigation systems

(NMS) like bubble curtains (Dähne et al., 2017; Lucke et al., 2011; Würsig et al., 2000) and

hydro sound dampers (HSD, Elmer et al. 2012). Additionally, acoustic deterrent devices (pinger

and seal scarer) are deployed before pile driving, to deter animals from the area, where noise

levels can exceed the threshold for an SEL of a single strike of 160 dB re 1 µPa²s.

Recent studies showed that besides the danger from a single pulse with high energy, the

reception of multiple pile driving strikes with single strike sound exposure levels (SELSS) well

below the legal threshold can also induce a TTS because of the total received energy. Indeed,

playbacks of pile driving sounds at an SELSS of 146 dB re 1 µPa²s induced a TTS in harbor

porpoises. A significant TTS at 4 and 8 kHz occurred after the playback of 2760 strikes within

60 minutes (Kastelein et al., 2015a). A TTSonset at 8 kHz hearing frequency was determined at

a cumulative SEL (SELcum) of 175 dB re 1 µPa²s, corresponding to 1385 pile driving strikes of

145 dB re 1 µPa²s (SELSS) in 30 minutes (Kastelein et al., 2016). Although regulations to

protect harbor porpoises from TTS by single impulsive sounds have already been established,

it was shown that the multiple reception of pile driving strikes can still induce a TTS.

In our present study, potential auditory hazard zones were estimated, within which hearing

impairment is theoretically possible for harbor porpoises. Several behavioral scenarios were

considered, which simulate effects for harbor porpoises that stay within the area of noise

exposure and those that show a flight response at different literature-based swim speeds. The

accumulation of sound energy from multiple pile driving strikes for harbor porpoises is

determined by using real underwater recordings from recent pile driving activities in the

German North Sea and its sound propagation. We estimated the potential to induce a TTS based



19

on the distance to the pile driving site, and identified the minimum distance a harbor porpoise

must be away from the pile driving site at the moment of the first strike to avoid auditory

impairment.

The aim of this study is to provide a tool to evaluate effects of multiple pile driving events on

harbor porpoise hearing. Equations presented here are adjustable for areas with differing sound

propagation or further species with different TTS onsets, and allow the necessary minimum

deterrent distances to be estimated. The outcomes of this study will highlight the efficiency of

current protective measures in force in Germany to prevent temporary hearing shifts in harbor

porpoises from pile driving noise. Currently, these measures restrict the maximum single strike

exposure levels to 160 dB re 1 µPa²s at a distance of 750 m and the use of acoustic deterrent

and harassment devices which are deployed before pile driving.



20

II. Material & Methods

A. Study site and pile driving recordings

Underwater recordings during the construction of 50 monopiles were conducted between

August 27th 2014 and March 18th 2015 in order to determine underwater noise. Therefore,

Autonomous Multichannel Acoustic Recorders (AMAR, JASCO Applied Sciences, , Canada)

were bottom mounted at a depth of 20 m at seven measuring positions in the surrounding area

of the German offshore Amrumbank West wind farm at distances between 2.4 and 36.8 km to

pile driving sites (see FIG. 1 for further details on measuring positions and piles). Distances

between measuring positions and pile driving sites could be determined by logging the position

of measuring stations and reported pile positions by the wind farm operator. Background

underwater noise was continuously recorded in 30 min files sampling at 32 ksamples s-1 and a

16-bit resolution. All AMAR recorders were equipped with omnidirectional GTI-M8E

hydrophones (GeoSpectrum Technologies Inc., Dartmouth, Canada) with nominal sensitivities

of -160 and -200 dB re 1VµPa-1. In order to compensate for different received levels of pile

driving strikes, less sensitive hydrophones were deployed at closer distances. The recording

system was protected from bottom trawling by a trawl shield, meaning a glass fiber reinforced

plastic housing (270×1250×1000 mm, H×W×D, 8 mm material thickness) built by DW-

ShipConsult GmbH, Schwentinental Germany (see picture of trawl shield in Gerdes and Görler

(2016), Fig. 3 (right picture)). The trawl shield contained cropped circles on every side for a

better sound transmission. The hydrophone was fixed inside the trawl shield below a cropped

circle in a vertical position, pointing in the direction of the sea surface. External battery supplies

were also employed inside the trawl shield to enable continuous recording over an

approximately three-month period. The applied recording system fulfilled the requirements of

ISO 18406 (2017) and the German guidelines (Müller and Zerbs, 2011) in terms of sampling

frequency, data format, self-noise of the mooring system and electronic components,

hydrophone sensitivity (<2dB over the frequency range from 0.02 to 16 kHz) and interval of

calibration (two years).

The investigated monopiles were deployed by two different wind farm installation vessels (MPI

Discovery (Flag: the Netherlands) & HLV Svanen (Flag: the Bahamas)). Further vessels

applied big bubble curtains (BBC) and hydro sound dampers (HSD) for noise mitigation.

Further information about the application of these NMS during the construction is not publicly



21

accessible. Therefore, we cannot distinguish which NMS or combination of different NMS was

utilized.

FIG. 1: Research area in the German North Sea with marked positions of underwater recorders

(triangle) and positions where pile driving activities were conducted (points). Offshore

wind farms (OWF) which are active to date are marked as solid areas, while OWF, which

are planned or under construction are shown as dashed areas. Dashed lines represent

FFH protected areas (European Union, 1992). A zoom in on the research area (square)

is shown in the top-right figure.

B. Sound propagation modelling and frequency analysis

Single strike sound exposure levels (SELSS) for the full frequency spectrum were calculated for

each measuring position and constructed pile foundation in accordance with German

measurement guidelines (Müller and Zerbs, 2011). All pile driving strikes, which were detected

in the underwater noise recordings over the entire construction period, were analyzed. The

median SELSS of all pile driving strikes per hour (SEL50 h-1) was determined for each station

and pile, describing the accumulated sound energy of these impulsive noise events related to

1 s and the reference pressure of 1 µPa (ISO 18406, 2017).



22

The sound propagation, based on the determined median SELSS per hour and distances to the

pile driving site, was estimated by a non-linear regression. The intercept and the logarithmic

regression factor were estimated by a non-linear least squares approach, using the nls function

in R (R Core Team, 2019). Furthermore we estimated the decay factor A in dB per meter within

the nls approach. A weighting was applied to the model regarding the number of pile driving

strikes within the analyzed hour. The received level (RL) was estimated as

𝑅𝐿(𝑅𝐾) = 𝐼𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡 − 𝑠𝑙𝑜𝑝𝑒 × 𝑙𝑜𝑔10(𝑅𝑘) − 𝐴(𝑅𝐾) (1),

where Rk is the distance to the pile driving site, the intercept is the intercept of the regression,

the slope is the slope of the regression, which is expected in the range of 10-20 and the decay

factor A, which is a result from multiple reflections from the surface and seabed (Ainslie et al.,

2014; Lippert et al., 2018; Martin and Barclay, 2019; Zampolli et al., 2013). The estimated

propagation parameters slope and A depend on the surface and bottom roughness, the sediment

type and the speed profile within the water column. This sound propagation model was

empirical based, but has to be considered as a broad estimate, because it does not consider any

variations in bottom composition or bathymetry. Although sound propagation is much more

complex and local variability may occur, this simple model enables a conceptual understanding

of the propagation of pile driving noise (Ainslie et al., 2014; Lippert et al., 2018; Martin and

Barclay, 2019).

For comparative reasons, we also modeled a theoretical transmission loss (TL) over distance

(Rk), which would be expected if guidelines are followed. The radiation characteristic of pile

driving noise is considered to be more similar to a line than a point source, since the pile as a

resonating body covers the entire water column in most of the cases. The proposed damped

cylindrical spreading decay formula (Zampolli et al., 2013) considers this sound propagation

and has been shown to be applicable for pile driving noise propagation within the North Sea up

to a distance of approximately 15 km (Lippert et al., 2018). Based on the current German

regulation, we assumed an SELSS of 160 dB re 1µPa²s at a distance of 750 m. The theoretical

received level (RL) at the distance Rk was obtained from equation (1), under the assumption

that pile driving noise follows a damped cylindrical spreading, with Rk as the reference range

of 750 m, where the SELSS is equal to 160 dB re 1 µPa²s. The decay factor was estimated by

an empirical fit within a non-linear model, based on our empirical data of SEL50 h-1 over



23

distance for data up to 15 km and the number of pile driving strikes per hour as a

weighting factor. Ambient noise was determined for a 30 s fraction of underwater sound

recordings prior to pile driving activities, when no pile driving strikes occurred. Third octave

spectra (2-base) were calculated for each 10 Hz high pass filtered 1 s window within the time

window, for each pile at each measuring position for center frequencies ranging from 62.5 Hz

to 12.7 kHz. In total, background recordings prior to six pile driving events at two measuring

positions were analyzed, forming a database of eleven 30 s windows.

C. Model assumptions

The calculation of the potential hazard zone for auditory damages was based on several

assumptions, which are described in the following:

A TTSonset at 8 kHz hearing frequency was determined at a cumulative SEL (SELcum) of 175

dB re 1 µPa²s, corresponding to 1385 pile driving strikes of 145 dB re 1 µPa²s (SEL) in

30 minutes (Kastelein et al., 2016).

Single events below a certain SELSS never induce a TTS or affect recovery and are therefore

regarded as ‘effective quiet’ (Finneran, 2015; Ward et al., 1976). To date, no study has

determined an effective quiet threshold for harbor porpoises but the best estimate can be derived

from the lowest SELSS with the potential to induce a TTS, regardless of frequency or duration

(Finneran, 2015). The lowest determined SELSS with the potential to induce a TTS was

determined at 145 dB re 1 µPa²s (Kastelein et al., 2016). In the absence of an empirically

derived effective quiet threshold, we defined instead a threshold which is ‘still higher than

effective quiet threshold’ (SHEQ) as a proxy. A single strike sound exposure level of

145 dB re 1 µPa²s was defined as the SHEQ with the motivation to estimate a potential to cause

a TTS by means of an SELSS, which proved to induce a TTS after multiple reception, instead

of being conservative by considering all exposures. The implication of this is further discussed

in chapter A of the discussion. Pile driving strikes with SELSS below this SHEQ were therefore

excluded from the calculation of cumulative received levels. The SHEQ was used in

combination with the modeled sound propagation, to determine a ‘safe distance’, where SELSS

are below the SHEQ, and will not affect harbor porpoise hearing. The concept of the safe

distance should be understood as a novel approach to estimate hazard zones instead of a fixed



24

threshold. Further investigations are critically needed to determine an effective quiet threshold,

in order to replace the SHEQ, which is currently suggested as the best guess.

Data on the swim speed of harbor porpoises are rare due to their inconspicuous lifestyle and

poor accessibility. Only a few studies focused on the analysis of swim speed of harbor

porpoises. Maximum swim speed for animals in human care were determined at 4.3 m s-1 (Otani

et al., 2001) and in the wild at 4.3 and 6.1 m s-1 (Gaskin et al., 1974; Otani et al., 2000). A

maximum swim speed, derived from surfacing positions, was measured at 3.3 m s-1 for free-

ranging animals (Brandt et al., 2013a; Linnenschmidt et al., 2013). Mean swim speed of a free-

ranging harbor porpoise was determined at 0.9 m s-1 (Otani et al., 2000). An estimate of

maximum swim speed endurance has not been published to date. Assumptions on swim speed

are based on these available studies to cover a broad range of possible flight situations.

Accordingly, harbor porpoise flights were simulated at a swim speed of 0.9, 3.3, 4.3 and 6.1 m s-

1.

We selected a pulse interval of 1.3 s which was used in the study by Kastelein et al. (2015,

2016), where the TTSonset for multiple pile driving strikes was taken from and which also fits

well to the analyzed pile driving events. We assumed equal source levels for all pile driving

strikes and SELSS for a certain distance were treated as equal for the whole water column, since

the acoustic field was measured from bottom-mounted sound recorders only. The implication

of this is further discussed in chapter A of the discussion. All model assumptions are shown in

TABLE I.

TABLE I. Summary of variables and values used for the model.

Variable Assumption Value

TTSonset SELcum 175 dB re 1 µPa²s

Effective quiet SELSS 145 dB re 1 µPa²s

Safe distance Distance where SELSS is below effective quiet 5384 m

Swim speed Assumed to be constant 6.1, 4.3, 3.3, 0.9 m s-1

Pulse interval Time between pile driving strikes 1.3 s



25

D. Estimation of hazard zones

To estimate hazard zones, where a TTS can be induced by the reception of multiple pile driving

strikes, we defined a ‘safe distance’. At distances larger than the safe distance, SELSS are below

the SHEQ (Finneran, 2015; Ward et al., 1976) and will never induce a TTS or affect recovery,

no matter how many signals will be received. A safe distance was determined using the slope,

intercept and decay factor of the modeled sound propagation.

The received cumulative sound exposure level was calculated as the sum of all received single

strikes a harbor porpoise would receive on a simulated flight track, when swimming straight

away from the sound source up to the determined safe distance. Harbor porpoise positions on

the track were determined by steps with a length according to the given pulse interval of 1.3 s

and the swim speed of the porpoise, straight away from the sound source. The pulse interval

was derived from the analysis of underwater recordings. The expected porpoise position during

the kth pile driving strike, as a distance to the pile driving site (Rk) is thus

𝑅𝑘 = 𝑘𝑝𝑖𝑙𝑒 𝑠𝑡𝑟𝑖𝑘𝑒 × 𝑝𝑢𝑙𝑠𝑒 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙 × 𝑠𝑤𝑖𝑚 𝑠𝑝𝑒𝑒𝑑 + 𝑠𝑡𝑎𝑟𝑡𝑖𝑛𝑔 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (2).

SELSS values were calculated as a function of distance to the pile driving position and the

determined sound propagation for all simulated harbor porpoise positions on the flight track

using equation (1).

The received SELcum for the entire flight from a simulated start position up to a distance, where

SELSS is below the effective quiet threshold, can be obtained by

𝑆𝐸𝐿𝑐𝑢𝑚 = 10 × 𝑙𝑜𝑔10 ∑ 10(𝑆𝐸𝐿𝑆𝑆𝑘

10)

𝑛=𝑡𝑜𝑡𝑎𝑙 𝑛𝑜. 𝑜𝑓 𝑠𝑡𝑟𝑖𝑘𝑒𝑠

𝑘=1

[𝑑𝐵 𝑟𝑒 1 µ𝑃𝑎2𝑠] (3)

Based on the aforementioned equations we derived a closed-form solution for the received

SELcum for a fleeing porpoise (see results section). We verified this analytical solution by

simulating fleeing porpoises in which we iteratively summed up received levels of single

strikes. All analyses were performed and figures created using R (R Core Team, 2019).



26

III. Results

A. Sound propagation in the study area

A total of 912820 pile driving strikes were detected and analyzed in recordings with pile driving

activity. Inter-pulse intervals varied between 0.8 and 2.2 s. The most distinct inter-pulse interval

was found at 1.0 s, followed by 1.6 s (Ruser et al., 2016b), indicating that the fixed inter-pulse

interval in the simulation approach of 1.3 s was representative for actual pile driving activities.

Energy spectra of 76448 pile driving strikes from six monopiles at two measuring positions

were further analyzed. Most of the energy was found to be below 2 kHz with a peak around

160 Hz (FIG. 2). A further lower peak for frequencies around 5 kHz was also found for some

piles (ABW48, ABW59 in FIG. 2).

FIG. 2: Third octave level spectrum of the analyzed pile driving events, color and symbol coded

for measuring position and pile. Each mark on the line represents the determined median

SELSS for the corresponding center frequency of the third octave band. The median

ambient noise level of all analyzed 30 s recordings prior to pile driving activities is shown

as the lowest line with vertical lines representing the 1.5 interquartile range.



27

Received levels of single strikes (SELSS) ranged from 101.9 to 165.2 dB re 1 µPa²s at distances

between 2.4 and 36.8 km (see FIG. 3).

FIG. 3: Determined SELSS in dB (re 1 µPa²s) of pile driving activities during the construction

of 50 monopiles in the Amrumbank West OWF.Sound recordings were conducted at seven

static measuring positions. The median SELSS of all detected strikes per hour is marked by

points. Sound propagation was modeled by a non-linear regression (solid line), estimating

the intercept (200.5), slope (-13.64) and decay factor A (0.00078). The theoretical sound

propagation, assuming a damped cylindrical spreading with a received level of

160 dB re 1 µPa²s at a distance of 750 m is presented by the dashed line. The empirical

based best fit for the decay factor A was estimated at 0.0012 dB per meter, which is in line

with the empirical derived decay factors reported by Lippert et al. (2018) The number of

strikes within an hour is shown by color-coded points and its distribution is shown in the

histogram in the top right corner.

The received level (RL) was estimated by a non-linear logarithmic regression, estimating the

intercept, slope and decay factor A in dB per meter based on the determined median SELSS per

hour. We found

𝑅𝐿(𝑅𝑘) = 200.5 − 13.64 × 𝑙𝑜𝑔10(𝑅𝑘) + 0.00078 (𝑅𝑘) [𝑑𝐵 𝑟𝑒 1 µ𝑃𝑎2𝑠] (4) as the

best fit for the analyzed pile driving strikes over distance. The modeled sound propagation is



28

shown in FIG. 3 as a solid line. We used the number of pile driving strikes as a weighting factor

for the model. A median of 772 pile driving strikes per hour was found (sd=753, range 1-3586).

The SELSS at a distance of 750 m was estimated at 160.8 dB re 1 µPa²s.The number of strikes

within an hour is shown by color-coded points and its distribution is shown in the histogram in

the top right corner (FIG. 3).

The theoretical sound propagation, assuming a damped cylindrical spreading with a received

level of 160 dB re 1 µPa²s at a distance of 750 m is presented by the dashed line. The best fit

for the decay factor A was estimated at 0.0012 dB per meter, which is in line with the empirical

derived decay factors reported by Lippert et al. (2018). For distances up to 10 km the predicted

sound propagation and the theoretical sound propagation (Lippert et al., 2018; Zampolli et al.,

2013) showed high similarity. The theoretical sound propagation is not reliable for distances

further than 15 km.

B. Estimation of hazard zones

The calculation of the potential hazard zone for auditory damages was based on several

assumptions, which are described in Sec. II.

The potential to induce a TTS in harbor porpoises, which do not show a flight response, was

presented by showing the maximum radius where a TTS can be induced from multiple pile

driving strikes above the SHEQ. The hazard radius corresponds therefore to the determined safe

distance using the slope, intercept and attenuation factor of the modeled sound propagation

along with the effective quiet threshold. Therefore, we re-arranged equation (4) in order to

calculate a safe distance with a given received level, corresponding to the effective quiet

threshold. The rearrangement required the usage of the Lambert W function (Corless et al.,

1996) to solve the equation in which the unknown distance appears both outside and inside a

logarithmic function, leading to

𝑠𝑎𝑓𝑒 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 =

− {𝑠𝑙𝑜𝑝𝑒 × 𝑊 [−10

−𝑖𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡+𝑒𝑞𝑡𝑠𝑙𝑜𝑝𝑒 × 𝐴 × ln (10)

𝑠𝑙𝑜𝑝𝑒]}

𝐴 × ln (10) [𝑚] (5).

To calculate the safe distance, defined as a distance where the single strike level is

145 dB re 1 µPa²s, we inserted the intercept (200.5 dB), slope (-13.64 dB) and the attenuation



29

factor A (0.00078 dB m-1) of the determined logarithmic regression of the received levels into

this equation. The safe distance was determined at 5604 m.

According to an assumed pulse interval of 1.3 s, the SELcum would exceed the TTSonset of

175 dB re 1 µPa²s in 21.7 minutes within the area up to the safe distance. Animals located

within the area up to the determined safe distance at 5.6 km are estimated to suffer from a TTS

within a maximum of 21.7 minutes.

By a simulation approach, we determined the minimum distance a harbor porpoise must be

deterred prior to pile driving activities, to escape hearing impairment by a continuous flight up

to the assumed safe distance. Therefore, we modeled the total received SELcum for a complete

flight track from various start positions up to the safe distance at which the received SELSS was

below 145 dB re 1 µPa²s (SHEQ). Results were obtained for all possible start positions ranging

from zero to the safe distance. This simulation was conducted using the variables and their

specified values presented in TABLE I.

Thus, the received SELcum for the entire track of a harbor porpoise swimming straight away

from the sound source from an assumed position (start distance) up to the safe distance

(determined at 5604 m) can be obtained by

𝑆𝐸𝐿𝑐𝑢𝑚 = 10 × 𝑙𝑜𝑔 {10

𝑖𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡10

𝑝𝑢𝑙𝑠𝑒 × 𝑠𝑝𝑒𝑒𝑑×

𝐴 × 𝑙𝑛(10)

10

𝑠𝑙𝑜𝑝𝑒10

−1

× [𝛤 (1 −𝑠𝑙𝑜𝑝𝑒

10,𝐴 × 𝑙𝑛(10) × 𝑑𝑖𝑠𝑡. 𝑠𝑡𝑎𝑟𝑡𝑘

10)

− 𝛤 (1 −𝑠𝑙𝑜𝑝𝑒

10,𝐴 × 𝑙𝑛(10) × safe distance

10, )]} [𝑑𝐵 𝑟𝑒 1 µ𝑃𝑎2𝑠] (6).

For the received SELcum we find for 𝛤(𝑎, 𝑥) = ∫ 𝑡𝑎−1∞

𝑥 𝑒−𝑡 𝑑𝑡 as the upper incomplete gamma

function, giving an estimate for any transmission loss factor (slope) between cylindrical

(10×log10) and spherical (20×log10) spreading. To integrate the decay factor A, the incomplete

gamma function had to be included, which arises as a solution for certain integrals. We

calculated the received SELcum for all tested swim speeds with varying start distances

(dist.startk) ranging from 750 m up to the safe distance with equation (6) (see the R-script in

Appendix A).



30

Afterwards, we determined the minimum distance at which the TTSonset of 175 dB re 1 µPa²s

(Kastelein et al., 2016) was not exceeded. This distance was defined as the minimum distance

a harbor porpoise must be away from the pile driving site at the moment of the first strike to

reach the safe distance by a continuous flight before the cumulative energy can induce a TTS.

This distance was called the minimum deterrence distance.

Minimum deterrence distances are shown in TABLE II for simulated harbor porpoises

swimming away at four different speed levels. Assuming an immediate flight with 6.1 m s-1

after the first pile driving strike, harbor porpoises have to be further away than 2399 m from

the construction site to successfully prevent a TTS (FIG. 4, TABLE II).

TABLE II. Simulation results for the maximum distance as a start position for a flight, where a

TTS could still be induced before reaching the safe distance. Moreover, the number of

received strikes on the track from the minimum deterrence distance up to the safe distance

are given as same as the time of travelling in minutes. Simulation results are presented for

four swim speed levels.

Swim speed

in m s-1

Min. deterrence

in m

Strikes to safe

distance

Travel time to safe distance

in min

0.9 4659 807 17.5

3.3 3255 547 11.9

4.3 2897 484 10.5

6.1 2399 404 8.8

A harbor porpoise starting a flight at a distance of 2432 m with a constant speed of 6.1 m s-1

can still receive cumulative sound energy exceeding the TTSonset after 8.8 minutes of a

continuous flight and the reception of 405 pile driving strikes in that period. Harbor porpoises,

which are capable of fleeing at a speed of 4.3 m s-1, have to be more than 2897 m away from

the construction site to reach the safe distance before the received SELcum exceeds the TTSonset.

Slowly swimming harbor porpoises, traveling at a speed of 0.9 m s-1 can still suffer from a TTS

when starting a flight at the beginning of pile driving activities at a distance of 4659 m. Within

17.5 minutes, a harbor porpoise fleeing at 0.9 m s-1 could receive a cumulative SEL exceeding

the TTSonset after 808 strikes before reaching the safe distance.



31

FIG. 4: Simulation harbor porpoise fleeing from a certain start position (x-axis) up to the safe

distance (5604 m). The received SELcum for the complete flight track (y-axis) is color-

coded for each tested swim speed. The horizontal dashed line at 175 dB re 1 µPa²s

indicates the assumed TTSonset..

Single pile driving strikes are limited by legislation to a maximum of 160 dB re 1 µPa²s at a

distance of 750 m in Germany (FIG. 5, green circle). Underwater recordings revealed that up

to a distance of 5604 m, SELSS are high enough, to induce a TTS by multiple exposures (FIG.

5 red circle). We could show by means of a simulation that even harbor porpoises fleeing at a

constant speed of 6.1 m s-1 have to be deterred 2.4 km prior to the first pile driving strike to

successfully reach the safe distance before the TTSonset is exceeded by multiple exposures and

a TTS is likely.



32

FIG. 5: Radii of hazard zones around a pile driving site, where the TTSonset of 175 dB re 1 µPa²s

can be exceeded by multiple events above the SHEQ of 145 dB re 1 µPa²s for single strikes.

A TTS could be induced in harbor porpoises within 21.7 minutes at a distance up to 5.6 km,

if animals stayed within (outer circle). Harbor porpoises closer than 2.4 km could still

suffer from a TTS, even if fleeing immediately after the 1st pile driving strike with a swim

speed of 6.1 m s-1 (dashed middle circle). The distance of 750 m, where SELSS were

restricted to 160 dB re 1 µPa²s as a protective measure, is shown as the inner circle.



33

IV. Discussion

In this study, underwater sound recordings of real pile driving events were used in combination

with modeled sound propagation, swim speed and pulse intervals to estimate potential TTS

hazard zones for harbor porpoises. The transmission loss is strongly dependent on site-specific

parameters like frequency of sound, water temperature, salinity, depth, acidity, bottom type and

sea state (Marsh and Schulkin, 1962) and can often, even for single paths, not be extrapolated

to larger distances (Madsen et al., 2006). While the analysis of 912820 analyzed pile driving

strikes enabled us to model an accurate sound propagation within the research area, the

extrapolation of the results of this study to other areas should be made with great caution.

Source levels of pile driving strikes, applied noise mitigation systems and numerous physical

parameters of the acoustic field influence the sound propagation and frequency spectra of these

strikes, which are the driving factors for predicting potential hazard zones. We present a

comprehensive but also parsimonious model, which can easily be adjusted to other areas with

different sound propagation conditions or integrating updated variables.

As a novel approach, we considered an effective quiet threshold to classify areas where a TTS

can be induced by multiple exposures. Since we assume the same pulse interval and only

consider SELSS above the playbacks used in the study by Kastelein et al. (2016), we are

confident that the TTSonset is reliable or could be even lower when exposed to SELSS of higher

energy. Our simulation approach is, however, limited for predictions with pulse intervals, which

are higher than the assumed 1.3 s. The assumption that equal cumulative energy induces an

equal hearing shift is only valid for continuous fatiguing noises or for exposures with similar

duty cycles (e.g. Finneran et al., 2010a, 2010b, Kastelein et al., 2015b, 2014; Mooney et al.,

2009; Popov et al., 2014). Based on the analysis of underwater recordings from 50 monopiles

over a range from 2.4 and 36.8 km, we could show that noise levels are high enough to induce

a TTS by multiple exposures up to a distance of 5604 m.

A. Simulation results

In contrast to direct effects on hearing, behavioral reactions of free-ranging harbor porpoises to

pile driving strikes are not fully understood yet. Tagging of harbor porpoises with high

resolution sound and movement recording tags (DTAG, Johnson et al. 2009) allows for detailed

analysis of behavioral and physiological reactions on an individual basis. Tag-based studies

could show that vessel noise evokes clear behavioral responses in harbor porpoises, coinciding



34

with deeper dives, disturbance of foraging, increased fluke strike rates and cessation of

echolocation (Wisniewska et al., 2018b). Since we do not know how harbor porpoises could

react to pile driving noise, we simulated two different scenarios from the perspective of a wild

harbor porpoise exposed to pile driving noise: However, future research is needed to ascertain

their feasibility.

If the porpoise did not show a flight response and stayed inside the area where the noise levels

are high enough to induce a TTS by multiple exposures up to a distance of 5604 m, the received

SELcum would exceed the TTSonset anywhere within this area after 21.7 minutes at a pulse rate

of 1.3 s at the latest. Ecological reasons for staying within hazardous areas could be due to

strong inter-individual variability with animals not responding to that disturbance or tolerating

the noise if staying in an area is beneficial, for instance, because of high quality food. Staying

within a hazardous area could be either a result of natural decision-making or also caused by a

lack of information in which direction to swim. Sound source localization ability of harbor

porpoises has been found to be better for longer signals but has been tested for frequencies

above 16 kHz only (Kastelein et al., 2007). It has not been described whether harbor porpoises

are capable of localizing sound sources at such low frequencies and short duration like pile

driving strikes. The spectral content of sounds determines the ability to localize its origin

(Branstetter and Mercado III, 2006; Kastelein et al., 2005). Therefore, it is reasonable to assume

that localizing signals with higher frequency content is easier for harbor porpoises, like shown

for harbor seals, which are also underwater hearing specialists (Bodson et al., 2007).

Consequently, mitigated pile driving strikes could be even harder to localize, because bubble

curtains are more effective in mitigating frequency content above 1 kHz (Dähne et al. 2017,

FIG. 3).

In order to estimate potential hazard zones for harbor porpoises, which immediately flee after

the first pile driving event, we simulated the received SELcum for a complete flight track up to

the safe distance. We wanted to determine a minimum distance by this approach, a harbor

porpoise must be deterred prior to pile driving activities for in order to prevent a TTS, before

the TTSonset is exceeded. We could demonstrate that a harbor porpoise, which is within a radius

of 2.4 km to the pile driving site, cannot reach the safe distance before the TTSonset is exceeded

by the reception of multiple strikes. The simulated fleeing harbor porpoise received pile driving

strikes from behind. Although hearing in harbor porpoises is directional with better abilities for



35

signals ahead (Kastelein et al., 2005), our simulation is assumed to be valid. The receiving beam

of harbor porpoises is wider for lower frequencies (Kastelein et al., 2005) and the TTSonset was

derived from a study where harbor porpoises were exposed from varying positions while

swimming freely in a pool (Kastelein et al. 2015, 2016). Our simulation approach cumulates

multiple received pile driving strikes, which are equal to or higher than the SELSS used in a

playback experiment with animals in human care, in which a TTSonset was determined at 175 dB

re 1 µPa²s (Kastelein et al., 2016). Within that playback study, SELSS were the same throughout

the whole exposure. A fleeing harbor porpoise would, however, receive pile driving strikes with

decreasing SELSS with increasing distance to the sound source. In contrast to Kastelein et al.

(2016), the harbor porpoise would receive multiple strikes with variable SELSS, which are all

above the SELSS in that playback experiment. It is reasonable to assume that this could lead to

a lower TTSonset, because the TTSonset is dependent on the duty cycle, SPL and received SELcum

(Kastelein et al., 2015b, 2014b). However, a TTSonset for varying or decreasing SELSS over time

has not been determined yet.

Although effects of pile driving noise on harbor porpoise sightings and acoustic detections have

been described (Brandt et al., 2018; Dähne et al., 2013), behavioral reactions of harbor

porpoises regarding swim speed, echolocation behavior, diving depth and duration remain

unknown to date. In order to protect its hearing, harbor porpoises could flee close to the surface

or bottom, to benefit from interferences, mitigating received SELSS by reflections (Lloyd mirror

effect). This could be the case for described reactions of a harbor porpoise towards high levels

of vessel noise, which remained close to the bottom during highest levels of exposure

(Wisniewska et al., 2018b). The actual swimming depth of harbor porpoises within the hazard

area can highly change the received exposure level, which accordingly affects estimated hazard

zones. The modeled sound propagation has been derived from recordings of bottom mounted

underwater sound recorders, limiting the validity for predictions for the entire water column.

There are only few data available for the variability of received levels of pile driving strikes in

the water column. Received levels of pile driving strikes at distances between 3.8 and 14.6 km

from the pile driving source showed a depth dependency with a variability of up to 5.8 dB

between received levels at 1 and 13 m from the bottom (total depth 23 m, Gerdes et al. (2016)).

The received levels were highest at the bottom, decreased with distance to the surface and

displayed also a slight tendency for the level difference to decrease with increasing distance to



36

the pile (Gerdes et al. 2016). However, this limitation within the simulation approach has to be

reconsidered if more information on harbor porpoise reactions to pile driving noise is reported.

B. Application of evaluation tool

This study presents a novel approach to evaluating the impact of anthropogenic impulsive noise

on harbor porpoise hearing, by considering a distance where noise exposure does not affect

hearing anymore. Equation (6) can be applied to calculate the received cumulative SEL on a

flight up to the safe distance, and can be easily adjusted to different sound propagation

measurements. Furthermore, frequency weighting functions can be easily applied to the

TTSonset and the effective quiet threshold, if perceived loudness proves to be the best predictor

for auditory impairment (Houser et al., 2017; Kastelein et al., 2017; Southall et al., 2019;

Tougaard and Dähne, 2017). All presented simulations involve simplifications and assumptions

leading to non-negligible uncertainty in the estimated hazard zones.

As an example, we applied the formula to estimate hazard zones on reported SELSS of further

offshore wind farms in the German North Sea. Based on underwater recordings during the

construction of seven offshore wind farms in the German North Sea, average SELSS of 168 dB

re 1 µPa²s could be determined for noise mitigated pile driving events at a distance of 750 m

(Brandt et al., 2018). The SELSS of unmitigated pile driving strikes at a distance of 750 m was

determined at 175 dB re 1 µPa²s in the same study. The sound propagation determined by

Brandt et al. (2018) was very similar to the sound propagation modeled in this study. Using the

SELSS results of Brandt et al. (2018) for mitigated pile driving strikes and assuming the same

sound propagation as in this study, the safe distance would be at 10.4 km. The minimum

deterrence distance, derived from our simulation approach, would be between 6.6 and 9.4 km

for noise mitigated pile driving events, depending on swim speed. The safe distance for

unmitigated pile driving strikes would be at 15.8 km and minimum needed deterrent distances

ranged between 11.7 and 14.8 km, depending on swim speed. A clear deterrence effect was

found for SELSS above 143 dB re 1 µPa²s, reaching up to distances of 17 km (Brandt et al.,

2018). These findings are in line with the determined threshold at which harbor porpoises in

human care began to respond to pile driving playbacks with porpoising behavior (Kastelein et

al., 2013). These behavioral thresholds of about 145 dB re 1 µPa²s correspond to the assumed

SHEQ, which determines the safe distance and the lowest level of single strikes, which were

taken into account. The safe distance was determined at 15.8 km, whereas the deterrence range



37

was measurable up to 17 km (Brandt et al., 2018). Due to a high similarity in results, we assume

that the evaluation tool allows for a reliable prediction of potential hazard zones where a

temporary threshold shift can be induced by multiple pile driving strikes.

Although attempts are made to protect marine mammals from injuries worldwide, national

policies disagree in the definition of injury. While Germany considers a temporary threshold

shift as an injury, most other states define injury in the context of hearing as a permanent

threshold shift (e.g., U.S. Marine Mammal Protection Act in the United States). Recently,

updated noise exposure criteria have been proposed to predict the onset of auditory effects in

marine mammals (Southall et al., 2019). The SEL onsets are presented as weighted levels,

accounting for the frequency dependent effects in order to better meet perceived loudness of

the animal. The harbor porpoise belongs to the group of the very high frequency cetaceans

(VHF) in the recommended marine mammal noise exposure criteria (Southall et al., 2019). The

weighted onset was determined at 155 dB re 1 µPa²s for PTS and at 140 dB re 1 µPa²s for TTS.

In order to adopt these suggested PTS- and TTSonset thresholds in our simulation approach, the

SHEQ also has to be adjusted to the frequency weighting. The SHEQ is based on the playback

study by Kastelein et al. (2016), which were found to be 40 dB lower with applied frequency

weighting (Tougaard and Dähne, 2017, see table 1). Accordingly, the weighted threshold was

also decreased by 40 dB, down to 105 dB re 1 µPa²s.

Within the analysis of pile driving recordings in this study, frequency weighting was not

included in the project scope. Alternatively, published acoustic properties of pile driving strikes

recorded in the offshore DanTysk wind farm can be consulted (Dähne et al., 2017) to estimate

the potential to induce a PTS or TTS for a frequency-weighted sound propagation. A frequency-

weighted source level of 170 dB re 1 µPa²s was estimated from pile driving activities of 80

piles, measured at distances between 1 and 31 km, by fitting a simple transmission loss model

with 15×log10(R) and no absorption (Dähne et al., 2017). Accordingly, the calculated safe

distance extends to 21.5 km for this data-set, consisting of unmitigated, single- and double

bubble curtain-mitigated strikes. To escape a PTS, a minimum deterrence distance between 57

and 1155 m (TABLE III) would be needed for swim speeds between 6.1 and 0.9 m s-1, following

the criteria of Southall et al. (2019). The hazard zone where a PTS can be induced for fleeing

harbor porpoises extends to 1.2 km in the worst case scenario with a swim speed of 0.9 m s-1.

Regarding the reported effectiveness of previous deterrence (Brandt et al., 2013b, 2013a), a



38

PTS is assumed to be negligible. To escape a TTS with the same assumptions, a minimum

deterrence distance of between 4.5 and 7.6 km would be needed (TABLE III). However, the

minimum deterrence distances for weighted pile driving strikes from DanTysk are larger (2.3

and 6.5 km, TABLE III), compared to the unweighted results presented in this study.

Nevertheless, these also compare to the unweighted strikes reported in (Dähne et al., 2017).

These differences in potential hazard zones emphasize the need for a standardized risk

evaluation.

TABLE III: Application example of simulation approach, using the acoustic properties of pile

driving strikes reported by Dähne et al. (2017). The minimum deterrence for fleeing

harbor porpoises is simulated for the reported sound propagation of pile driving-strikes

from the construction work of the offshore wind farm DanTysk by using of the

recommended noise exposure criteria of Southall et al. (2019) and compared to the

unweighted threshold of Kastelein et al.(2016). The simulation results for the maximum

distance as a start position for a flight, where a TTS could still be induced before reaching

the safe distance, are presented for the potential to cause a PTS and TTS and for four swim

speed levels each.

Injury criteria Onset in

dB re 1µPa²s

Weighting function Swim speed

in m s-1

Min. deterrence

in m

PTS, Southall 155 (PTS) NOAAHF weighted 0.9 1155




TTS, Southall 140 (TTS) NOAAHF weighted 0.9 7548




TTS, Kastelein 175 (TTS) Unweighted 0.9 6509






39

C. Ecological relevance of disturbance

The TTSonset derives from a study, which determined a statistically significant TTS after

multiple exposure to pile driving playbacks, which was small and could only be measured due

to quiet experimental pools and low variability (Kastelein et al., 2016). However, a statistically

significant TTS does not inevitably mean it is ecologically significant. To date, it is still

unknown what the ecological effects of TTS are. Nevertheless, it is assumed that these are

related to the duration, affected frequency range and magnitude (Kastelein et al., 2017).

Potential consequences could be reflected in difficulties to hear in noisy environments. The

acoustical perception of the environment is of key importance for harbor porpoises when

navigating (Villadsgaard et al., 2007), finding and catching prey (DeRuiter et al., 2009;

Wisniewska et al., 2016) and for intra-specific communication (Clausen et al., 2010; Sørensen

et al., 2018) and any impairment could potentially negatively affect individual fitness,

reproduction or survival. Anthropogenic noise does not inevitably lead to individual mortality

but can affect the behavior of individuals causing sublethal effects (Pirotta et al., 2015). Noise

exposure can also lead to indirect mortality caused by stress responses, affecting physiology

(Aguilar de Soto et al., 2016; Wright et al., 2007). Effects can occur in various forms and can

therefore be interacting or cumulative (Kunc et al., 2016).

The here tested maximum swim speed of 6.1 m s-1 (Gaskin et al., 1974) probably overestimates

the average speed of harbor porpoises, determined as being between 0.7 and 2.2 m s-1

(Linnenschmidt et al., 2013; Otani et al., 2000) or between 1.3 and 3.2 m s-1 during flight

responses to seal scarer signals (Brandt et al., 2013a). Harbor porpoises in human care were

capable of maintaining an increased swim speed of 2 m s-1 throughout 30 minutes, when

exposed to pile driving playbacks with an SELSS of 145 dB re 1 µPa²s (Kastelein et al., 2018b).

The extent to which swim speed levels increase in wild animals is essential for predicting

energetic costs. The resulting drag from moving in a medium increases with the square of swim

speed and likewise the needed costs of locomotion for propulsion against the drag (Gallagher

et al., 2018; van der Hoop et al., 2014). Harbor porpoises live on an energetic knife edge, which

makes them particularly vulnerable to anthropogenic disturbance (Wisniewska et al., 2016).

Therefore, every extra needed food intake due to increased energetic costs and missed time for

foraging during a disturbance could have a severe impact.



40

Although there is no common EU regulation concerning noise mitigation during the

construction of offshore wind farms, wind farm industries are obliged in several European

countries to actively mitigate noise emission (Belgium, Denmark and Germany and the

Netherlands) or to restrict piling activities to designated time periods (Belgium, the

Netherlands). German legislation has enforced strictest regulations in the EU to date, by

determining a maximum single strike SEL of 160 dB re 1 µPa²s and a maximum SPL of

190 dB re 1 µPa at a distance of 750 m, obligatory deterrence of harbor porpoises prior to piling

activities and using a soft start procedure with limited force and longer pulse intervals. Our

analysis of the recorded pile driving strikes show that the protective measure of restricting

SELSS to 160 dB re 1 µPa²s in 750 m, in order to protect harbor porpoises from TTS by single

strikes, was respected. Additionally, this measure is very effective in reducing the potential

hazard zones, where a TTS can be induced by multiple exposures. We could show that

deterrence of at least 2.4 km prior to pile driving strikes is necessary to allow a flight of harbor

porpoises up to the safe distance before the TTSonset is exceeded. In order to deter harbor

porpoises, seal scarers are deployed prior to piling activities. The effective deterrence range of

a commercial seal scarer (Lofitech, Leknes, Norway) was measured as being 1.9 km by visually

observing surfacing positions (Brandt et al., 2013a). The available data within the piling

protocols concerning the soft start was incomplete. Neither the duration of the soft start nor the

pulse interval or used strike energy is regulated in Germany. In combination with the soft start

in the beginning of pile driving activities with restricted force and longer pulse intervals, this

previous deterrence could be sufficient to allow for a continuous flight up to the safe distance

at 5604 m before TTSonset is exceeded. However, effectiveness of deterrence effort has to be

monitored if all harbor porpoises should be protected. Only combining noise mitigation and

deterrence efforts within current regulations in Germany could be sufficient to enable harbor

porpoises to flee in time, but this has to be monitored for effectiveness. Deterrence should be

great enough prior to pile driving activities (minimum deterrence distance) to give harbor

porpoises sufficient time to flee to areas where no TTS can be induced. However, on the other

hand, it has to be as low as possible, to reduce temporary habitat loss.



41

D. Conclusion

Our approach to evaluating the potential for causing a TTS from multiple pile driving events

can be easily adjusted to different areas with other sound propagation characteristics.

Furthermore, it can be adjusted for other sound signals or species with different TTSonsets or for

an updated TTSonset if further studies are conducted, using variable SELSS for example. Our

simulations show that implemented measures during the construction of OWF in Germany

represent a valuable tool for protecting harbor porpoises not only from single but also from

multiple pile driving strikes. The deterrence prior to pile driving events is particularly important

and has to be monitored to give harbor porpoises sufficient time to leave hazardous areas at

moderate speeds. Based on our simulation approach, only the combination of restricting the

maximum SELSS to 160 dB re 1 µPa²s at a distance of 750 m, a previous deterrence and a soft

start with reduced energy and longer pulse intervals allow harbor porpoises to avoid a TTS from

multiple exposures. However, deterrence efficiency has to be monitored.

E. Acknowledgement

The underwater sound recordings for this study were obtained as part of the research carried

out during the projects “Impacts of underwater noise on marine vertebrates - Cluster 7” (Z 1.2–

53302/2010/14) and “Impact of underwater noise on marine mammals (UWE)” FKZ 3515 82

2000), funded by the Federal Agency for Nature Conservation (BfN). We would like to thank

Matthias Fischer and Max Schuster from DW-ShipConsult GmbH (Germany) for making and

analyzing underwater recordings and Dominik Nachtsheim for his support in generating

figures. We are very thankful for the proofreading of Frances Sherwood-Brock and her valuable

comments. We wish to express our gratitude to the legacy of Rodney Coates for awarding the

first author for the presentation of this study at the Effects of Noise on Aquatic Life Conference

in 2019 in The Hague (the Netherlands). Also we would like to thank the “Society of Friends

of the University of Veterinary Medicine Hannover (Gesellschaft der Freunde der

Tierärztlichen Hochschule Hannover e.V.” for funding the attendance of the first author at this

conference.



42

F. APPENDIX

R commands to calculate the safe distance and received SELcum on flight track

# Define base parameters

sheq <- 145 # effective quiet threshold

pulse <- 1.3 # interpulse interval

TTS_onset <- 175 # TTS onset for multiple exposure with pile driving strikes

slope <- -13.64 # slope of regression

intercept <- 200.5 # intercept of regression, estimated SL

A <- 0.00078 # attenuation factor in dB/m, absorption integrated

# calculate safe distance, where SELss is 145 dB, corresponds to equation (6) in manuscript

library(lamW)

safe_distance <-- (slope*lamW::lambertW0(-(10^((-intercept+sheq)/slope)

*A*log(10))/slope))/(A*log(10))

print(safe_distance) # 5604m

Rk <- safe_distance # calculate SELss for safe distance to cross check

SELss <- intercept+slope*log10(Rk)-A*Rk

print(SELss) #must be equal to sheq

# Calculate cumulative SEL for all received pile driving strikes on flight track up to the safe distance

# corresponds to equation (6) in the manuscript and results presented in table II

library(pracma)

dist.start <- 2399 #corresponds to minimum deterrence distance, SELcum must be equal to TTS onset

speed <- 6.1 #m/s, highest reported swim speed

max_sel_cum <- 10*log10(10^(1/10*intercept)/(pulse*speed)*(-1)*(A/10*log(10))^(-slope/10-

1)*(incgam(x=A/10*log(10)*safe_distance,a=1+slope/10)-

incgam(x=A/10*log(10)*dist.start,a=1+slope/10)))

print(max_sel_cum) # 175 dB re 1 µPa²s, TTS onset, minimum deterrence distance



43

# simulation with multiple swim speeds, generate results for table II

speed_all <- c(6.1,4.3,3.3,.9) # all simulated speed levels

for(s in 1:length(speed_all)){

speed <- speed_all[s]

hp.pos <- seq(from=750, by=speed*pulse, to = safe_distance) # harbor porpoise positions at

time of strikes

max_SEL_cum<-c()

for (i in 1:length(hp.pos)){

max_SEL_cum[i]<- 10*log10(as.numeric(sum((10^( (intercept+slope*log10(hp.pos)-

A*hp.pos) /10))[length(hp.pos):i])))

}

det <- (hp.pos[max(which(max_SEL_cum>TTS_onset))]) #minimum deterrence distance to

avoid TTS

strikes <-((safe_distance-det)/speed)/pulse #number of strikes

time <-((safe_distance-det)/speed) #time in s

print(c(det,strikes,time/60)) #results of table II

}

The use of seal scarers as a protective mitigation measure can induce hearing

impairment in harbour porpoises.

44

Published:

Reproduced from,

Schaffeld, T., Ruser, A., Woelfing, B., Baltzer, J., Kristensen, J.H., Larsson, J., Schnitzler,

J.G., Siebert, U. (2019). The use of seal scarers as a protective mitigation measure

can induce hearing impairment in harbour porpoises. Journal of the Acoustical

Society of America, 146 (6), 4288-4298, https://doi.org/10.1121/1.5135303

with the permission of the Acoustical Society of America.

Chapter 2: The use of seal scarers as a protective mitigation measure can induce

hearing impairment in harbour porpoises

45

Chapter 2: The use of seal scarers as a protective mitigation measure can

induce hearing impairment in harbour porpoises

T. Schaffeld1, A. Ruser1, B. Woelfing1, J. Baltzer1, J.H. Kristensen2, J. Larsson2, J.G.

Schnitzler1, U. Siebert1

1 Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine

Hannover, Foundation. Werftstr. 6, 25761 Büsum, Germany

2 Fjord&Bælt, 5300 Kerteminde, Denmark

This paper is part of a special issue on The Effects of Noise on Aquatic Life.

Abstract

Acoustic deterrent devices (ADDs) are used to deter seals from aquacultures but exposure of

harbour porpoises (Phocoena phocoena) occurs as a side-effect. At construction sites, by

contrast, ADDs are used to deter harbour porpoises from the zone in which pile driving noise

can induce temporary threshold shifts (TTSs). ADDs emit such high pressure levels that there

is concern that ADDs themselves may induce a TTS. A harbour porpoise in human care was

exposed to an artificial ADD signal with a peak frequency of 14 kHz. A significant TTS was

found, measured by auditory evoked potentials, with an onset of 142 dB re 1 lPa2s at 20 kHz

and 147 dB re 1 lPa2s at 28 kHz. The authors therefore strongly recommend to gradually

increase and down regulate source levels of ADDs to the desired deterrence range. However,

further research is needed to develop a reliable relationship between received levels and

deterrence.



46


A.R. and U.S. were involved in designing the project and grant acquisition. The experimental

design was developed by A.R. with support of T.S. The experiments with the harbour porpoise

in human care were conducted by T.S. and A.R.. The animal was trained by J.H.K and J.L.,

who also monitored and instructed the animal during the experiments. T.S. analysed the data

with support from A.R. and J.S. T.S. was supervised by A.R., J.S. and U.S. The manuscript was

written by T.S.. All authors provided critical feedback and helped to shape the research, analysis

and contributed to the final version of the manuscript.



47

I. Introduction

Acoustic deterrent devices (ADDs, e.g. seal scarers) are applied in two different scenarios.

These devices are mainly applied to deter seals from fish farms with the aim to prevent

economic loss, due to seal depredation and damage to fishing gear. In European areas with

extensive fish farms (e.g. along the west coast of Scotland), ADDs are a chronic source of

anthropogenic noise pollution (Findlay et al., 2018). Coastal areas where aquacultures are

located, are a typical habitat of harbour porpoises (Phocoena phocoena) (Brandt et al., 2018;

Findlay et al., 2018; Gilles et al., 2016; Hammond et al., 2017; Peschko et al., 2016; Viquerat

et al., 2014). Harbour porpoises have a very wide hearing range and are capable of hearing seal

scarer signals (Kastelein et al., 2002; Ruser et al., 2016a). While ADDs show highly varying

success in seal deterrence (Götz and Janik, 2013) and could even attract animals, harbour

porpoises exhibit strong avoidance reactions (Mikkelsen et al., 2017). The much further

deterrence of harbour porpoises occurs as an unwanted side effect in cases where ADDs are

deployed to deter seals from fish farms (Brandt et al., 2013a).

The second scenario of ADD application is the use as a deterrent device prior to pile driving

activities in offshore wind farms with the aim to deter harbour porpoises as a target species.

Offshore wind farm construction is substantially increasing in Europe, providing a promising

alternative to fossil fuels and nuclear power. In total, 92 offshore wind farms have been

constructed to date in 11 European countries including sites with partial grid connection,

amounting to 4,149 connected wind turbines (Remy and Mbistrova, 2018). The majority of

wind turbines are bottom mounted. High levels of impulsive noise arise, when piles are driven

into the seabed (Bailey et al., 2010; Brandt et al., 2018; Tougaard et al., 2009). The increasing

human encroachment which accompanies the construction of offshore wind farms has negative

effects on key ecological species such as the harbour porpoise (Brandt et al., 2013b, 2018;

Dähne et al., 2013; Tougaard et al., 2009), which inhabits coastal areas.

Due to its high sensitivity towards anthropogenic noise, the harbour porpoise can be regarded

as an indicator species in noise impact evaluations (Southall et al., 2007; Tougaard et al., 2015).

Harbour porpoises face the risk of a temporary hearing impairment, if they stay in areas close

to the pile driving site, since impulsive noise has the potential to induce a temporary threshold

shift from single (Lucke et al., 2009) or multiple exposure (Kastelein et al., 2015a, 2016).

Implementation of noise exposure criteria into national legislation differs between countries



48

(Stöber and Thomsen, 2019). In particular, injury is defined differently between national

policies (e.g. by the Habitats Directive in Europe or by the U.S. Marine Mammal Protection

Act in the United States). In Germany, a temporary loss of hearing after the exposure to pile

driving noise (temporary threshold shift, TTS) is considered as an injury (BMU 2014), whereas

most other states in Europe or in the United States only regard a permanent threshold shift

(PTS) as an injury. Harbour porpoises are protected throughout Europe and are listed in Annex

II and IV of the European Union Habitats Directive (Council Directive 92/43/EEC on the

Conservation of natural habitats and of wild fauna and flora).

Although several countries established criteria frameworks, which define limits for hearing

impairments, regulations pertaining to the use of deterrent devices differ between countries

(reviewed for Germany, Denmark and United States in Stöber and Thomsen (2019). In German

waters single strike sound exposure level (SELSS) of 160 dB re 1 µPa²s and a peak pressure

level (Lp) of 190 dB re 1 µPa must not be exceeded at a distance of 750 m to the pile driving

site (BMU, 2014). In order to prevent physical damage harbour porpoises must be deterred from

the near-field, where sound exposure thresholds can exceed the threshold (BMU, 2014).

Following German legislation, permissions for offshore wind farm constructions generally

include the condition to deter harbour porpoises prior to pile driving activities (BMU, 2014).

ADDs are regularly applied as a tool to deter harbour porpoises prior to pile driving activities

(Brandt et al., 2018). ADDs emit signals between 10 to 40 kHz, corresponding to the range of

best under water hearing in seals (Kastak and Schusterman, 1998; Kastelein et al., 2009b,

2018a; Reichmuth et al., 2013), at very high source levels up to 193 dB re 1 µPa (Lepper et al.,

2004). Seal scarer signals leads to deterrence effects in harbour porpoises, measured by

surfacing distance to sound source (Brandt et al., 2013a; Mikkelsen et al., 2017), aerial surveys

(Brandt et al., 2013b) or by echolocation activity (Brandt et al., 2013b).

The aim of this study was to test, whether a seal scarer has the potential to induce a TTS in

harbour porpoise hearing. Additionally, we determined the threshold distance, at which single

exposures to seal scarer signals can induce a TTS, in order to estimate hazard zones for seal

scarers. We provide critically needed information to develop protective measures, which ensure

both, sufficient deterrence and the avoidance of hearing impairment inflicted by ADD signals.



49

II. Material & Methods

A. Study area and animal subject

All measurements were conducted at the Fjord & Bælt centre in Kerteminde (Denmark). One

harbour porpoise was kept in the 36×15 m semi-natural outdoor enclosure during this study.

The enclosure was constructed of nets with a mesh size of 10 cm², allowing for a natural flow

of seawater from the Kerteminde Fjord and the Great Belt. Water depth within the enclosure

varied between three and four meters, depending on position and tide. Measurements were

conducted in a 6×4×1.9 m floating holding pool. A gate on one side was always open, allowing

the animal to leave whenever it wanted. The study subject was a female harbour porpoise born

in 1995, which has been kept in human care at Fjord & Bælt since 1997, after it was rescued

from a pound net.

The harbour porpoise is kept under human care by the Fjord&Bælt in Kerteminde (DK) under

permit no. SVANA-610-00084 from the Danish Ministry of Food, Agriculture and Fisheries.

All trials were conducted adhering to the respective ethical principles as well as to the relevant

international and national guidelines for animal experiments and under constant supervision of

experienced biologists animal trainers. Experienced animal trainers monitored animal condition

and signs of stress of the animal throughout all experiments. The harbour porpoise has been

trained two times a day through standard operant conditioning and positive reinforcement

techniques by a team of professional animal trainers. Trials were only conducted, if visibility

allowed for observing the harbour porpoise underwater at the bite plate throughout the whole

experiment. During all exposure sessions, the animal was visually observed by the trainer from

above and additionally recorded by an underwater camera. In case of an observed stress

response the experiments would have been stopped immediately.

B. Background noise recordings

Vessels passing close to the enclosure increased background noise levels, since the semi-natural

enclosure was solely separated from the harbour of Kerteminde by nets. Therefore, background

noise was continuously monitored during measurements. Experiments were only conducted, if

no vessel was passing by or no other unwanted noise source was present. Background noise

was recorded using a custom-made software application (LabVIEW, USA) with a hydrophone

(TC4032, Reson Teledyne, DK), pre-amplified by 20 dB (ETEC amplifier, DK) and band pass

filtered (100 Hz-180 kHz, ETEC 1501, DK). Recordings were digitized with a data acquisition



50

card (NI USB 6251, National Instruments, USA) sampling at 400 ksamples s-1 and at a 16 bit

resolution.

C. Experimental procedure to measure hearing thresholds

Hearing thresholds were measured by monitoring the auditory evoked potential (AEP)

response, a commonly used non-invasive electrophysiological technique (Finneran, 2018;

Nachtigall et al., 2017; Ruser et al., 2016a). In principle, a hearing stimulus (1) is presented to

the test individual. If the acoustic stimulus is above threshold levels, the neurons within the

acoustic pathway are stimulated and the neuronal discharges can be detected by electrodes

placed on the head (2).

1. Hearing test stimulus

Hearing thresholds of the animal were determined at 20 and 28 kHz. Short tones centred at

these frequencies were emitted, while auditory evoked potentials of the brainstem were

simultaneously recorded. A rugged notebook (Panasonic Toughbook CF30) computer was used

to digitally generate stimuli, which were converted to analogue by a USB multifunction data

acquisition card (NI USB 6251, National Instruments, USA). The stimuli were updated at a

1 MHz rate with a 16 bit resolution and band pass filtered (100 Hz-250 kHz, 24 dB/octave,

Krohn Hite, USA) before emission by the transducer. The generated stimuli were emitted by a

TC4033 transducer (Teledyne Reson, DK), placed at depth of 0.8 m and a distance of 1 m in

front of the animal. Generated stimuli consist of 1024 tone pips for each tested sound intensity.

Each pip consists of two sine rise, one sines steady and two sines fall, with an epoch length of

17 m s (FIG. 6). Accordingly, the exposure per tested sound pressure level (SPL) had a duration

of 17.4 s.

The targeted maximum dive duration of 40 s allowed for testing two different SPL values per

dive. All playbacks of hearing test stimuli and recordings of auditory evoked potentials were

conducted with a custom written software (Evoked Response Study Tool, EVREST, (Finneran,

2009; Finneran et al., 2008). Received SPL of test stimuli were calibrated by averaging 1024

stimuli prior to each trial at an SPL of 111 dB re 1 µPa with a TC4013 hydrophone (Teledyne

Reson, DK) placed at the bite plate, close to the position of the porpoise during stimulus

presentation. Recorded stimuli signals were pre-amplified by 60 dB (ETEC amplifier, DK),

band pass filtered from 1 to 180 kHz (ETEC B 1501, DK) and then digitized at 500 kHz with a

16 bit DAQ-card (NI USB 6251, National Instruments, USA).



51

FIG. 6: Tone pips, used as hearing stimuli. A) Section with ten tone pips out of a complete train

consisting of 1024 repetitions. B) Detail view of one pip (five cycles of 20 kHz carrier)

within the pip train. C) Frequency spectra of the 20 and 28 kHz tone pips with -3 dB

bandwidth levels (grey horizontal lines).

2. Brain potential acquisition and hearing sensitivity assessment

Auditory evoked potentials were measured using 10 mm silver-plated electrodes, imbedded in

suction cups, which were gently attached to the body surface along with standard conductive

gel, which is regularly used in human electroencephalography (EEG) recordings. Small

electrical charges, generated by the brain in response to the acoustic stimuli could be measured

by placing the active (+) electrode behind the blowhole, the inverting electrode (-) along the

dorsal midline of the porpoise between the blowhole and dorsal fin and the ground electrode

(⏚) on top of that suction cup. Impedance between electrodes was tested with an impedance



52

meter (Temec Instruments BV, NL) to ensure that impedance was <3 kOhm during all

measurements. Electrodes were connected with 10 m long shielded cables to a bio-potential

amplifier (CP511, GRASS Technologies, USA) in order to amplify (+100 dB) and filter (0.3-

3 kHz bandpass filter) the measured voltage between the inverting and non-inverting electrodes.

The signal was digitized at 50 kHz and 16 bit resolution by the data acquisition card, connected

to the computer. AEPs were recorded with the custom-made software (EVREST) that was also

used to emit stimuli.

3. Experimental set up

First, the animal had to get accustomed to wear suction cups on the skin. Suction cups contained

silver-plated electrodes, which were attached via cables to the computer. Second, the animal

was trained to dive to a bite plate at a depth of 0.8 m and be stationary.

Two separate stations, approximately 4 m apart at the right and left corner of the holding pool

were used for the trials. Both bite plates were positioned at a fixed distance of 1 m to the

projecting transducer. At the left bite plate, the animal could be exposed to the fatiguing sound,

hearing tests were conducted solely at the right bite plate. Each trial to determine a hearing

threshold included four dives to the bite plate, each lasting 40 s. During a dive, two different

sound amplitudes could be tested, allowing for testing eight intensities in four dives. Sound

amplitude started at 80 dB re 1 µPa [root-mean square (rms)] for baseline measurements and

was increased by the EVREST software internally in steps of 5 dB up to 120 dB re 1 µPa (rms).

D. Fatiguing stimulus and experimental procedure

We aimed at testing, if seal scarer signals can induce a temporary hearing shift in harbour

porpoises. Therefore, we exposed the animal to artificial seal scarer signals at a range of sound

exposure levels and tested, if post-exposure hearing thresholds differed from baseline hearing

thresholds. One complete session consisted of three trials, which were conducted on the same

day. Three trials were needed to determine 1) the pre-exposure baseline hearing at experimental

day, 2) the post-exposure hearing and 3) the recovery. In trials 1 and 3 a hearing threshold was

determined as described, whereas prior to trial 2, the animal was exposed to a fatiguing

stimulus. During all exposure sessions, the animal was visually observed by the trainer from

above and additionally recorded by an underwater camera.

In all trials, the harbour porpoise was first sent to the exposure station, at the left bite plate. The

animal stayed there upon receiving an acoustic signal from the trainer. For the baseline hearing



53

or recovery measurements, the animals was not exposed, but prior to exposure trials, the animal

received a fatiguing stimulus, while staying at the bite plate. To allow for a complete recovery

of the hearing system before the next trial the animal was exposed only once a day. Recovery

measurements of the hearing thresholds took place two hours after exposure to the fatiguing

stimulus.

We exposed the animal to an artificial seal scarer signal, comparable to a Lofitech (Lofitech

AS, Leknes, Norway) seal scarer as fatiguing stimuli. This artificial seal scarer signal was built

following Lofitech seal scarer signals, recorded at a distance of 130 m (Brandt et al., 2013a).

The main frequency component of the 0.5 s signal was set to 14 kHz and four harmonics (28,

42, 56 and 70 kHz) with gradually decreasing sound levels were added. The artificial signal

was generated in R (R Core Team, 2019), using the package ‘seewave’ (Sueur et al., 2008). The

stimuli level of each frequency component was calibrated before the first exposure of this study,

meeting the gradually decreasing components in Brandt et al. (2013). The same signal was used

for all exposures within this study.

Initially the fatiguing sound were presented at very low exposure levels and then subsequently

increased by a maximum of 3 dB between days. The signals were transmitted by an ITC-1001

transducer (International Transducer Corporation, USA). A power amplifier (PA1001, ETEC,

Dk) was used to increase sound energy emission in steps of 3 dB. Signals were amplified

(PA1001, ETEC, DK) and recorded at the bite plate with a TC4013 hydrophone (Reson

Teledyne, DK), pre-amplified by 40 dB (ETEC-B, 1501 amplifier, DK) and bandpass filtered

with a passband from 1 to 180 kHz. Fatiguing stimuli were played back by a custom written

software (LabVIEW, USA), which was also used for background recordings. The sound

exposure level (SEL) was determined using this software. The frequency spectrum of the

artificial seal scarer signal, used as a fatiguing stimulus on October 18th, is presented in FIG. 7.



54

FIG. 7: Recorded frequency spectrum of one generated artificial seal scarer signal (top), which

was used for animal exposure. The STFT of the recorded signal (bottom) shows the peak

frequency of the seal scarer signal at 14 kHz with 4 octave overtones. Porpoise clicks

around 130 kHz were recorded prior and after exposure. Overlap=87.5%, window

length= 1048 samples.

In further analysis, recordings of seal scarer exposures were additionally frequency weighted,

adjusting the signal to perceived loudness, based on the harbour porpoise hearing spectra. We

used the proposed NOAAHF (National Oceanic and Atmospheric Administration) frequency

weighting, which has been recommended to evaluate effects of underwater noise on the hearing

of marine mammals (National Marine Fisheries Service, 2018; Southall et al., 2019). Frequency

weighting of raw wav recordings has been conducted by the recently published MATLAB

(MathWorks, USA) function ‘NOAAweighted’ (Tougaard and Beedholm, 2018). Within the

recommended Marine Mammal Noise Exposure Criteria Southall et al. (2019) refer to this same

weighting function as ‘very high frequency cetaceans’. The SEL was determined afterwards by

the same software used for the playback of fatiguing sounds.



55

E. TTS definition

All hearing thresholds with no prior exposure were used to determine the baseline. Due to the

small sample size of baseline measurements at 28 kHz, we included hearing thresholds, which

have been measured 2 h post-exposure, in recovery trials. These two events have been tested

by a Welch two sample t-test for unpaired samples for differences compared to the 8 baseline

measurements. The thresholds measured in recovery trials did not show significant differences

from the baseline trials. Therefore hearing thresholds at 28 kHz measured in the recovery trials

were pooled with the baseline measurements. This pooling is assumed to be conservative in the

detection of a TTS, since only higher and no lower hearing thresholds are expected in the post-

exposure trials. The baseline-hearing threshold was defined as the mean of all these trials. Post

exposure threshold measurement procedure was the same as for baseline hearing trials. Hearing

thresholds were measured immediately after exposure and were gathered in an interval of 1 to

8 minutes after exposure. Using the mean hearing threshold and its standard deviation, we

obtained the threshold for a significant hearing shift (p=0.05). A temporary threshold shift was

defined as a hearing threshold exceeding the mean threshold by 1.65 × the standard deviation

(p=0.05, one-sided test). A typical TTS definition is a hearing thresholds 6 dB above the

baseline (Southall et al., 2019). However, this threshold is based on the smallest shift, which

was clearly distinguishable due to the variability of 3-4 dB in baseline measurements in the

study of Schlundt et al.( 2000). Although we follow the TTS definition, as a significant shift

from baseline hearing (see e.g. Finneran et al. (2005); Kastelein et al. (2014b, 2016)), the 6 dB

criterion onset can be obtained from the provided TTS regression.



56

F. Data analysis

Data recorded by the electrodes was first checked for quality, in order to exclude obvious

disturbances, which can be produced by environmental effects (waves, rain) or technical

problems (crosstalk between cables). Recorded signals with peak voltages above 20 µV were

rejected, in order to exclude myogenic artefacts with large amplitudes, originating from

movements or respiration of the animal. Data were post-processed with a digital Butterworth

bandpass filter of 8th order, to get a clean signal between 0.3 and 3 kHz. To objectively

determine, if stimuli at a certain SPL could be heard by the animal, we tested if the recorded

brainstem signal differed from background noise within the recordings by a single point F-test

(Don et al., 1984; Elberling and Don, 1984). This method uses a variance analysis in

determining the ratio of the magnitude of the ABR to the estimated averaged background noise.

Afterwards, all responses were verified by two trained assessors, searching for stereotypic

patterns manually. The stereotypic wave V in an auditory evoked potential has been proven to

have a significant relationship to loudness (Serpanos et al., 1997) and therefore served as an

indicator for sound perception. A signal was determined as perceived (“hit”), if wave V was

determined in a time window of 3.8 to 5.2 ms after exposure. If no wave V was found the signal

was determined as “miss”. Hearing thresholds were defined as the mean SPL of the lowest “hit”

and the highest “miss” (FIG. 8). All analyses were conducted and figures created with R

Studio(R Core Team, 2019).



57

FIG. 8: Example of measured AEP for 8 sound pressure levels (colour coded) between 87 and

122 dB re 1 µPa. Data was recorded after an exposure to a seal scarer signal with an SEL

of 147.3 dB re 1 µPa²s. The dashed black vertical lines indicate the time window, where

the wave V was searched. The post-analysis with the single point F-test and visual

screening of two experienced assessors determined the lowest “hit” at a SPL of

97 dB re 1 µPa and the highest “miss” at 92 dB re 1 µPa. The hearing threshold was

determined in the middle of these values and corrected for the results of the SPL

calibration (-5.3 dB), resulting in a threshold of 89.2 dB re 1µPa. The vertical black line

in the top-left corner represents the voltage scale.



58

III. Results

A. Baseline hearing thresholds

Baseline hearing at 20 kHz was measured on 25 days (see TABLE V in APPENDIX), resulting

in a mean baseline hearing threshold of 90.0 dB re 1 µPa ± 3.7 dB. An inspection of quantile-

quantile plots verified, that baseline hearing thresholds were normally distributed and a critical

value (p<0.05) of 96.1 dB re 1 µPa was obtained. Therefore, a hearing shift higher than 6.1 dB

was regarded as a significant hearing elevation.

Baseline measurements for stimulation at 28 kHz were conducted on 6 days, resulting in 10

measurements (appendix A). Since the measurements of baseline and recovery sessions were

not significantly different (p=0.9713), pre- and post-exposure hearing thresholds were pooled

to determine a baseline hearing threshold for 28 kHz. The mean baseline hearing threshold was

85.4 dB re 1 µPa ± 2.9 dB. An inspection of quantile-quantile plots verified, that baseline

hearing thresholds were normally distributed and a critical value (p<0.05) of 90.4 dB re 1 µPa

was obtained. Therefore, a hearing shift higher than 4.8 dB was regarded as a significant hearing

elevation.

B. Post-exposure thresholds

The harbour porpoise showed an aversive reaction to the presentation of the fatiguing stimulus

in almost all cases with an exposure exceeding 143 dB re 1 µPa²s. It consisted of a short

backward movement without leaving the bite plate. This reaction could represent the acoustic

startle reflex, which mirrors the audiogram 80-90 dB above the hearing threshold (Pilz et al.,

1987). Acoustic signals with a short rise time can elicit an oligo-synaptic reflex arc in the

brainstem, provoking the contraction of refractor muscles (Koch and Schnitzler, 1997). This

reaction did not occur during all trials. The harbour porpoise stayed at its position until it was

called back by the trainer during all exposure sessions.

For hearing tests at 20 kHz, exposure trials were conducted on 9 days with sound exposure

levels between 137.6 and 157.5 dB re 1 µPa²s. In 5 trials a significant temporary hearing shift

was measured at 20 kHz, as the post-exposure threshold was above 96.1 dB re 1 µPa, which

was determined as the critical value for a TTS at 20 kHz. Calculating linear regression for these

determined hearing shifts, we obtained a TTSonset at a sound exposure level of

141.8 dB re 1 µPa²s (FIG. 9).



59

Post-exposure hearing at 28 kHz was tested in 5 trials with sound exposure levels from 146.9

to 155.6 dB re 1 µPa²s. In 4 trials a significant TTS, defined as a hearing threshold above

90.2 dB re 1 µPa, could be measured at 28 kHz. We inferred a TTSonset at a SEL of

146.9 dB re 1 µPa²s , using linear regression (FIG. 9).

We obtained a SPL-TTSonset for each SEL-TTSonset by a linear regression of measured SPL and

SEL (see APPENDIXFIG. 11Appendix C). NOAAHF weighted TTSonsets were derived from the

calculated regression of frequency weighted exposure recordings and the determined TTS (see

FIG. 12 in Appendix D). All results are summarized in TABLE IV.

FIG. 9: Effects of seal scarer exposure (at 14 kHz, with four harmonics) on hearing thresholds

at 20 (black circles) and 28 kHz (grey triangles). Filled symbols indicate a significant shift

from baseline hearing, which was determined at >6.1 dB for 20 and >4.8 dB for 28 kHz.

Unfilled symbols indicate hearing thresholds, which were not significantly shifted after

exposure. A linear regression for each hearing frequency, using only exposures which led

to a TTS, was calculated in order to estimate the TTSonset. The 95 % confidence intervals

are shown by dashed lines. The TTSonset at 20 kHz was determined at 141.8 and at 28 kHz

at 146.9 dB re 1 µPa²s.



60

TABLE IV. Summary of the determined TTSonset after exposure to artificial seal scarer signals.

The signal consisted of a 14 kHz tone, with four harmonics. Hearing thresholds were

measured at 20 and 28 kHz. TTSonsets were determined for unweighted and auditory based

NOAAHF (National Oceanic and Atmospheric Administration; National Marine Fisheries

Service, 2016) weighted exposures.

Frequency

kHz

Weighting Intercept slope SEL-TTSonset

dB re 1 µPa²s

SPL-TTSonset

dB re 1 µPa

20 - -81.7 0.6 141.8 155.2

20 NOAAHF -78.9 0.6 138.4 152.9

28 - -103.9 0.8 146.9 160.3

28 NOAAHF -136,6 1.0 143.6 157.4

IV. Discussion

A. Application of Seal Scarers

Acoustic deterrent devices are widely used, for instance to counteract the economic loss by seal

depredation in aquacultures. Within the past 30 years the worldwide farming of finfish species

has substantially increased (FAO, 2018; Findlay et al., 2018) and so has the economic loss by

seal depredation. These sites represent an easily accessible food source with a high profitability,

if no anti-predator control methods are applied. Although ADDs are extensively applied where

fish farms exist in Europe, e.g. along the west coast of Scotland, no official statistics exist on

the number, types and duration of ADD usage (Findlay et al., 2018). Furthermore, its deterrence

efficiency is highly variable and may also decrease over time, due to habituation (reviewed in

Götz and Janik, 2013).

In contrast to seals, harbour porpoises show strong avoidance behaviour to ADDs (Brandt et

al., 2013a; Mikkelsen et al., 2017; Olesiuk et al., 2002). Seal scarer operators should be aware,

that the behavioural manipulation of seals as a target species, might also affect non-target

species, which is widely overlooked, when ADDs are applied around aquacultures. The rather

unspecific signals of seal scarers are not specifically tuned to the auditory abilities of seals.

Areas where aquacultures are located, regularly overlap with harbour porpoise occurrence

(Findlay et al., 2018). Harbour porpoises are especially sensitive for underwater noise (Southall

et al., 2019). For the case of fish farms, harbour porpoises (Phocoena phocoena) are regarded

as a non-target species because there is no evidence that these animals feed on farmed fish or

damage fishing gear (Götz and Janik, 2013). The strong reactions of harbour porpoises to ADDs



61

have been exploited in other applications, such as a deterrent device prior to pile driving

activities with the aim to prevent hearing impairment from the high noise levels of pile driving

strikes. Indeed, a far reaching avoidance behaviour occurred up to distances of 7.5 (Brandt et

al., 2013b) or even 12 km (Dähne et al., 2017). Although the exploitation of renewable energy

represents an important component towards a more environmentally friendly power production,

impacts on marine fauna, caused by anthropogenic noise during and prior to the construction

have to be considered.

B. Effect on harbour porpoise hearing

Caution is required when using deterrent devices with high source levels for both, the

application around fish farms and as deterrent devices to prohibit TTS from pile driving strikes.

We could show that these signals itself have the potential to induce a significant temporary

hearing shift in a harbour porpoise both at 20 and 28 kHz hearing frequency. Harbour porpoises

critically rely on hearing to navigate (Villadsgaard et al., 2007), find and catch prey items

(DeRuiter et al., 2009; Wisniewska et al., 2016) and communicate (Clausen et al., 2010;

Sørensen et al., 2018). Disturbance effects arise from numerous sources in addition to noise

pollution (Andreasen et al., 2017; ASCOBANS, 2002, 2012; Beineke et al., 2005; Jepson et al.,

2016; Knoop and Müller, 2009; Mahfouz et al., 2014; Reeves et al., 2013). Affected hearing

can influence the survival rate of single individuals (Mann et al., 2010; Morell et al., 2017a).

Disturbance effects may even result in decreased individual fitness and could lead to long-term

population consequences (King et al., 2015).

Although the experiments were conducted in a semi-natural enclosure with a sound field that

we could not control, the measured TTS was most likely induced by the exposure of the seal

scarer signal only. While passing vessels can lead to behavioural reactions of harbour porpoises

(Dyndo et al., 2015; Wisniewska et al., 2018b), there is no evidence for the potential to induce

a TTS by this continuous noise source. Experiments were only conducted in the absence of

anthropogenic noise. Therefore, we can exclude the possibility that the induced TTS derived

from another noise source than the seal scarer signal.

The pre-exposure baseline hearing threshold at 20 kHz is about 40 dB higher than measured by

Kastelein et al. (2010). This difference is substantially caused by differences in the applied

methods to measure hearing thresholds. Using psychophysical techniques instead of AEP

measurements can lead to thresholds, which are 1 – 31 dB lower (Mulsow and Reichmuth,



62

2010). Hearing thresholds of wild harbour porpoises from the Inner Danish Waters, which have

been determined by AEP measurements are about 10 dB lower (Ruser et al., 2016a) than the

baseline hearing of this study at 20 kHz. Our data derives from one animal, at a senior age of

23 years, in a semi-natural enclosure restricted by nets from the harbour solely, but is still within

the 1.5 interquartile range of wild harbour porpoise hearing thresholds (Ruser et al., 2016a).

We tested the effect of the artificial sear scarer signal on harbour porpoise hearing at 20 kHz,

although the main frequency component of the fatiguing stimulus was at 14 kHz, which is

~0.5 octaves below. This was due to technical difficulties in measuring hearing thresholds

below 20 kHz in the semi-natural environment and with this certain animal. The hearing

threshold at 28 kHz is at the frequency of the first harmonic of the artificial seal scarer signal.

Conclusively, this limits the comparability between the estimated onsets for 20 and 28 kHz

because a TTS is expected to be greatest 0.5 octaves above the fatiguing stimulus (Kastelein et

al., 2014c; McFadden and Plattsmier, 1983; Popov et al., 2011).

In one case for each 20 and 28 kHz trials, we did not measure a TTS after the exposure, even if

the SEL exceeded the TTSonset (FIG. 9, unfilled circle, unfilled triangle). Although we took care

in counteracting any potential conditioning behaviour, the unaffected hearing threshold after

exposure could be a result of a self-protective mechanism, which actively dampens hearing

sensitivity, in expectation of an impending loud noise event. This self-mitigation has previously

been shown for four Odontocete species (Nachtigall et al., 2017). The harbour porpoise in this

study could have reduced its hearing abilities in order to prevent a TTS during exposure. Since

this effect seems to be of short duration (Finneran, 2018; Nachtigall et al., 2016), we could not

find a TTS when we measured the hearing in the period after the exposure, although expected

for these exposure levels, because either a TTS was not induced, or the self-mitigation was not

active anymore.

The study design was adjusted to counteract any conditioning behaviour by the porpoise, to

reduce hearing sensitivity in expectation of sound exposure. This was done by keeping all

experimental processes stable in exposure and non-exposure trials, besides sound exposure.

The measured hearing shifts are rather a result of a fatigued hearing after exposure, than a self-

mitigation. This phenomenon only occurred after conditioning the animals to expect an



63

unpleasant signal after a preceding warning stimulus (Nachtigall et al., 2017). In this study, we

tested hearing after exposure, so there was no expectation of an upcoming unpleasant event.

C. Estimated hazard zones

Based on the determined SPL-TTSonset of 155.2 dB re 1 µPa (p-p, TABLE IV), we estimated a

hazard zone, where a TTS could be induced in harbour porpoise hearing after the reception of

a single seal scarer signal. To estimate hazard zones, a theoretical sound propagation of seal

scarer signals was modelled. Specified by the manufacturer, the source level of the Lofitech

seal scarer is between 189 and 193 dB re 1 µPa (http://www.lofitech.co.uk/). To consider the

most precautionary approach, we assumed the highest reported source level of 193 dB re 1 µPa.

Based on this source level, a theoretical sound propagation was modelled as a simple

logarithmic regression. A similar approach with a simple logarithmic regression close to

spherical spreading proved to be valid for seal scarer sound propagation in the German North

Sea (Brandt et al., 2013b). The theoretical propagation was modelled for deep (spherical

spreading with a transmission loss of 20× log10 (r)) and shallow water (cylindrical spreading

with a transmission loss of 10× log10 (r)). A practical spreading with 15× log10 (r) in between

deep and shallow spreading was additionally modelled, resulting in three tested factors for the

slope of the transmission loss. The absorption coefficient α was estimated for typical North Sea

parameters (assuming 15°C water temperature, salinity of 35 ppt, a depth of 20 m, acidity of

pH=8) and a peak frequency of 14 kHz, at 1.5 dB km-1 (Ainslie and McColm, 1998).

Accordingly, for the received level we obtained 𝑅𝐿 = 𝑆𝐿 − 𝑠𝑙𝑜𝑝𝑒 × 𝑙𝑜𝑔10(r) − α × r.

Since the source level of 193 dB re 1 µPa corresponds to a rms value, the SPL-TTSonset (p-p)

was corrected. For the SPL-TTSonset of 155.2 dB re 1 µPa (p-p,) we obtain a rms SPL-TTSonset

of 146.2 dB re 1µPa (FIG. 10, horizontal dashed line), by subtracting 9 dB (Madsen, 2005).

Single seal scarer signals with a source level of 193 dB re 1 µPa are assumed to induce a TTS

in harbour porpoises up to distances between 211 m (spherical spreading in deep water) and

5.9 km (cylindrical spreading in shallow water), depending on theoretical sound propagation

(FIG. 10).

http://www.lofitech.co.uk/



64

FIG. 10: Estimated hazard area where single seal scarers signals exceed the determined SPL

TTSonset of 155.2 dB (pp), corresponding to a SPL TTSonset of 146.2 dB re 1 µPa (rms,

dashed line). The sound propagation of a seal scarer signal with a source level of

193 dB re 1 µPa (rms) was estimated by a simplistic logarithmic regression. The grey

shaded area represents the range between cylindrical (10×log10(distance)) and spherical

(20×log10(distance)) spreading. The solid line represents an assumed practical

(15×log10(distance)) sound propagation. The absorption coefficient was estimated at

1.526 dB km-1 for the main frequency component at of 14 kHz, a water temperature of

15°C, a salinity of 35 ppt, a depth of 20 m, acidity of pH=8 (Ainslie and McColm, 1998).

A temporary hearing impairment for harbour porpoises can be induced at distances up to

211 m or 5.9 km.

D. Cumulative effects of multiple exposure

The determined SEL TTSonset was determined for single exposures with 0.5 s long signals and

is assumed to be higher for multiple exposure, like it has been shown for the exposure with

single (Lucke et al., 2009) and multiple impulsive low frequency noise (Kastelein et al., 2015a,

2016). The equal energy hypothesis, meaning that the same amount of energy regardless of how

many events will always induce a TTS, is assumed to be inapplicable (reviewed in Southall et

al., 2007). An equal hearing shift can only be expected for continuous fatiguing noises or for

exposures with similar duty cycles (e.g. Finneran et al., 2010a, 2010b, Kastelein et al., 2015b,



65

2014; Mooney et al., 2009; Popov et al., 2014). In fact, the TTSonset decreases with increasing

SPL and duty cycle (Kastelein et al., 2015b, 2014b).

The inter pulse intervals of seal scarers are usually randomized at intervals between 0.6 and

90 s to counteract potential habituation effects (e.g. Lofitech used by Brandt et al. (2013)).

Within these varying inter pulse intervals the hearing can recover. Since higher duty cycles

induce a TTS at a lower SELcum, a TTS is more likely for multiple pulses with short inter pulse

intervals. However, further experiments are needed, to determine the TTSonset for varying sound

exposure levels and inter pulse intervals. This is critically needed to reliably predict a TTS

potential for fleeing harbour porpoises from multiple exposures.

E. Management approach

We could demonstrate that a single exposure to seal scarer signals can lead to hearing

impairment of non-target species at hundreds of meters. Negative effects could be even more

dramatic, if multiple ADDs are applied simultaneously on multiple cages within a single

aquaculture or at further adjacent sites. We obtained a frequency weighted TTSonset of

138 dB re 1 µPa²s, which is surprisingly 15 dB lower than the updated recommended marine

mammal noise exposure criteria for continuous noise (Southall et al., 2019). Following these

recommendations, a PTSonset is estimated 20 dB above the TTSonset level, which corresponds to

158 dB re 1 µPa²s, according to our results. Regarding the high source level of commercially

available seal scarers, even a PTS can be induced at very close distances. Given the evidence

that seal scarers can induce an injury in harbour porpoises, no matter if defined as TTS (e.g.

German regulation, BMU, 2014) or PTS (most other states in Europe and in the United States,

e.g. (Southall et al., 2019)), there is a clear requirement to manage the application of seal

scarers.

For the application of seal scarers to deter seals around aquacultures, a shift to lower frequencies

could decrease the risk for hearing impairment for the harbour porpoise as a non-target species.

A shift to lower frequencies, as also proposed by Götz and Janik (2013), would be beneficial,

since the hearing abilities for lower frequencies are better for seals than for porpoises (Kastelein

et al., 2002; Ruser et al., 2016a). Deterring signals for seals, should not contain much energy

above 5 kHz, if Odontocetes use habitats around the fish farm (Götz and Janik, 2013). On the

contrary, using lower frequencies could be worse for baleen whales. Therefore it has to be

considered, if baleen whales inhabit areas around the site, where ADDs are applied. In case of



66

further developments of acoustic deterrent devices, the target specificity must be validated by

independent studies prior deployment around aquacultures.

Although ADDs are a significant and chronic source of underwater noise pollution along the

Scottish west coast around aquacultures with a steady increase in ADD usage and substantial

geographic expansion (Findlay et al., 2018), neither licence is required to deploy these devices,

nor any statistics on usage exist (Coram et al., 2014). An unwanted deterrence of harbour

porpoises has been regarded as a comparatively benign side effect, while ADDs were deployed

to counteract economic loss by seals. While behavioural responses and exclusion from key

habitats of harbour porpoises were evaluated as insufficient arguments to regulate the use of

ADDs, the evidence that a TTS or even PTS can be induced, must lead to a regulation system.

Additionally, an adjustment of the source level of ADDs has to be considered, to reduce the

potential impact on harbour porpoise hearing. This adjustment should be taken into account for

the use around aquacultures, but also as a deterrent device for harbour porpoises, prior to pile

driving activities. From a conservation point of view, this deterrence should be adjusted to the

expected TTS hazard zone from pile driving strikes. While received levels above the presented

TTSonset are assumed to induce increased hearing thresholds, the deterrence efficiency would

be decreased accordingly, which is a problem from a commercial perspective (Götz and Janik,

2013). We therefore advice to down regulate source levels as a protective measure and use an

amplitude ramp up, giving harbour porpoises sufficient time to leave hazardous areas.

F. Conclusion

Seal scarer signals have the potential to impair harbour porpoise hearing. The TTSonset was

determined at an SEL of 141.8 dB re 1 μPa²s at the hearing threshold of 20 kHz and at a 146.9

dB re 1 μPa²s for 28 kHz hearing frequency. The frequency weighted TTSonset was 15 dB below

the recommended Marine Mammal Noise Exposure Criteria (Southall et al., 2019). Hazard

zones, where a TTS can be induced by a single exposure are dependent on sound propagation,

but are expected to be between 211 m and 5.9 km for reported source levels of up to 193 dB re

1 µPa. Based on our findings, effects of multiple exposure cannot be predicted due to the

random inter pulse intervals. In order to use seal scarers to deter harbour porpoises instead of

impairing its hearing, we suggest to down regulate source levels to the desired deterrence range

and to slowly increase the source level, giving harbour porpoises time to flee.



67

V. Acknowledgement

Experiments within this study were conducted within the project “Impact of underwater noise

on marine mammals (UWE)” FKZ 3515 82 2000), funded by the Federal Agency for Nature

Conservation (BfN). We would like to express our gratitude to the team of animal trainers of

the Fjord & Bælt Centre, especially to Fredrik Johansson, for the huge effort in training and

handling the harbour porpoises prior to and during experiments.



68

VI. Appendix

A: Measured hearing thresholds for baseline hearing measurements

TABLE V shows the results for the hearing tests which were conducted without any prior

exposure. The measured hearing thresholds were used to determine the baseline hearing

threshold.

TABLE V: Measured hearing thresholds, which have been used to calculate mean hearing

thresholds

Date Frequency

in kHz

Hearing threshold

in dB re 1 µPa

13.07.2017 20 87.6

13.07.2017 20 93.0

04.09.2017 20 85.8

04.09.2017 20 86.2

22.09.2017 20 86.5

27.06.2018 20 91.8

28.06.2018 20 82.1

28.06.2018 20 86.5

06.07.2018 20 95.7

06.07.2018 20 88.2

06.07.2018 20 92.0

17.07.2018 20 87.2

19.07.2018 20 89.6

20.07.2018 20 96.4

22.08.2018 20 93.6

23.08.2018 20 92.6

04.09.2018 20 92.6

13.09.2018 20 92.2

18.09.2018 20 87.9

19.09.2018 20 93.0

29.06.2017 28 84.0

10.10.2018 28 87.2

10.10.2018 28 84.7

10.10.2018 28 89.9

11.10.2018 28 89.0

17.10.2018 28 82.4

17.10.2018 28 83.7

18.10.2018 28 86.1

18.10.2018 28 87.3

25.10.2018 28 80.0



69

Appendix B: Measured hearing thresholds after exposure

TABLE VI shows the measured hearing thresholds after the exposure to the artificial seal scarer

signal

TABLE VI. Measured hearing thresholds after exposure, which resulted in a significant hearing

shift, relative to the baseline. Asterisks indicate levels of significance (*: p<0.05; **:

p<0.01; ***: p<0.001).

Date Frequency

kHz

Threshold

dB re 1 µPa

Exposure

dB re 1 µPa²s

z-value p-value

17.07.2018 20 93.73 138.4 1.01 0.1570

19.07.2018 20 89.75 137.6 -0.08 0.5300

20.07.2018 20 100.7 148.4 2.90 0.0019**

22.08.2018 20 89.2 147.2 -0.22 0.5889

31.08.2018 20 108 157.5 4.89 0.0000***

04.09.2018 20 103.7 154.2 3.72 0.0001***

13.09.2018 20 102.2 155.7 3.31 0.0005***

18.09.2018 20 93.3 143.1 0.89 0.1867

19.09.2018 20 98.3 145.3 2.25 0.0122*

11.10.2018 28 91 146.9 1.92 0.0273*

17.10.2018 28 92.6 153.1 2.47 0.0067**

18.10.2018 28 101 155.6 5.37 0.0000***

24.10.2018 28 96.7 152.5 3.89 0.0001***

25.10.2018 28 79.7 148.4 -1.98 0.9760



70

Appendix C: Relationship between SEL and SPL of exposures

FIG. 11 shows the modeled correlation between sound exposure and sound pressure levels of

the recorded artificial seal scarer sounds. This linear regression allowed for the transfer of the

determined SEL-TTSonset to the SPL-TTSonset.

FIG. 11. Linear regression of SEL–SPL of all played back seal scarer signals during hearing

tests at 20 and 28 kHz. Black points represent the unweighted SEL of all exposures. The

circles represent the NOAAHF frequency weighted SEL of all exposures. The regression

was used to estimate the corresponding SPL-TTSonset from the SEL-TTSonset.



71

Appendix D: Auditory frequency based weighting of exposures and resulting weighted

TTS onset

FIG. 12 shows the auditory based frequency weighted (NOAAHF) sound exposure levels of the

fatiguing stimuli and the measured hearing thresholds after exposure. Based on these results, a

frequency weighted TTSonset was determined with a linear regression.

FIG. 12: Effects of seal scarer exposure on hearing thresholds at 20 (circles) and 28 kHz

(triangles). The TTSonset was determined with a linear regression for 20 kHz at 138.4 and

for 28 kHz at 143.9 dB re 1 µPa2s.

Ultrasonic aqua flowmeters in rivers affect harbour porpoise hearing

72

Manuscript:

T. Schaffeld, J.G. Schnitzler, B.J. Baltzer, M. Fischer, M. Schuster, A. Ruser, U. Siebert (2020).

Ultrasonic aqua flowmeters in rivers affect harbour porpoise hearing

Chapter 3: Ultrasonic aqua flowmeters in rivers affect harbour porpoise hearing

73

Chapter 3: Ultrasonic aqua flowmeters in rivers affect harbour porpoise

hearing

T. Schaffelda, J.G. Schnitzlera, J. Baltzera, M. Fischerb, M. Schusterb, A. Rusera, U. Sieberta

a Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine


b DW-ShipConsult GmbH, Lise-Meitner-Straße 9, 24223 Schwentinental, Germany

Abstract

After decades of absence, reports of harbour porpoise sightings in the Elbe or Weser River

increased again over the last years. Harbour porpoises annually occur, with a peak in spring in

the port of Hamburg, despite the high number of present vessels. This seasonal occurrence

might be related to anadromous prey species, which could represent an important food source

when travelling upstream for spawning. After numerous strandings of dead animals in 2016

close to the port of Hamburg, an acoustic flowmeter in the port was suspected as a cause. By

an initiative of the Hamburg Port Authority, which operates the flowmeter, underwater noise

was recorded in this area. The flowmeter emits short pulses with a length of 0.2 s and a

frequency of 28 kHz, which can be heard by harbour porpoises. These signals are transmitted

from the northern and southern banks of the Elbe River, which are about 400 m away from each

other. The transmission alternates every 2 s between the two sides , with a pulse rate of 4.1 s

for each of the flowmeters. Within this chapter, we evaluated the potential of these signals to

induce a temporary threshold shift (TTS) in harbour porpoises by a single or multiple exposure.

The modelled sound field demonstrates, that the acoustic flowmeters emit pulses in a highly

directional beam. The pulses contain sufficient energy to induce a TTS in harbour porpoises by

the exposure of single signals up to a distance of approximately 72 m from the sound source.

Although the area with pulses of highest amplitude are comparably small, total received sound

exposure levels of up to 165 dB re 1 µPa²s were estimated for travelling harbour porpoises The

total received cumulative energy for harbour porpoises travelling along the flowmeters are

mainly dependent on the timing and position of the animals. Accordingly, a close approach to

the flowmeter at the time of transmission should be prevented. This could be the case, if vessels

force harbour porpoises to elude closer to the flowmeters. Following the recommendations of

this chapter, the HPA adjusted the source level of the flowmeter.


74


A.R., M.S. and U.S. were involved in designing the project and applying for the project grant.

A.R. and T.S. prepared the underwater noise measurements, which were conducted by A.R.,

T.S. and M.S. The underwater noise recordings were analysed by M.F. and M.S. who provided

the results as a modelled sound field to T.S.. Hearing tests with a harbour porpoise in human

care were performed by A.R.. All analyses to evaluate the TTS potential for a harbour porpoise

in the sound field of the acoustic flowmeters were performed by T.S. under supervision of A.R.,

J.S. and U.S. All authors provided critical feedback and helped to shape the research and

analysis. The manuscript was written by T.S. with supportive contributions to the final version

of A.R., J.S., J.B. and U.S..


75

I. Introduction

Harbour porpoises (Phocoena phocoena) inhabit coastal waters of the northern hemisphere

(Gilles et al., 2016; Hammond et al., 2017). It is the only cetacean representative, with a regular

reproduction in German waters (Gilles et al., 2016). Historic reports prove that harbour

porpoises commonly inhabited lower stretches of large rivers in the 19th century as shown by

sightings or strandings in the Weser River south of Bremen (Häpke, 1880) or even up to

Magdeburg, which is upstream the Elbe River at a distance of 400 km from the coast (Kölmel,

1998). Following decades of absence, harbour porpoise sightings increased again in rivers

entering the German North Sea (Wenger et al., 2016). In 2013, a reporting system was

established, allowing collecting harbour porpoise sightings (Wenger et al., 2016). This resulted

in 233 reports of harbour porpoises in the lower Elbe River between 27th of February and 9th of

July in 2013. A large extent of the sightings were reported close to the port of Hamburg. In

addition to the reporting system, a static acoustic monitoring with porpoise click detectors (C-

POD, Chelonia Limited, UK) was conducted, which could confirm a clear seasonality in

detections with a peak in spring (Wenger et al., 2016). The acoustic monitoring revealed the

continuous presence of harbour porpoises in the port of Hamburg over the entire monitoring

period from February to June, reaching a maximum of 90 % detections per daytime in the

middle of April. According to newspaper reports, 80-100 harbour porpoises were

simultaneously present in this area, occurring in groups of up to 10 animals, which were seen

foraging together (https://www.abendblatt.de/hamburg/article207486167/Schon-100-Wale-

im-Hafen-Gefahr-durch-Hafengeburtstag.html, 26.04.2016 and pers. comm. Denise Wenger).

In the lack of an established systematic monitoring of harbour porpoises, these counts have to

be considered with great caution, since these are not corrected for repeated sightings. Due to

the determined strong seasonality in harbour porpoise presence and the determined foraging

activity by sightings and acoustic monitoring, it is assumed that harbour porpoises enter large

rivers because they follow migrating anadromous fish species (Wenger et al., 2016). Spatial

and temporal occurrence of harbour porpoises in this area correlates with the annual migration

of anadromous fish species like smelt (Osmerus eperlanus) and twaite shad (Allosa fallax),

which are known to spawn in this area (Thiel, 2015).

In 2013, 26 dead harbour porpoises were found around the area of the harbour in Hamburg

(Wenger et al., 2016). Since no necropsies were conducted, no cause of death could be


76

determined. Harbour porpoises critically rely on a well-functioning hearing system. Harbour

porpoises produce short high frequency clicks to acoustically sense their environment by the

reception of returning echoes (e.g. Verfuß et al., 2005). This ability to echolocate is shared with

bats (reviewed in Fenton et al., 2014) and enables navigation (Verfuß et al., 2005) as same as

finding and catching prey (DeRuiter et al., 2009; Verfuß et al., 2009) in complete darkness.

Among the toothed whales, which are generally vulnerable to noise disturbance, harbour

porpoises are considered to be very sensitive to effects of noise and are therefore regarded as

an indicator species in noise impact evaluations (Southall et al., 2019; Tougaard et al., 2015).

In European waters, harbour porpoises are protected amongst others within the framework of

the Habitats Directive (listed in annexes II and IV European Union, 1992) and Council

Regulation 812/2004 (European Union, 2004). This protective regulation implies that special

areas should be established for their conservation with deliberate actions of killing, disturbing,

injuring and habitat deterioration being prohibited throughout its area of distribution (Council

Directive 92 / 43 / EEC, Article 12.1). Sources of anthropogenic disturbance are numerous for

harbour porpoises in German waters. The largest impact is caused by unintended bycatch in

set-net fisheries (Korpinen and Braeger, 2013; Wehrmeister et al., 2013), chemical pollution

(Huber et al., 2012; Mahfouz et al., 2014) and the introduction of underwater noise (Akkaya

Bas et al., 2017; Brandt et al., 2018; Dyndo et al., 2015; Sarnocińska et al., 2020; Wisniewska

et al., 2018b). The exposure to underwater noise can induce a temporary threshold shift (TTS)

in harbour porpoise hearing (Kastelein et al., 2016; Lucke et al., 2009). Since a hearing shift is

regarded as an injury in Germany, noise regulation aims at preventing a TTS. Accordingly, the

evidence of a TTS potential from impulsive noise (Lucke et al., 2009) was adopted very quickly

in noise regulation measures during the construction of Offshore Wind farms in Germany

(BMU, 2014).

Since strandings of cetaceans have been associated with anthropogenic sonar signals in the past

(reviewed in Simmonds et al., 2014) and the high sensitivity of harbour porpoises towards noise

are commonly known (Southall et al., 2019), an acoustic device in the port of Hamburg was

suspected as the cause for the reported strandings. This device is applied by the Hamburg Port

Authority (HPA) in the Elbe River in the area of Finkenwerder in order to measure the water

flow velocity. The flow speed is obtained from the measured travel time of ultrasonic acoustic

signals, which are transmitted from both sides of the river. To evaluate the potential of this


77

flowmeter, the HPA funded a project themselves, including underwater noise measurements

and a biological evaluation, because they wanted to exclude, that the flowmeter has negative

impacts on harbour porpoises. The overarching goal of chapter 3 is an estimate of the TTS

potential for harbour porpoises from this underwater flowmeter. This was achieved by

underwater noise measurements in the port of Hamburg and the application of data from

previous hearing tests with a harbour porpoise in human care.

A. Study area and underwater noise measurements

The flowmeter of the HPA is located in Hamburg Finkenwerder, which is in the West of

Hamburg in close proximity to the Airbus airport and adjacent to the Natura 2000 conservation

area “Neßsand”. This system consists of two measuring devices, which are located at the north

and south riverbank. The water depth at this site is almost constant 18 m with a very steep slope

in the area close to the riverbanks.

The ultrasonic aqua flowmeter transmits acoustic signals from both sides of the Elbe River to

obtain the flow speed from the measured travel time. The underwater noise recordings were

conducted on two consecutive days (1st and 2nd of June in 2017) on board of the “Reinhard

Woltman” (GER) of the Hamburg Port Authority (HPA). Recordings were made at three depth

levels (2, 5, 8 m). This linear vertical hydrophone array was attached to a rope, which was fixed

with snap hooks to a steel guidance cable. The steel cable was weighted by a 500 kg concrete

anchor and lowered by a winch. At each water depth, underwater noise was recorded by two

hydrophones with different sensitivities, to cover a wide dynamic range (see Fischer and

Schuster 2017 for more details). Underwater noise was recorded using the Avisoft Sound

Recording Software (Avisoft Bioacoustics, Germany). Signals were pre-amplified with an

eight-channel power amplifier (B2008APC – SN1212000, ETEC, DK) with a passband from 1

to 300 kHz. Recordings were digitized with a data acquisition card (NI USB 6251, National

Instruments, USA) sampling at 750 ksamples s-1 and saved as wav files with a 24-bit resolution.

Acoustic signals from the flowmeter on both sides of the Elbe River were recorded on transects

along the river. Therefore the vessel was steered upstream the flowmeter, where the engine was

stopped. The vessel drifted on transects at different distances to the flowmeters downstream,

while the hydrophone array was in the water. Additionally, underwater noise was recorded

during one transect from one flowmeter to the other by diagonally crossing the Elbe River.


78

During this transect the engine was running. A mobile GPS device (Garmin 72H, CH) on top

of the hydrophone array recorded simultaneously GPS positions at a sample rate of 1 Hz.

The underwater noise recordings, which were gathered on the different transects were analysed

with custom written manuscripts in MATLAB (MathWorks, USA) by DW-ShipConsult (see

Fischer and Schuster 2017 for more details). The sound pressure level (SPL, peak-to-peak) and

sound energy level (SEL) were calculated for each detected signal and assigned to the

corresponding GPS position on the track. The positions of the flowmeters in the North and

South of the Elbe River, the recorded GPS track of the vessel and the positions, where an

acoustic signal could be recorded are shown in (FIG. 13). The sound pressure levels (SPL peak-

to-peak in dB re 1 µPa) are given by colour coded points on the tracks.

FIG. 13: Study area in the Elbe River in the West of Hamburg. The positions of the underwater

flowmeters are shown by red triangles. The GPS tracks of the vessel are presented as lines,

which are separated by colour for different days. The positions where signals of the

flowmeter could be detected in the acoustic recordings are given by points, which show

the determined sound pressure level by a colour coding.


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B. Sound propagation model

A sound propagation model was run by DW-ShipConsult based on the determined sound

exposure levels for single acoustic signals and the corresponding locations. The aim of the

sound propagation model was to generate a high-resolution array with modelled SELs of single

signals for the entire area of investigation. The sound transmission of the flowmeter signals is

dependent on the propagation loss but also on the directivity of the sound source. Therefore,

the propagation loss was estimated based on the recordings from the transect between the two

flowmeters only, as this was assumed to be in the center of the beam. The source level was

estimated from these results by the use of a logarithmic regression. The further determined

signals were used to determine the directional characteristic of the transmission beam. As a

result, the source level was determined at a sound pressure level of 210 dB re 1 µPa for both

flowmeters at the north and south river bank. The signal consisted of a 0.2 s tone at a frequency

of 28 kHz with a pulse rate of 4.2 s. The emission of signals alternates between the north and

south flowmeter, leading to an effective pulse rate of 2 s.

The sound propagation was modelled for a three-dimensional area reaching 1000 m (x-axis)

down- and upstream the acoustic flowmeter, a width of 391 m between the two flowmeters (y-

axis) and a depth of 18 m (z-axis). The received level was calculated for each cube within the

three-dimensional array with a resolution of 1×1×0.1 m (x×y×z). This calculation was based on

a simplified ray tracing model and the passive sonar equation. Broadly speaking, the model

assumes a spherical propagation loss of 20×log10(distance) and considers a three-way-

propagation, taking the direct path and the first reflection from the surface and the bottom into

account. This propagation model is described in more detail in Fischer and Schuster (2017).

The estimated source level, propagation loss over distance and the directivity index were taken

into account. The estimated energy for each cube within the array corresponds to the sum of the

direct path and the first reflection from the surface and the bottom. Absorption was not

considered, as this was assumed negligible in freshwater and for short distances.

The results of the sound propagation modelling were delivered as MATLAB files, containing

single sound exposure levels in a three-dimensional array. These files were loaded in R, using

the function read.mat() of the “rmatio” package (Widgren and Hulbert, 2019). The sound field

was visualized as a 2D plot in R (R Core Team, 2019). A top view on the acoustic field for two


80

exemplary water depths (5 and 12 m) is shown in FIG. 14 each for the flowmeter in the north

and south.

FIG. 14: Top view on the modelled sound field of the acoustic flowmeter on the north (top row)

and south (bottom row) riverbank. The sound field is shown for a depth of 5 m (A, B) and

12 m (C, D). The sound exposure level of a single pulse is shown by colour coding in

dB re 1 µPa²s.


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The single arrays of modelled sound fields for the two flowmeters were combined in a shared

array (FIG. 15). This was done by transferring the arrays to the linear scale, summing up the

values of both arrays and re-transferring the values to the logarithmic scale. This combined

array was used in all further simulations.

FIG. 15: Top view on the combined sound field of the two flowmeters at a depth of 5 m. This

combination derives from summing up the single arrays for the two flow meters. The

flowmeters alternately emit pulses with a pulse rate of 2 s. The pulse rate for each

flowmeter is 4.1 s. The colour coded sound exposure level represents a double pulse,

meaning a pulse of each flowmeter.

C. Effect of 28 kHz fatiguing sound on harbour porpoise hearing

The hearing tests with the harbour porpoise in human care were conducted at the Fjord & Bælt

Centre in Kerteminde (DK). Hearing thresholds were derived from measurements of auditory

evoked potentials (AEP) in the same manner as described in chapter 2. The database derives

from measurements of auditory evoked potentials in 2014, which remain unpublished to data.


82

The hearing tests were conducted in the project „Cluster 7“ funded by the Federal Agency for

Nature Conservation (FKZ 3514824000). The animal was exposed to a fatiguing stimulus using

the same procedure as described in chapter 2. The fatiguing stimulus was a tone at 28 kHz with

a duration of 3.5 s. The harbour porpoise was exposed once a day with varying sound exposure

levels. Following the same procedure as described in chapter 2, the SEL-TTSonset was defined

as a significant shift from baseline hearing. This TTSonset was estimated by a linear regression

of sound exposure levels (dB re 1 µPa²s) on the delta in the determined hearing threshold (in

dB), compared to the baseline.

D. Simulation of harbour porpoise migration through acoustic field

In order to evaluate the effect of this acoustic underwater flowmeter on the hearing of harbour

porpoises, we simulated swimming tracks through the area. We defined transects in the

direction of the river with a constant y-axis position, passing the flowmeters. We simulated

such transects for each of the 391 m possible y-axis positions over the complete width of the

river. For each of these 391 simulated tracks along the x-axis, we calculated harbour porpoise

positions at the time of the reception of the acoustic flowmeter signals. We calculated the

positions of the harbour porpoise on each track from 1000 m before up to the distance of 1000 m

behind the flowmeters. The first reception was assumed at the starting position at a distance of

1000 m to the flowmeter. Each following reception was obtained from the pulse rate×swim

speed. We used three literature based swim speed levels, which should represent a maximum,

mean and slow swim speed scenario. This broad range was chosen to represent harbour

porpoises at all life stages and to regard also slowly swimming individuals, like mother and calf

pairs. Data on the swim speed of harbour porpoises are rare due to their inconspicuous lifestyle

and poor accessibility. Only a few studies focused on the analysis of swim speed of harbour

porpoises. Maximum swim speed for animals in human care were determined at 4.3 m s-1 (Otani

et al., 2001) and in the wild at 4.3 and 6.1 m s-1 (Gaskin et al., 1974; Otani et al., 2000). A mean

swim speed of a free-ranging harbour porpoise was determined at 0.9 m s-1 (Otani et al., 2000).

Since the authors are not aware of any publication of swim speed levels of harbour porpoises

in river systems, the effect of flow velocity on swim speed was estimated as the sum of the

maximum swim speed and assumed maximum flow velocity. The maximum flow velocity was

estimated at 1.6 m s-1 (pers. comm. Nino Ohle in 2017, HPA). Accordingly, harbour porpoise

flights were simulated at swim speed levels of 0.9, 4.3, 6.1 and 7.7 m s-1. Simulated harbour


83

porpoise positions on flight tracks with the four tested swim speeds are shown exemplary in

TABLE VII for the reception of the first five pulses on the flight track.

TABLE VII: Harbour porpoise positions on simulated flight tracks. Four different swim speed

levels were used to determine the positions, where a harbour porpoise would be on the

track each 4.2 s, which corresponds to the pulse rate of the flowmeter. The received sound

exposure level for each of these positions was obtained from the modelled acoustic array.

All received SELs were accumulated for a complete transect.

Pulse Time Position on x-axis (in m) at speed level of

# in s 7.7 m s-1 6.1 m s-1 4.3 m s-1 0.9 m s-1

1 0 0.0 0.0 0.0 0.0

2 4.2 32.3 25.6 18.1 3.8

3 8.4 64.7 51.2 36.1 7.6

4 12.6 97.0 76.9 54.2 11.3

5 16.8 129.4 102.5 72.2 15.1

Because the acoustic flowmeter emit signals in a very narrow beam (FIG. 15), the received

levels can show large variations close to the flowmeters. This may result in uncertainties when

estimating the cumulative received levels, since these are dependent on the timing when the

harbour porpoise enters the main beam with regards to the pulse rate. We addressed this time

related variability by shifting the start positions. For instance, a harbour porpoise swimming

with a speed of 6.1 m s-1 travels around 26 m between two pulses with a pulse rate of 4.1 s.

Therefore, we tested multiple starting positions corresponding to the meters a harbour porpoise

can travel for the tested swim speed within one pulse interval for each track. The received level

for each position on the track was obtained from the modelled acoustic array. Since we do not

know at which water depth a harbour porpoise would most likely migrate through the area

around the acoustic flowmeters, we assumed a continuous diving depth of 5 m for practical

reasons. However, the sound field does not show substantial differences in received sound

exposure levels over depth. The estimated received levels from both acoustic flowmeters were

accumulated for each simulated track.

E. Evaluation of potential to induce a TTS

The potential to induce a TTS for harbour porpoises by the exposure to signals of the flowmeter

was evaluated by the use of the modelled acoustic field and simulated harbour porpoise

presence and travelling. A TTS can be induced in three different scenarios. First, single pulses

can contain sufficient energy to induce a TTS. For this scenario, we used the SEL-TTSonset,


84

which derives from the hearing tests with a harbour porpoise in human care exposed to a 28 kHz

tone. A TTS can be induced also by multiple exposures. The single SEL-TTSonset cannot be

directly transferred to a multiple exposure, as the same energy of exposure does not

automatically induce the same shift, if the energy is received over a longer duration (as

discussed in chapter 2). The assumption that equal cumulative energy induces an equal hearing

shift is only valid for continuous fatiguing noises or for exposures with similar duty cycles (e.g.

Finneran et al., 2010a, 2010b, Kastelein et al., 2015b, 2014; Mooney et al., 2009; Popov et al.,

2014). We followed instead the suggested noise exposure criteria of Southall et al. (2019, table

6), who suggested a frequency weighted cumulative SEL-TTSonset of 153 dB re 1 µPa²s. Since

this SEL-TTSonset is frequency weighted, based on the audiogram of harbour porpoises

(National Oceanic and Atmospheric Administration; National Marine Fisheries Service, 2016;

Southall et al., 2019), this onset cannot be transferred directly to the single pulse exposure levels

of the modelled sound field. According to the proposed frequency weighting, the amplitude of

a 28 kHz signal decreases by 0.3 dB. This means, that the SEL-TTSonset for multiple pulses

accounts for 153.3 dB re 1 µPa²s. Flight transects were simulated in order to estimate the TTS

potential for a multiple exposure. For this case, we tested, if the cumulative received SEL for

the entire track exceeds the cumulative SEL-TTSonset suggested by Southall et al. (2019). As a

third approach, we evaluated the potential to induce a TTS for harbour porpoises, which do not

show a flight response and rather stay in the area. Based on the sound field of the flowmeter

and the determined pulse rate, we calculated the time for each position, needed to exceed the

cumulative SEL-TTSonset of 153 dB re 1 µPa²s (frequency weighted).


85

II. Results

A. Baseline hearing thresholds

Baseline hearing at 28 kHz was measured in 14 trials resulting in a mean hearing threshold of

82.0 dB re 1 µPa ± 2.4 dB (range 78.2-88.1 dB re 1 µPa). We followed the same approach to

define a significant TTS as described for the measurements in chapter 2. With regards to the

determined hearing threshold and the standard deviation, we obtained a critical value (p≤0.05)

of 85.7 dB re 1 µPa as the threshold for a significant hearing elevation. Accordingly, any

hearing shift larger than 3.8 dB was regarded as a TTS.

B. Post-exposure thresholds

Hearing thresholds after an exposure to the 28 kHz fatiguing tone were conducted in eleven

trials. The animal was exposed to SELs between 139.7 and 156.3 dB re 1 µPa²s. Post-exposure

hearing thresholds were measured between 86.7 and 97.6 dB re 1 µPa, accounting for elevated

thresholds between 4.8 and 15.7 dB. Accordingly, all measures post-exposure thresholds

exceeded the critical value of 3.8 dB. The TTSonset was estimated by a linear regression of

threshold shifts on sound exposure levels. According to the linear regression (intercept=-83.95,

slope=0.64), the critical value of 3.8 dB was exceeded at an SEL of 137.4 dB re 1 µPa²s (FIG.

16). Conclusively, this SEL corresponds to the TTSonset for a single exposure to a 28 kHz tone.

C. TTS potential of flowmeter for single pulses

The SEL-TTSonset for a single exposure was determined at 137.4 dB re 1 µPa²s. The underwater

noise measurements and the following sound propagation model could reveal that the source

level of the underwater flowmeter exceeds this TTSonset. This means, that single pulses contain

sufficient energy to induce a TTS in a harbour porpoise. The flowmeters are highly directional

leading to a narrow beam, in which amplitudes are highest. Within the beam of highest

amplitude, the modelled sound fields at a depth of 5 m show single SELs above the TTSonset up

to a distance of approximately 72 m from the flowmeter in the north and 74 m from the

flowmeter in the south. Since the flowmeters are not aligned in a 90° angle to the x-axis these

distances in the beam do not correspond to the distance in the y-axis, meaning the position in

the width of the river. Harbour porpoises which travel along a transect need to keep a distance

of 40 m to the flowmeter in the north and 60 m to the flowmeter in the south in order to avoid

a TTS from a single exposure.


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FIG. 16: Effects of 28 kHz tone exposure on hearing thresholds at 28 kHz (black circles). The

horizontal red dashed line represents the critical value of 3.8 dB shift, which indicates the

threshold of significance. A linear regression was calculated in order to estimate the

TTSonset, using only exposures, which led to a TTS. The TTSonset at 28 kHz was determined

at 137.4 dB re 1 µPa²s.


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D. Received levels on simulated flights

The received energy for harbour porpoises travelling along the acoustic flow meters were

simulated, assuming swim speed levels between 0.9 and 7.7 m s-1. We accumulated the received

cumulative sound exposure levels for each complete transect line. The results of this simulation

are presented in FIG. 17. The position of the simulated transect line within the width of the river

is shown on the x-axis in m. The received cumulative SEL in dB re 1 µPa²s for the complete

transect line is shown on the y-axis. The received cumulative SEL is given by a black line,

assuming the reception of the first pulse at a distance of -1000m. The grey area indicates the

possible received minimum and maximum received levels. This deviation arises from the pulse

rate and narrow beam of the flowmeter. We tried to address this problem by varying the position

of the first received pulse. The number of variations is dependent on the swim speed and the

pulse rate. For the swim speed of 7.7 m s-1 33 positions of the first reception were simulated

(7.7m s-1×4.2s=32.3 m). The numbers of possible starting positon are given in the top right

corner. This simulation approach indicates, that travelling harbour porpoises with swim speed

levels of 7.7, 6.1 and 4.3 m s-1 would not receive sufficient energy from multiple pulses to

expect a TTS, according to the SEL-TTSonset of 153.3 dB re 1 µPa²s. The TTS-potential is

comparably low. However, harbour porpoises swimming with a speed of 0.9 m s-1 could receive

cumulative sound exposure levels exceeding the SEL-TTSonset up to distances of about 20 m.

The received SELcum is strongly dependent on the timing of pulses. If the harbour porpoises is

within the narrow beam of highest amplitude at the moment, when a pulse is emitted, the

received cumulative SEL can be as high as 165 dB re 1 µPa²s for all swim speed levels and a

TTS must be assumed.


88

FIG. 17: Received cumulative sound exposure levels (SELcum) on simulated transects along

acoustic flowmeters.The simulation was performed assuming four different swim speed

levels (0.9-7.7 m s-1) and a continuous depth of 4.7 m. The received SELcum (black line)

represents the cumulative SEL a harbour porpoise would receive, when travelling along

a constant position within the width of the river (y-axis). The red horizontal line represents

the cumulative SEL-TTSonset of 153.3 dB re 1 µPa²s, estimated by (Southall et al., 2019).

The variability in the received SELcum, which derives from the time of entering the beam

of highest amplitude, is shown by a blue area, which represents the minimum and

maximum values. The number of simulated starting positions for the reception of the first

pulse is shown in the top-right corner.


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E. TTS potential for harbour porpoise which stay around the flowmeters

In order to estimate the potential to induce a TTS in harbour porpoises, which do not show a

flight response and rather stay within the area, we calculated the needed time to exceed the

cumulative SEL-TTSonset. This was done for each position within the modelled sound field and

the pulse rate of 4.1 s. FIG. 18 displays a top-view on the sound field at a depth of 5 m. The

needed time to exceed the cumulative SEL-TTSonset in minutes is presented by colour coding.

Only the area where a TTS can be induced by multiple pulses within 60 minutes is marked. The

area of highest potential to induce a TTS is between the two flowmeters. If the harbour porpoise

stays within this area a TTS can be induced within 1 and 30 minutes. The risk for a TTS strongly

decreases, when leaving the narrow beam of highest amplitude.

FIG. 18: Required time within sound field to exceed cumulative SEL-TTSonset.The time in

minutes is presented (colour coded), which is needed to exceed the cumulative SEL-

TTSonset of 153.3 dB re 1 µPa²s. Only the areas, where a TTS can be induced within

60 minutes for a pulse rate of 4.1 s are marked. The flowmeter positions are marked by

black triangles.


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III. Discussion

The distribution of harbour porpoises largely overlaps with areas where anthropogenic activities

take place. A perfect management of these activities would prevent any negative impact on

harbour porpoise health or behaviour but simultaneously maintain anthropogenic activities. The

results of chapter 3 could show that the acoustic flowmeter has the potential to induce a

temporary threshold shift in harbour porpoises by the exposure to single, but also to multiple

signals.

A. Evaluation of potential effects of the flowmeter on harbour porpoise

hearing

The hearing tests with a harbour porpoise in human care could show, that a 28 kHz signal with

a length of 3.5 s can induce a TTS, if sound exposure levels exceed 137.4 dB re 1 µPa²s.

Transferred to the modelled sound field of the acoustic flowmeters in the Elbe River, a TTS can

be induced by the exposure to single signals at close distances up to 74 m. Since harbour

porpoises have good hearing abilities at 28 kHz (e.g. Ruser et al., 2016a) it is very likely, that

signals can be heard from larger distances and animals might not come so close to the

flowmeter. The simulation of harbour porpoises travelling along the acoustic flow meter could

reveal a high variability in the received cumulative SEL. This large variability is due to the

pulse rate of 4.1 s and the narrow beam of the flowmeter. Although harbour porpoises

swimming at lower speed levels would receive more pulses on the complete track, the highest

possible received levels, due to the timing variability, do not differ significantly between

different swim speed levels. This clearly demonstrates that the timing and the position of signal

reception are the most important factors for the received cumulative SEL. The simulation could

show, that received cumulative SELs of up to 165 dB re 1 µPa²s are possible for travelling

transect at close distances (FIG. 17). Following the recommend noise exposure criteria for

marine mammals (Southall et al., 2019), a permanent threshold shift is expected at a cumulative

SEL of 173 dB re 1 µPa²s. The highest SEL within the acoustic field was estimated at a SEL of

165 dB re 1 µPa²s. To exceed the PTS-SELonset of 173 dB re 1 µPa²s, seven pulses with a SEL

of 165 dB 1 µPa²s would be needed. Accordingly, a harbour porpoise would need to stay at

close distance to the flowmeter for 7×4.1 s=28.7 s. Due to this relatively long time, a harbour

porpoise must stay at close distance to the flowmeter, it is very unlikely, that a PTS will be

induced for this assumed TTSonset. The presence of harbour porpoises in the port of Hamburg is


91

believed to be driven by the migration of prey species (Wenger et al., 2016). Since many fish

species do not show good hearing abilities at frequencies as high as the 28 kHz flowmeter

signals (Ladich and Fay, 2013), it is reasonable to assume, that the flowmeter does not have a

large effect on their distribution. If prey species of harbour porpoises aggregate close to the

flowmeter, it could be that harbour porpoises try to get access to this important food source

despite high sound exposure levels. If the energetic benefit is high enough, harbour porpoises

could tolerate the exposure to these signals. Our simulation in FIG. 18 could show, that along

the entire width of the Elbe River, a period of 60 minutes is sufficient to induce a TTS and even

decreases with decreasing distance to the flow meters.

B. Effects on behaviour

Effects of anthropogenic noise are numerous and must not be restricted to injuries and death.

The introduction of underwater noise within the hearing range of harbour porpoises can also

elicit behavioural changes. This could be shown for example by Kastelein et al. (2014a), who

found behavioural changes, when a harbour porpoise in human care was exposed to pinger

signals. These devices are similar in the frequency range to the acoustic flowmeter. Harbour

porpoises reacted to the introduction of pinger signals by an increased swim speed and breathing

rate, jumping out of the water and increased distances to the transducer (Kastelein et al., 2014a).

Accordingly, it is likely that harbour porpoises are likewise disturbed by the flowmeters in the

port of Hamburg and try to avoid close distances. Such disturbance effects may even result in

decreased individual fitness and could lead to long-term population consequences (King et al.,

2015).

C. Management approach

The underwater measurements in the port of Hamburg and the following evaluation of potential

effects on harbour porpoises were conducted on behalf of the Hamburg Port Authority. The

outcomes of the project were presented to the responsible employees of HPA (Schaffeld et al.,

2018). Although the area of highest impact was limited to close distances of below 100 m and

in a very narrow beam, the HPA targeted at an improvement of the current situation. Due to the

lack of an established monitoring of harbour porpoises in the Elbe River, we do not have any

information if harbour porpoises regularly occur close to the acoustic flowmeters. Although

harbour porpoises were sighted up- and downstream the acoustic flowmeters (Wenger et al.,

2016) it could be the case, that passing the sound field affects harbour porpoises. That risk could

Conclusion

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be taken, if the expected benefit is high. We do not have detailed information on the overall

application of these devices in large river systems. In addition to this described flowmeter in

the port of Hamburg, the HPA runs two more flowmeters upstream the Elbe River (pers. comm.

HPA). The presence of harbour porpoise in this area is assumed lower, but the current database

is insufficient for reliable estimates. It could be also the case, that further flowmeters are applied

along the Elbe River or other river systems, which we are not aware of. It is reasonable to

assume, that harbour porpoises have to pass further acoustic barriers during their annual

upstream travel. Our results demonstrate that the risk for a TTS is highest in a comparably small

area up to 74 m from the source. This leads to the conclusion that travelling harbour porpoises,

which want to pass this acoustic field should rather travel in the middle of the Elbe River.

However, this outcome raises the need for an adjustment of the acoustic flowmeter. Since the

Elbe River is highly exposed to ship traffic with vessels of all kinds, which travel in the middle

of the river, harbour porpoises could be forced to elude closer to the riverbanks, where the

flowmeters are. Unfortunately, this is the area with highest levels of the acoustic flowmeter and

the highest potential to induce a TTS. Since this combination of simultaneous harbour porpoise

and vessel presence is a problem, the HPA decided to adjust the source levels of the flowmeters.

Following the provided evaluation, the HPA instructed a reduction of the flowmeter source

levels.

IV. Acknowledgement

We would like to thank the Hamburg Port Authority for funding this project. We would also

like to express our gratitude to the team of the vessel “Reinhard Woltman” who supported us

during the measurements of underwater noise.

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Conclusion

I. Evolution of noise mitigation

Anthropogenic noise pollution has been recognized as one of the most hazardous forms of

pollution, which is omnipresent in all terrestrial and aquatic ecosystems (Andrew et al., 2002;

World Health Organization, 2017) leading to environmental changes, which are considered as

a key threat to biodiversity at an unpredictable scale (Kunc et al., 2016). The introduction of

underwater noise arises from the industry, e.g. during the construction and operation of offshore

wind farms (OWFs) (Brandt et al., 2018; Dähne et al., 2013; Graham et al., 2019) or shipping

(e.g. reviewed in Erbe et al., 2019) as an unintended by-product. The clearance of unexploded

ordnance from World War II represents a further unintended but regularly occurring noise

source (von Benda-Beckmann et al., 2015). Anthropogenic noise pollution occurs, however,

also on purpose for seismic explorations of the seafloor (e.g. Sarnocińska et al., 2020), military

sonar (Curé et al., 2016; Filadelfo et al., 2009; Isojunno et al., 2016) or to acoustically deter

animals (Brandt et al., 2013b, 2013a; Götz and Janik, 2013).

The understanding of effects of noise on marine life evolved over the last decades and is still

scarce. Only 14 years ago an intensely discussed research project ended, investigating the large-

scale thermal fields in the North Pacific Ocean by sending intense acoustic low frequency

signals over large distances without any prior risk assessments for marine life (Dushaw et al.,

2009). This study examined thermal trends by measuring the travel time of sounds between

measuring positions thousands of kilometres away, taking advantage of the correlation between

speed of sound and temperature (Dushaw et al., 2009). The acoustic thermometry of ocean

climate (ATOC) is just one example, which vividly displays the naive emission of underwater

noise without considering potential effects on the marine environment. Only recently, potential

effects of noise pollution awakened awareness. A relationship between the emission of

underwater noise and biological implications was first reported in 1974 after the stranding of

four Cuvier’s Beaked Whales (Ziphius cavirostris) in the Caribbean, which was suspected to

be a result from some kind of underwater explosion (van Bree and Kristensen, 1974). Various

mass stranding events of beaked whales e.g. in Greece in 1996, in the Caribbean in 1998 or the

Bahamas in 2000 led the international Whaling Commission’s Scientific Committee explain

that “there is now compelling evidence implicating military sonar as a direct impact on beaked

whales in particular” (reviewed in Simmonds et al., 2014). A great step forward in noise

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regulation was achieved by the identification of the mechanism of the “gas and fat embolic

syndrome” as the underlying mechanism of noise-related mortalities in beaked whales (Cox et

al., 2006). This mechanism causes haemorrhaging around the brain and lesions in vital organ

tissues, which were identified in several cases of stranded cetaceans and were accordingly under

suspect to be caused by the exposure to intense acoustic signals (Fernández et al., 2005; Jepson

et al., 2003; Siebert et al., 2013).

Despite military activities, further anthropogenic noise sources contribute to the noise pollution,

including impulsive noise from seismic surveys (Bain and Williams, 2006; Sarnocińska et al.,

2020) and pile driving strikes, generated during the construction of offshore wind farms (Brandt

et al., 2018; Dähne et al., 2013), together representing the most prominent contributors. The

effect of impulsive noise on harbour porpoise hearing was first investigated by Lucke et al.

(2009) after it was suggested to define noise exposure criteria for marine mammals (Southall et

al., 2007). These were based on data from bottlenose dolphins (Tursiops truncatus) and belugas

(Delphinapterus leucas), which were assumed to be questionable in transferability for high

frequency hearing cetaceans like the harbour porpoise (Southall et al., 2007). The exposure to

airgun pulses induced a TTS in a harbour porpoise in human care, if received levels exceeded

164.3 dB re 1 µPa²s (Lucke et al., 2009), showing that harbour porpoises are more sensitive to

impulsive noise than assumed (Southall et al., 2007). The measured TTSonset was subsequently

adopted in a regulation of noise mitigation during the construction of offshore wind farms in

Germany by the Federal Ministry for the Environment, Nature Conservation, and Nuclear

Safety (BMU, 2014). This comparably fast implementation of the TTSonset in noise mitigation

regulations clearly demonstrates the willingness to regulate underwater noise, but it has to be

taken into account that therefore reliable thresholds are neccessary. Although this is a good

example for a regulation of underwater noise, it might still be insufficient to prevent a TTS

from pile driving noise in harbour porpoises (Kastelein et al., 2015a, 2016). Moreover, to date

further anthropogenic noise sources remain unregulated.

This thesis aimed to assess the effect of anthropogenic noise pollution from different sources

on harbour porpoise hearing. The three chapters represent an evolution of the understanding of

noise effects. The introduction of underwater noise occurs in different scenarios, which can be

on purpose or unintended, some are already regulated or are tried to be regulated or even

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replaced by alternatives. The contributions of this thesis demonstrate that improvements in

noise mitigation are required in all of these exemplified scenarios of noise pollution.

A. Unintended effects of underwater sound application

The field of research regarding potential effects of anthropogenic underwater noise is relatively

new. This could be the reason why acoustic devices are still in use without considering potential

biological effects, which is exemplary shown in chapter 3). The results of this thesis illustrate

that the acoustic flowmeters in the port of Hamburg emit signals with sufficient energy to

induce a temporary threshold shift (TTS) in harbour porpoises. The onset of a TTS (TTSonset)

was determined at a received sound exposure level (SEL) of 138 dB re 1 µPa²s for a tonal

signals with a peak frequency of 28 kHz. The cumulative sound energy levels an animal could

receive from the acoustic flowmeter sound signals can be as high as a maximum of

165 dB re 1 µPa²s. Accordingly, up to a distance of 72 m from the sound source (which

corresponds to a distance to the border of 60 m) received SELs exceeded the TTSonset. Results

from the simulation approach demonstrate that received cumulative sound exposure levels for

harbour porpoises travelling along the flowmeter can be as high as 165 dB re 1 µPa²s. The

received levels for harbour porpoises, which travel along the flowmeter are found to be highly

variable. This is due to the high directionality of the flowmeters and the pulse interval of 4.2 s.

Results demonstrate that the risk for a TTS is highest in a comparably small area up to 72 m

from the source. This leads to the conclusion that travelling harbour porpoises, which want to

pass this acoustic field are well-advised to rather travel in the middle of the Elbe River.

However, this outcome raises the need for an adjustment of the acoustic flowmeter. Since the

Elbe River is highly exposed to ship traffic with a high variety of different vessels types, which

travel in the middle of the river, harbour porpoises could be forced to elude closer to the

riverbanks. Unfortunately, this is the area with highest levels of the acoustic flowmeter and the

highest potential to induce a TTS. Since this combination of simultaneous harbour porpoise and

vessel presence is a problem, switching off the flowmeter in the presence of vessels could be

an option. A good solution could be a dynamic switch, which recognizes increased background

noise caused by vessels and then turns off the flowmeter.

Furthermore, the necessity for emitting signals at such high pulse rates of 4.2 s from each side

is doubtful. Therefore, the pulse rate could be adjusted to a temporal resolution needed for

determination of flow speed trends. In this case, the source levels need to be increasing

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gradually, if the pulse rate decreases. This is necessary to prevent, that harbour porpoises are

surprised by a high intense signal at close ranges. The advantage of the currently high source

levels and short pulse intervals is that travelling harbour porpoises can hear the signal at

sufficient distances and are warned previously. In theory, this reduces the probability that

harbour porpoises enter the area of highest energy. A possible adjustment could be that the flow

speed is measured on an hourly basis. A measurement could start with signals of reduced

energy, which are gradually increased at steps of 3 dB, giving the harbour porpoise time to flee.

For instance, the sound exposure level could start at 102 dB re 1 µPa²s and will be increased at

steps of 3 dB each 4.2 s. After the emission of 13 signals, corresponding to 50 s, the TTSonset

will be exceeded. This would give the harbour porpoise sufficient time to leave the area of

highest intensity, until the actual flow velocity measurement starts. To my understanding, such

an adjustment represents an effective noise regulation and should be considered, if technically

feasible. The underwater measurements revealed that the acoustic flowmeters on the northern

and southern bank of the Elbe River were misaligned. Accordingly, an adjustment of the

orientation could allow for lower source levels, without any loss in quality of the results.

The outcomes of chapter 3 cast a new light on the thoughtless application of acoustic devices.

This raises the question, if this is just a rare example of thoughtless noise pollution or if this

happens also in other situations. From the results of chapter 2, it is clear, that this is not the only

example. Seal scarers were likewise naively introduced to prevent a TTS from pile driving

events (BMU, 2014), without a careful evaluation of further effects. It could be demonstrate,

however, that these devices have the potential itself to induce a hearing shift. This needs to be

considered in any future applications of seal scarers. As a further example, there is a demand

for an alternative to seismic airguns to locate deposits of fossil fuels in the seafloor, since

airguns can impair harbour porpoise hearing (Lucke et al., 2009) or affect behaviour of marine

mammals (Sarnocińska et al., 2020). Recent developments have yielded at alternative marine

seismic sources with expected reduced environmental impacts while maintaining efficiency

(Duncan et al., 2017; Pramik, 2013). The marine vibroseis could represent such an alternative

to airgun arrays. The emitted signals are of lower amplitude, longer duration and smaller

bandwidth than airgun pulses (Pramik, 2013; Tenghamn, 2006). Since most of the energy is at

frequencies below 200 Hz and amplitudes are lower, the potential to induce a TTS is assumed

to be lower than for airguns (Duncan et al., 2017; Pramik, 2013). However, the acoustic signals

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are of longer duration than airgun signals and the sound exposure levels could be similar. In

addition, these signals consist of tone sweeps at frequencies below 100 Hz (Duncan et al., 2017;

Tenghamn, 2006). The combination of longer durations and tones at certain frequencies

increases the potential to mask biologically relevant signals (reviewed in Erbe et al., 2016).

These frequencies overlap with the typical frequency range of blue or fin whale communication

(Širović et al., 2007). Before such devices are applied on a wide scale, potential effects have to

be investigated to exclude that marine life is affected. This is done, for instance, in an ongoing

project of the Institute for Terrestrial and Aquatic Wildlife Research with blue whale sound

exposure experiments in Iceland.

The outcomes of this dissertation emphasize the need for a general previous authorization

process prior to the use of underwater sound for any purpose with potential effects on aquatic

life. It has to be considered that potential effects for target and non-target species are carefully

reviewed.

B. Naive implementation of underwater sounds

The example described in chapter 2) demonstrates an approach to deter marine mammals out

of a certain area by introducing of special underwater sounds. Acoustic deterrent devices are

widely used to counteract the economic loss by seal depredation (Dawson et al., 2013; Götz

and Janik, 2013) around aquacultures or to deter harbour porpoises out of the vicinity prior to

pile driving events (Brandt et al., 2013a). The outcomes of chapter 1 clearly confirm that prior

deterrence is substantially needed to protect harbour porpoises from a TTS appearing after the

reception of multiple pile driving strikes. However, this thesis also confirms the potential of a

single seal scarer signal to induce a TTS in harbour porpoises at estimated distances between

211 m and 5.9 km. These contradictory outcomes indicate the need for a thorough regulation

of underwater noise emissions during the construction of offshore wind farms, which needs to

be adopted in noise protection concepts (e.g. BMU, 2014). Therefore, source levels need to be

down regulated and slowly increased, giving harbour porpoises enough time to flee, when

applied as a regulation to prevent TTS. In order to minimize temporary habitat loss and potential

food sources, the source levels of ADDs must be adjusted to the desired deterrence range. One

limitation of our suggested implementation is the gap of knowledge concerning a reliable

correlation between deterrence range and received levels.

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In addition to the application as a mitigation tool, the results raise the need for a regulation in

form of an authorization process and monitoring for the application of seal scarers around

aquacultures. Although ADDs are a significant and chronic source of underwater noise

pollution along the Scottish west coast around aquacultures with a steady increase in ADD

usage and substantial geographic expansion (Findlay et al., 2018), neither a license is required

to deploy these devices nor any statistics on the usage exist (Coram et al., 2014). ADDs were

deployed to counteract economic loss by seals. The observed deterrence of harbour porpoises,

which accompanies their usage, has been regarded as a comparatively benign side effect

(reviewed in Götz and Janik 2013). Nevertheless, the introduction of ADD signals significantly

influences the quality of a habitat and should be therefore considered in the evaluation of the

environmental status in the Marine Strategy Framework Directives (MSFD) on a European

level (Tasker et al., 2010). The extensive usage of ADDs around marine aquacultures represents

a local major source of chronic anthropogenic noise pollution, which has to be addressed in

national marine registries to meet international protective agreements, e.g. MSFD and Oslo and

Paris Convention (OSPAR) (cited from Findlay et al., 2018). Regarding the previously reported

behavioural responses of harbour porpoises to seal scarer signals, such as increased swim speed,

porpoising behaviour, increased breathing rates (Kastelein et al., 2015c), but also the exclusion

from habitats (Brandt et al., 2013a) can be assumed to pose a high risk for chronic stress and

potential cumulative effects on general health. Nevertheless, these effects are evaluated to date

as insufficient arguments to regulate the use of ADDs (Coram et al., 2014; Findlay et al., 2018).

The evidence provided in chapter 2 of this thesis that a TTS or even PTS can be induced should

lead to the development of a regulation system.

C. Established concept for noise mitigation

Chapter 1) is dedicated to the mitigation of pile driving noise, which was recognized as a threat

for harbour porpoise hearing (Lucke et al., 2009) and a concept for regulation was already

introduced six years ago (BMU, 2014). Nevertheless, this thesis could show that further

measures are urgently needed to consider the TTS potential from multiple exposure.

Regarding the protection of harbour porpoises, Germany has enforced the strictest regulations

in the EU to date. Single pile driving strikes must not exceed a SEL of 160 dB re 1 μPa²s at a

distance of 750 m, in order to prevent a temporary threshold shift. Regarding a TTS as an injury

is outstanding, since most other European countries and the United States of America consider

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a PTS as an injury and regulate noise accordingly (reviewed in Stöber and Thomsen, 2019).

Furthermore, wind farm operators are obliged to deter harbour porpoises prior to pile driving

activities and to use a soft start procedure with limited hammer force and longer pulse intervals

in the beginning of pile driving, following German regulations (BMU, 2014). However, current

regulations do not consider the evident TTS potential from the exposure to multiple pile driving

strikes, which previously has been scientifically proven (Kastelein et al., 2015a, 2016). This

thesis provides a novel evaluation tool, which allows estimating the TTS potential for harbour

porpoises, fleeing during pile driving activities, representing a significant contribution to an

effective protective noise regulation. This tool considers current knowledge on TTSonset for

multiple pile driving strikes, harbour porpoise swim speed capacity and sound propagation of

pile driving strikes in a shallow region in the German North Sea. One of the key benefits of this

evaluation tool is that all applied variables are easy to adjust for different soundscapes or for

different TTSonsets. The simulation approach of chapter 1 supports current noise mitigation

regulations during the construction of OWF in Germany as a valuable measure for protecting

harbour porpoises not only from single but also from multiple pile driving strikes.

Based on this simulation approach, only the combination of restricting the maximum single

strike sound exposure level (SELSS) to 160 dB re 1 µPa²s at a distance of 750 m, a previous

deterrence and a soft start with reduced energy and longer pulse intervals allow harbour

porpoises to avoid a TTS from multiple exposures. To my understanding, there is no reason to

question the current single strike regulation. This simulation approach highlights the need for

considering also the introduced minimum deterrence distance (MDD). The MDD corresponds

to a distance, a harbour porpoise must be at least deterred prior to any pile driving activity for

being able to escape from a TTS by a continuous flight. The MDD is mostly depending on the

possible swim speed of harbour porpoises, the source level and sound propagation. A MDD of

2.4 km was determined for harbour porpoises, which are capable of swimming at a speed of

6.1 m s-1 and even of 4.7 km for harbour porpoises fleeing at a speed of 0.9 m s-1. Any tolerated

increase in maximum levels of single pile driving strikes exceeding the 160 dB re 1 µPa²s at a

distance of 750 m would substantially affect the already large minimum deterrence distance.

This dissertation aims for raising the attention for further critically needed studies, which tackle

the gap of an empirical based effective quiet threshold (EQT). In the absence of such a

threshold, a proxy was considered, named “still higher than effective quiet threshold” (SHEQ).

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As a best guess, the lowest SELSS, which has been proven to induce a TTS, was chosen as the

SHEQ. This emphasizes the need for a real effective quiet threshold, which determines the safe

distance for harbour porpoises, where a TTS cannot be induced. The absence of an EQT

constraints the ability to regulate mandatory minimum deterrence distances.

A challenging problem of this simulation approach is that equal energy does not automatically

have to generate the same amount of TTS, because the TTSonset is depends on the duty cycle,

the SPL and the received SELcum (Kastelein et al., 2015b, 2014b). Regarding our simulation

approach we assume, that the TTSonset for fleeing harbour porpoises could be lower than the

proposed value of 175 dB re 1 µPa²s, which derives from a study with constant exposure to

single strikes with an SEL of 145 dB re 1 µPa²s (Kastelein et al., 2016). However, a fleeing

harbour porpoise would receive pile driving strikes with decreasing SELSS and increasing

distance to the sound source. In contrast to Kastelein et al. (2016), the harbour porpoise would

receive multiple strikes with variable SELSS, which are all above the SELSS in that playback

experiment. To my knowledge, no study has yet yielded at a TTSonset for varying or decreasing

SELSS over time.

II. Outlook

The analyses in this thesis raise further research questions, which should be addressed in future

projects:

A. Acoustic flowmeter

The Elbe River is highly exposed to ship traffic, which contribute significantly to the

underwater soundscape. However, this area is most likely of high ecological importance for

harbour porpoises and provide a great benefit, because harbour porpoises regularly occur in this

noisy area. Future studies should investigate the habitat usage of harbour porpoises in this area

to determine its ecological importance. Currently no systematic monitoring of harbour

porpoises in large river systems exists, although regularly sightings are reported (Wenger et al.,

2016; Wenger and Koschinski, 2012). A monitoring is substantially needed for harbour

porpoises, which are protected throughout their range, for better understanding the driving

factors for entering rivers. In addition to potential hearing impairments, these devices can also

induce behavioural changes or affect harbour porpoise migration. It is reasonable to assume,

that entering the sound field elicits discomfort or stress in the animals. In this case, the acoustic

flowmeter could create a barrier effect. Future research should focus on a potential barrier effect

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and habitat exclusion. Furthermore, this acoustic flowmeter in the port of Hamburg is most

certainly not the only position, where the water flow is measured. It is reasonable to assume

that multiple, more similar devices emit acoustic signals in larger river systems like the Elbe or

Weser River. Information on the existence of additional acoustic flowmeters should be

collected in future studies, since these could represent a source of potential injury for present

harbour porpoises (Wenger and Koschinski, 2012). To the best of my knowledge, there is no

prior approval procedure needed to apply these acoustic devices. A legal obligation for the

introduction of underwater noise with the potential to induce hearing impairment for harbour

porpoises should be carefully considered. This possible barrier with a TTS potential should be

also addressed for harbour seals, since these animals also occur in this area and are capable of

hearing the acoustic flowmeter signal (Kastelein et al., 2009a, 2019a). Habitat exclusion is most

likely for seals, since the frequency of the flowmeter signal is represented also in signals of

acoustic deterrent devices and should therefore be considered in future research.

B. Acoustic deterrent devices

A large selection of different acoustic deterrent devices exists with an increasing field of

application possibilities. Available devices differ in signal amplitude, frequency and duration

or duty cycle. This increases the necessity to examine their potential to induce a TTS in harbour

porpoises or other marine mammals. In order to prevent side effects on non-target species,

hearing abilities of these species should be considered in the development of ADD signals. This

will become even more important, if the field of application increases, for example as a

deterrent device prior to the clearance of unexploded ordnance of World War II in German

waters. Additionally, dose responses of received levels and resulting deterrence ranges, should

be investigated to adjust the source levels of ADDs to the deterrence range desired. Reported

deterrence ranges are highly variable and do not allow for reliable estimates of dose responses

to date (reviewed in Götz and Janik 2013).

III. Future directions of TTS research

A. Biological mitigation as a regulation approach

Another novel finding is the ability of at least four toothed whales to actively attenuate auditory

brainstem responses, which is believed to serve as a protective mechanism (Finneran, 2018;

Nachtigall et al., 2016, 2017; Nachtigall and Supin, 2014). This conditioned “self-mitigation”

in the expectancy of an intense sound exposure, led to elevated hearing thresholds up to 40 dB

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(Finneran, 2018). This conditioned mechanism is believed to protect from outgoing

echolocation clicks, which contain very high source levels, but also from an expected exposure

to underwater noise (Finneran, 2018; Nachtigall et al., 2017). This conditioned attenuation is

most efficient, if the animals expected a following intense exposure. This raises the question, if

the ability of self-mitigation can serve, to protect from anthropogenic noise effects. Based on

the current knowledge, a previous signal would be needed to warn animals, for example before

pile driving activities start. To date it is not possible to reliable estimate, how many conditioning

trials are needed to develop a protection against an impending sound. Furthermore, harbour

porpoises are believed to use large spatial areas, so animals in the surrounding area could be

“conditioned” or are still naive. The main limitation is the lack of knowledge about the

underlying mechanism of this conditioned attenuation, which does not allow for reliable

estimates of effectiveness and duration. It also remains unsolved to date, if such a mechanism

derives from middle ear (conductive) mechanisms or from a neural mechanism involving

efferent inhibitory projections (Finneran, 2018; Nachtigall et al., 2017). Further research is

needed to assess these limitations and to determine, if any impairment still occurs, which cannot

be seen by measuring the hearing threshold. Current knowledge is insufficient to consider this

described self-mitigation as a tool to prevent TTS.

B. Understanding of TTS

This thesis provides scientific evidence for a TTS potential from a single exposure to seal scarer

signals. However, this evaluation cannot reliably estimate a TTS potential for the reception of

multiple signals. Regarding the randomization of inter pulse intervals of seal scarers at intervals

between 0.6 and 90 s (cited in Mikkelsen et al., 2017), a TTSonset cannot be estimated without

the understanding of the relationship between TTS growth and exposure variables like SPL,

duty cycle and cumulative SEL. This represents also a limitation for the simulation approach

of chapter 1. The TTSonset, which was applied in the simulation approach (Kastelein et al.,

2016), derives from an experiment with a repeated exposure to signals of the same source level.

In the case of a fleeing harbour porpoise, the received levels are expected to decrease over time,

when the distance to the sound source increases. Based on current knowledge about TTS in

harbour porpoises, it is reasonable to assume that a TTSonset from a multiple exposure could be

lower, if the received levels start higher and decrease over time. The relationship between

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received levels, duty cycles and corresponding TTS growth in cumulative exposures should be

addressed in future studies. This would represent a huge step in estimates of TTS potential.

C. Ecological relevance of temporary threshold shifts

This study investigated the potential of different anthropogenic noise sources to induce a TTS

in harbour porpoises, which is a common approach to assess the effect of noise pollution

(reviewed in Finneran, 2015). However, the implications of a TTS remain unknown to date.

Future studies are critically needed to determine the ecological relevance of a temporary hearing

shift. To the best of the author’s knowledge, no one was able to determine ecological

consequences of hearing impairment to date, although no one would question that harbour

porpoises critically rely on hearing. Echolocation is a very high-evolved specialisation towards

living in a niche environment (Fenton et al., 2014). Any interference in acoustic perception can

reduce the small advantage of predators and could have strong effects on their survival.

Assuming that harbour porpoises show a low resilience to any disturbance, which could be

represented by their continuous foraging to maintain energetic demands, any disturbance might

have severe effects (Wisniewska et al., 2016). This situation is aggravated by the health status

of harbour porpoises in the German North- and Baltic Sea, which show a high prevalence for

parasites in lungs and ears as well as associated bronchopneumonia (Lehnert et al., 2005; Morell

et al., 2017b; Siebert et al., 2001). Most of the risk assessment studies assume a healthy

population, which is not the case. This gap of knowledge strengthens the need for further

research on infectious agents and other pathological findings, which might affect hearing

abilities (Morell et al., 2017b; Prahl et al., 2011; Wohlsein et al., 2019) and potentially the

ability to recognize possible threats, such as set-nets (Kastelein et al., 2000; Villadsgaard et al.,

2007). Further insight into ecological effects of TTS, stress responses and the health status of

harbour porpoises could help to shed light on the dramatic situation of harbour porpoises, which

often die before females are sexually mature (Kesselring et al., 2019).

To date, the consequences of a temporal hearing shift at 4 (Lucke et al., 2009), 8 (Kastelein et

al., 2016), 14 or 28 kHz (Schaffeld et al., 2019) for harbour porpoises are unknown. Thus,

assumptions about ecological relevance would be highly speculative. These comparably low

frequencies are all in the hearing range of harbour porpoises but far away from the range of best

hearing, which is around 130 kHz (Kastelein et al., 2002, 2010; Ruser et al., 2016a),

corresponding to the frequency of echolocation clicks (Møhl and Andersen, 1973; Villadsgaard

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et al., 2007). However, it is reasonable to assume, that hearing lower frequencies is of

highimportance for harbour porpoises, because it was preserved in evolution, when

echolocation ability and high frequency hearing evolved. The actual cause for this ability

remains unknown, giving the chance to hypothesize and develop further research ideas. A

possible explanation could be, that acoustic signals of predators should be recognized in order

to elicit antipredator behaviour, like it has been shown for multiple cetaceans exposed to

predator signals (Aguilar de Soto et al., 2020; Bowers et al., 2018; Curé et al., 2013; Jacobson

et al., 2015; Rankin et al., 2012). Actually, in the absence of regularly occurring killer whales

or bottlenose dolphins in German waters as typical predators of harbour porpoises, the predation

of grey seals on harbour porpoises has been revealed recently (Bouveroux et al., 2014; Heers et

al., 2018; Jauniaux et al., 2014; Leopold et al., 2015). This marine top predator of German

waters is highly vocal underwater, especially within the breeding season (Asselin et al., 1993),

and harbour porpoises could take advantage of acoustic cues to avoid them.

The ability to hear lower frequencies can also support harbour porpoises in their ability to find

prey by passive listening. Likewise, bottlenose dolphins elicited attraction to playbacks of

soniferous fish signals (Gannon et al., 2005), which represent a large amount of their diet

(Burros and Myrberg, 1987). The ability to localize prey by passive listening could be of high

importance for harbour porpoises since their echolocation beam is highly directional and

adapted for short distance localization (Koblitz et al., 2012). Eavesdropping on fish, which were

found to acoustically communicate to a large extent (reviewed in Ladich, 2019), could help to

find prey over larger distances. This could be very advantageous in a seemingly endless

environment with patchy distributed prey at decreasing densities. Future research should

investigate, if harbour porpoises take advantage of passive listening to find prey. If it turns out

that harbour porpoises use low frequencies to find prey, the effect of masking becomes more

important than previously assumed. Masking is believed to be of less importance for harbour

porpoises, since echolocation signals are at much higher frequencies than anthropogenic noise

pollution occurs. However, if a dependence on low frequent fish sounds exist, these biological

relevant signals are likely overheard in the presence of high background noise levels.

In addition to potential effects of masked low frequency signals, harbour porpoises could be

distracted by the presence of a TTS. Likewise, hearing impaired human listeners perform worse

in distinguishing two different simultaneous heard messages, if ambient noise increases,

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although no differences to the normal hearing group can be seen in situations of low ambient

noise (Best et al., 2010). If this is also the case for harbour porpoises, the ecological relevance

of a TTS might dramatically increase due to the high levels of noise pollution in the areas

inhabited by harbour porpoises.

The prevention of a TTS is usually proclaimed as a management goal in underwater noise

regulation (e.g. in Germany, BMU 2014). From a conservation perspective, this precautionary

approach is preferred above trying to prevent permanent shifts like in different countries (e.g.

U.S. Marine Mammal Protection Act in the United States). However, it is not clear, if this

protection is sufficient. Conventional reporting of hearing impairment is limited to

measurements of hearing thresholds (reviewed in Finneran 2015) or hair cells (Morell et al.,

2017a). Nonetheless, a hearing impairment in humans can also be reflected in decreased

auditory evoked potentials, which remain undetected when measuring hearing thresholds and

are therefore referred to as a “hidden hearing loss” (Kujawa and Liberman, 2015; Lobarinas et

al., 2017). This can be a result of a permanently decreased number of synaptic connections

between the inner hair cells and auditory nerve fibres (Le Prell, 2019). Noise exposures,

however, which induce reversible thresholds shifts can lead to permanent cochlear

synaptopathy, which can have compounding effects for hearing in situations with elevated noise

levels (Kujawa and Liberman, 2015). These findings raise the concern, that a TTSonset could be

an insufficient indicator for protective regulations. Further research is needed to firstly

determine, if temporary threshold shifts can also lead to decreasing auditory evoked potentials

in harbour porpoises, and secondly to investigate its effect on acoustic perception.

A threshold for hearing impairment, either temporary or permanent, serves as a template for

noise regulation. However, the ecological consequences of such a TTS are not understood yet.

Further experiments are critically needed to determine effects of a TTS on the echolocation

performance of harbour porpoises. This information is critically needed to estimate

consequences on the energy budget or health of individuals and on the long run for the

population. As an experimental approach, harbour porpoises could be trained to perform

working tasks like object discrimination, catching fish or navigating blindfolded, while a TTS

is simulated. Such a simulation could be achieved by the development of an acoustic filter,

designed to damp certain frequencies, which could be attached to the animal around the jaw.

Conclusion

106

Animals could then be trained to perform certain tasks, which are evaluated in efficiency

compared to trials with normal hearing.

This study represents an important contribution for the implementation of protective directives

but also for the improvement of existing directives.

Summary

107

Summary

Tobias Schaffeld - Effect of anthropogenic underwater noise on harbour porpoise hearing in

areas of high ecological importance

Although aquatic noise pollution has been recognized as a key threat to biodiversity at an

unpredictable scale, the scientific discussion about effects on marine life has just evolved over

the last decades and is ongoing. Anthropogenic underwater noise occurs as an unintended by-

product, e.g. from shipping or construction work, but can also be on purpose, e.g. to deter

marine mammals or for acoustic localisation with sonars. Especially the evaluation of the

impacts on marine wildlife is in focus in modern science.

The species of interest in this thesis is the harbour porpoise (Phocoena phocoena), as the only

cetacean representative in German waters. Beyond that, these animals are particularly

vulnerable to interferences by noise due to their dependence from acoustically sensing their

environment. They demonstrate a very low resilience to disturbance, as they need to forage

almost continuously to maintain their high energy demands. The main goal of this thesis is to

assess the effect of noise disturbance from different sources as an antagonist, interfering with

acoustic perception of the habitat. This helps to shed light on gaps in noise regulation and raises

attention to the naive application of acoustic devices. This thesis comprises evaluations of three

different noise sources with potential effects on harbour porpoise hearing.

Firstly, to reveal the potential of multiple pile driving strikes to induce a temporary threshold

shift (TTS) under current German noise regulations, simulation approaches were conducted.

During the construction of an offshore wind farm underwater noise was recorded and sound

exposure levels (SEL) of single strikes were determined. This served for modelling the sound

propagation. Current noise regulations target single strikes up to a distance of 750 m for

preventing a TTS. However, the modelled sound field demonstrates that pile driving strikes at

distances up to 5.4 km contain sufficient energy, to induce a TTS after a repeated reception.

The “minimum deterrence distance” (MDD) was introduced as a novel protective unit, which

was determined between 2.3 and 4.7 km for four tested swim speed levels. The MDD marks

the minimum distance to the pile driving site, at which an animal must located, to be able to

escape a TTS by a flight. The simulation approach supports the current noise regulation in

Germany with a single strike SEL, a soft start and prior deterrence with seal scarers.

Summary

108

Secondly, a seal scarer was tested for its potential to induce a TTS in harbour porpoises. Hearing

tests with a harbour porpoise in human care prior to and after the exposure to artificial seal

scarer signals were conducted. The fatiguing signal consisted of a 0.5 s pure tone at 14 kHz

with four octave overtones with decreasing amplitudes. Hearing thresholds were measured by

monitoring the auditory evoked potential (AEP) response. Exposures exceeding a sound

exposure level of 142 dB re 1 µPa²s induced a significant TTS at a hearing frequency of 20 kHz

and at 28 kHz for SELs above 147 dB re 1 µPa²s. Assuming a theoretical transmission loss

between cylindrical and spherical spreading, a TTS could be induced at distances between

211 m and 5.9 km by a single exposure. Based on these findings a down-regulation of seal

scarer source levels was recommended.

Thirdly, an acoustic flowmeter (AFM) was evaluated in the port of Hamburg for its potential

to induce a TTS in harbour porpoises. The Hamburg Port Authority initiated this project after

several dead harbour porpoises stranded in this area of the Elbe River. These animals could be

forced in hazard areas by passing vessels, which occur in high numbers in this area. Therefore,

AFM signals were recorded underwater on board of a vessel for modelling the acoustic field.

The AFM transmits short signals with a peak frequency at 28 kHz in a highly directional beam

and at a pulse rate of 4.1 s from two positions at opposite sides of the river. A TTSonset for a

single exposure was derived from sound exposure experiments with an animal in human care

and for multiple exposures suggested from literature. A maximum SEL of 165 dB re 1 µPa²s

was determined. Single pulses exceeded the SEL-TTSonset of 138 dB re 1 µPa²s up to distances

of 72 m. The reception of multiple pulses was simulated for travelling harbour porpoises. The

received levels are highly variable due to the timing and high directionality of the AFM.

Although hazard zones are comparably small and signals are assumed to be heard at large

distances, a down-regulation of the AFM source level was suggested.

Within the three presented chapters of this thesis, an evolution of the understanding noise

effects could be shown. The introduction of underwater noise can be on purpose or unintended,

is already regulated or its regulation is currently in progress as well as possibly replaced by

alternatives. The contributions of this thesis demonstrate that improvements in noise mitigation

are required in all of these exemplified scenarios. This thesis complements studies assessing

the potential to induce a TTS. Far more important it will help to find the right starting point,

Summary

109

where adjustments in regulations are most effective. Moreover, the presented studies indicate

gaps in the understanding of TTS, which should be addressed in future research.

Zusammenfassung

110

Zusammenfassung

Tobias Schaffeld - Einfluss anthropogener Schalleinträge auf das Gehör von Schweinswalen

in Gebieten von hoher ökologischer Bedeutung

Die durch den Menschen verursachte Lärmverschmutzung in den Meeren stellt eine erhebliche

Bedrohung unvorhersehbaren Ausmaßes für die Biodiversität dar. Die wissenschaftliche

Auseinandersetzung mit möglichen Auswirkungen von Lärm auf marine Organismen findet

erst seit kurzem statt und ist noch lange nicht abgeschlossen. Anthropogener Unterwasserlärms

entsteht unter anderem als unbeabsichtigtes Nebenprodukt der Schiffverkehr oder durch

Bauarbeiten. Akustische Signale werden aber auch gezielt verwendet um Meeressäuger zu

vergrämen oder zur Navigation mit Sonaren.

Die in dieser Dissertation behandelte Zielart ist der Schweinswal (Phocoena phocoena) als

einziger Vertreter der Wale in deutschen Gewässern. Als Vertreter der Zahnwale erfasst der

Schweinswal seine Umgebung mittels Echoortung akustisch, sodass eine große Abhängigkeit

von einem intakten Gehör besteht. Schweinswale reagieren dementsprechend besonders

sensibel auf Störungen durch Lärm. Da diese fast ununterbrochen jagen müssen, um ihren

hohen Energiebedarf aufrechtzuerhalten, wird von einer sehr geringen Resilienz gegenüber

Störungen ausgegangen. Die vorliegende Studie bewertet unterschiedliche Lärmquellen

hinsichtlich ihrer Funktion als Antagonisten der akustischen Wahrnehmung für Schweinswale.

Das Ziel richtet sich hierbei auf das Auffinden von Lücken in der aktuellen Schallregulierung

und der Schaffung eines Bewusstseins bezüglich der naiven Anwendung akustischer Geräte.

Zu diesem Zweck werden die möglichen Auswirkungen von drei unterschiedlichen

Lärmquellen auf das Gehör von Schweinswalen behandelt.

Als erstes wurde durch einen Simulationsansatz ermittelt, ob das aktuelle Schallschutzkonzept

für Rammarbeiten in Offshore Windparks einen ausreichenden Schutz bietet, um eine

temporäre Hörschwellenverschiebung (TTS), das heißt reversible Verschlechterung des

Gehörs, durch mehrere Rammschläge zu verhindern. Hierfür wurde während des Baus eines

Offshore Windparks (OWP) Unterwasserschall aufgenommen und die Schallenergiepegel

(SEL) von Einzelschlägen ermittelt, mit denen die Schallausbreitung modelliert werden konnte.

Die aktuellen Lärmschutzbestimmungen zielen darauf ab, eine TTS durch Einzelschläge bis in

eine Entfernung von 750 m zu verhindern. Das modellierte Schallfeld zeigt jedoch, dass

Zusammenfassung

111

Rammschläge in Entfernungen von bis zu 5,4 km ausreichend Energie besitzen, um eine TTS

nach einer Mehrfachbeschallung auszulösen. Als neue Einheit zur Bewertung des

Gefährdungspotentials wurde die „minimale Vergrämungsdistanz“ (MVD) eingeführt, die für

vier getestete Schwimmgeschwindigkeitsstufen zwischen 2,3 und 4,7 km bestimmt wurde. Die

MVD markiert die Mindestentfernung zur Schallquelle, in der sich Schweinswale bei Beginn

der Rammarbeiten befinden müssen, um einer TTS durch Flucht zu entkommen. Der

Simulationsansatz unterstützt die derzeitig angewandte Lärmregulierung in Deutschland mit

einer begrenzten Maximalenergie für Einzelschläge, einem „soft start“ und einer vorherigen

Vergrämung mit Seal Scarern.

Im zweiten Teil wurde getestet, ob ein Seal Scarer das Potential besitzt, ein TTS bei

Schweinswalen zu induzieren. Hierfür wurden Hörtests mit einem Schweinswal in

menschlicher Fürsorge vor und nach der Exposition mit künstlichen Seal Scarer Signalen

durchgeführt. Das ermüdende Signal bestand aus einem 0,5 s langen 14 kHz Sinuston mit vier

Oktav-Obertönen mit abnehmenden Amplituden. Die Hörschwellen wurden anhand auditorisch

evozierter Potentiale (AEP) bestimmt. Schallexpositionen mit mehr als 142 dB re 1 µPa²s

induzierten eine signifikante TTS bei einer Hörfrequenz von 20 kHz und ab 147 dB re 1 µPa²s

bei 28 kHz. Unter der Annahme eines theoretischen Ausbreitungsverlusts zwischen

zylindrischer und kugelförmiger Ausbreitung könnte ein TTS in Entfernungen zwischen 211 m

und 5,9 km durch eine einzelne Exposition induziert werden. Basierend auf diesen Befunden

wurde eine Senkung des Quellschallpegels von Seal Scarern empfohlen.

Als Drittes wurde eine akustische Strömungsmessanlage im Hamburger Hafen hinsichtlich

ihres Potentials untersucht, eine TTS bei Schweinswalen hervorzurufen. Dieses Projekt wurde

von der Hamburg Port Authority initiiert, nachdem mehrere tote Schweinswale in diesem

Gebiet der Elbe strandeten. Der Schiffverkehr ist in diesem Bereich sehr hoch und

Schweinswale könnten durch vorbeifahrende Schiffe in den Gefahrenbereichen abgedrängt

werden. Die Unterwasserschallaufnahmen der akustischen Signale der Strömungsmessanlage

wurden an Bord eines Schiffes durchgeführt und das Schallfeld anschließend modelliert. Die

Strömungsmessanlage verwendet kurze Signale mit einer Frequenz von 28 kHz, die in einem

stark gerichteten Kegel und einer Pulsfrequenz von 4,1 s von zwei Positionen auf

gegenüberliegenden Seiten des Flusses emittiert werden. Ein TTSonset für eine

Einfachbeschallung wurde mittels Hörversuchen mit einem Tier in menschlicher Fürsorge

Zusammenfassung

112

ermittelt, während der Schwellenwert für eine Mehrfachbeschallung Literaturbasiert ist. Ein

maximaler SEL von 165 dB re 1 µPa²s wurde bestimmt. Einzelne Signale überschritten den

SEL-TTSonset von 138 dB re1 µPa²s bis in eine Entfernung von 72 m. Der Empfang mehrerer

Schallsignale wurde für Schweinswale simuliert, die an der Strömungsmessanlage entlang

wandern. Die empfangenen Pegel sind aufgrund des Timings und der hohen Richtwirkung der

Strömungsmessanlage sehr variabel. Obwohl die Gefahrenzonen vergleichsweise klein sind

und Schweinswale höchstwahrscheinlich die Signale in großen Entfernungen wahrnehmen

können, wurde empfohlen den Quellschallpegel zu senken.

In den drei vorgestellten Kapiteln dieser Arbeit konnte eine Entwicklung des Verständnisses

von Unterwasserlärmeffekten gezeigt werden. Der Eintrag von Unterwasserlärm kann

absichtlich oder unbeabsichtigt erfolgen, kann bereits reguliert sein oder es werden Versuche

zu deren Regulierung unternommen. Teilweise werden sogar Alternativen gesucht um

Lärmquellen zu ersetzen. Die Arbeiten in dieser Dissertation zeigen, dass in all den

vorgestellten Szenarien Verbesserungspotential in der Schallregulierung besteht. Diese Arbeit

erweitert den aktuellen Kenntnisstand in der Bewertung des Potenzials zur Auslösung einer

TTS, wird jedoch vor allem dazu beitragen, den richtigen Ansatzpunkt zu finden, an dem

Regulierungen am effektivsten sind. Die vorgestellten Studien zeigen Wissenslücken im

Verständnis von Hörschwellenverschiebungen bei Schweinswalen. Zukünftige

Forschungsvorhaben sollten sich diesen widmen.

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List of figures

133

List of figures

FIG. 1: Research area in the German North Sea with marked positions of underwater

recorders (triangle) and positions where pile driving activities were conducted (points).

.......................................................................................................................................... 21

FIG. 2: Third octave level spectrum of the analyzed pile driving events, color and symbol

coded for measuring position and pile. ............................................................................ 26

FIG. 3: Determined SELSS in dB (re 1 µPa²s) of pile driving activities during the construction

of 50 monopiles in the Amrumbank West OWF.............................................................. 27

FIG. 4: Simulation harbor porpoise fleeing from a certain start position (x-axis) up to the safe

distance (5604 m). ............................................................................................................ 31

FIG. 5: Radii of hazard zones around a pile driving site, where the TTSonset of 175 dB re 1

µPa²s can be exceeded by multiple events above the SHEQ of 145 dB re 1 µPa²s for

single strikes. .................................................................................................................... 32

FIG. 6: Tone pips, used as hearing stimuli. .............................................................................. 51

FIG. 7: Recorded frequency spectrum of one generated artificial seal scarer signal (top),

which was used for animal exposure................................................................................ 54

FIG. 8: Example of measured AEP for 8 sound pressure levels (colour coded) between 87 and

122 dB re 1 µPa. ............................................................................................................... 57

FIG. 9: Effects of seal scarer exposure (at 14 kHz, with four harmonics) on hearing thresholds

at 20 (black circles) and 28 kHz (grey triangles). ............................................................ 59

FIG. 10: Estimated hazard area where single seal scarers signals exceed the determined SPL

TTSonset of 155.2 dB (pp), corresponding to a SPL TTSonset of 146.2 dB re 1 µPa

(rms, dashed line). ............................................................................................................ 64

FIG. 11. Linear regression of SEL–SPL of all played back seal scarer signals during hearing

tests at 20 and 28 kHz. ..................................................................................................... 70

FIG. 12: Effects of seal scarer exposure on hearing thresholds at 20 (circles) and 28 kHz

(triangles). ........................................................................................................................ 71

FIG. 13: Study area in the Elbe River in the West of Hamburg. The positions of the

underwater flowmeters are shown by red triangles. ......................................................... 78

FIG. 14: Top view on the modelled sound field of the acoustic flowmeter on the north (top

row) and south (bottom row) riverbank. .......................................................................... 80

FIG. 15: Top view on the combined sound field of the two flowmeters at a depth of 5 m. .... 81

FIG. 16: Effects of 28 kHz tone exposure on hearing thresholds at 28 kHz (black circles). ... 86

FIG. 17: Received cumulative sound exposure levels (SELcum) on simulated transects along

acoustic flowmeters. ......................................................................................................... 88

FIG. 18: Required time within sound field to exceed cumulative SEL-TTSonset. .................... 89

List of tables

134

List of tables

TABLE I. Summary of variables and values used for the model. ........................................... 24

TABLE II. Simulation results for the maximum distance as a start position for a flight, where

a TTS could still be induced before reaching the safe distance. ...................................... 30

TABLE III: Application example of simulation approach, using the acoustic properties of pile

driving strikes reported by Dähne et al. (2017). ............................................................... 38

TABLE IV. Summary of the determined TTSonset after exposure to artificial seal scarer

signals. .............................................................................................................................. 60

TABLE V: Measured hearing thresholds, which have been used to calculate mean hearing

thresholds ......................................................................................................................... 68

TABLE VI. Measured hearing thresholds after exposure, which resulted in a significant

hearing shift, relative to the baseline. ............................................................................... 69

TABLE VII: Harbour porpoise positions on simulated flight tracks. ...................................... 83

Acknowledgement

135

Acknowledgement

I wish to acknowledge my supervisors and the external reviewer allowing me to work on this

thesis. I would like to express my very great appreciation to Ursula Siebert for giving me the

opportunity to focus on this highly interesting topic and her continuous trust and support.

I am particularly grateful for the assistance given by the entire ITAW-crew in Büsum, who are

creating a family-like atmosphere. As very important representatives of this second family. I

would like to thank Bianca Unger, Abbo van Neer and Dominik Nachtsheim for inspiring

discussions, calming down and sharing excitement in changing roles. But also to Susanne

Carstens-Michaelis for keeping the team together.

I am especially grateful for my bioacoustics group with the best colleagues to imagine, who

always supported me without any doubts. Johannes Baltzer, you are my most favourite

roommate and I really appreciated your calm manner, lending both ears and providing

distraction or attention, when critically needed. Thank you Fiete, you are a great mentor and

taught me countless theoretical and practical things for experiments and life. My deepest

appreciations goes to my second mentor Joseph Schnitzler who pushed me a lot and taught me

so much about efficiency and the importance of broaden one’s mind. You both shaped the

scientist I am today.

I would like to express my greatest appreciation to my whole family: Mom, Dad, Gerrit and

Marvin, thank you for your continuous support and trust. You were always there for me and

supported every step I made. I hope I can give things back to my parents and will be some day

half a good role model as they were for me.

I owe my deepest gratitude to my lovely wife Claudia. All your love and trust was the most

important support of all. You made it possible that I could do this all. Thanks for your patience

and understanding. You took care that I could live in my bubble while you managed

overwhelming projects and simultaneously took care that I left the bubble from time to time to

breathe. Thank you for all the long evenings and weekends with experiments, in which you

were multiple exposed to my obstacles of the thesis with varying sound exposure levels. You

never left the experiments and always had my back.

A last thank goes to my kind logarithms, you are true friends.

Declaration of Originality

136

Declaration of Originality

I hereby declare that this dissertation, entitled “Effect of anthropogenic underwater noise on

harbour porpoise hearing in areas of high ecological importance” is my own original work.

Further, I have acknowledged all sources used and have cited these in the reference section.

No additional help from third parties was used for preparing this thesis.

Neither did I consult any services, such as consulting agencies, for completing this thesis nor

did anybody receive direct or indirect payment for carrying out any tasks related to this thesis.

The dissertation was drawn up in the following institution:

Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine


The dissertation has not been submitted previously to any institution for assessment purposes.

I hereby confirm that, to the best of my knowledge, all the above and attached declarations are

complete and correct.

………………………………………………………………………………

Date, Signature

Curriculum vitae

137

Curriculum vitae

Personal Details

Name: Tobias Schaffeld

Birthday: 20.01.1987

Birthplace: Kamp-Lintfort

Nationality: German

University Education

2011 – 2016: Master of Science

Wildlife Ecology and Wildlife Management

University of Natural Resources and Life Sciences

Vienna, Austria

Thesis title: “Reduction of accidental bycatches in set-net

fisheries by the use of acoustic signals”

Final grade: 2.0

2007 – 2011 Bachelor of Science

Biology

Heinrich-Heine University,

Düsseldorf, Germany

Thesis title: “Analysis of the foraging behavior of harbour

porpoises (Phocoena phocoena) in selected areas of the Baltic

Sea by static-passive-acoustic monitoring”

Final grade: 2.4

School Education

1997 – 2006: Abitur (A-levels, higher education entrance qualification)

Amplonius-Gymnasium, Rheinberg

1993 – 1997: Primary school

Gemeinschaftsgrundschule Millingen, Rheinberg

Curriculum vitae

138

Work experience

Since 2017 Doctoral candidate



Since 2016 Research associate in different projects of external funds



2015 – 2016 Student research assistant in different projects of external funds



2012 – 2014 Student research assistant in project “Testing new acoustic

harbour porpoise anti-bycatch devices in the German set-net

fisheries.

Von Thünen Institute of Baltic Sea Fisheries

Rostock, Germany

2011 – 2012 Student research assistant in different projects of external funds

German Oceanographic Museum

Stralsund, Germany

2010 Student research assistant, tutor in the course „Biology for

physicians”

Heinrich-Heine University

Düsseldorf, Germany

Scholarships

Grant of the “Gesellschaft der Freunde der TiHo“ for giving a talk and presenting a poster

entitled: “Effects of multiple exposures to pile driving noise on harbour porpoise hearing

during simulated flights a risk evaluation tool” at the „Effects of Noise on Aquatic Life”

conference from 07.-12.07.2019 in the Hague, Netherlands.

Grant for presenting a poster entitled: “Living on the bright side – Harbour porpoises don’t like

rain” and attending the “BioAcoustic Summer School (SeaBASS)” from 5.-10.06.2016 in

Syracuse, USA.

Curriculum vitae

139

Publications

Schaffeld, T., Schnitzler, J. G., Ruser, A., Woelfing, B., Baltzer, J., and Siebert, U. (2020).

“Effects of multiple exposures to pile driving noise on harbor porpoise hearing during

simulated flights—An evaluation tool,” J. Acoust. Soc. Am., 147, 685–697.

doi:10.1121/10.0000595

Schaffeld, T., Ruser, A., Woelfing, B., Baltzer, J., Kristensen, J. H., Larsson, J., Schnitzler, J.

G., Siebert, U. (2019). “The use of seal scarers as a protective mitigation measure can

induce hearing impairment in harbour porpoises,” J. Acoust. Soc. Am., 146, 4288–4298.

Zein, B., Woelfing, B., Dähne, M., Schaffeld, T., Ludwig, S., Rye, J. H., Baltzer, J., Ruser,

A., Siebert, U. (2019). “Time and tide: Seasonal, diel and tidal rhythms in Wadden Sea

Harbour porpoises (Phocoena phocoena),” (S. Li, Ed.) PLoS One, 14, e0213348.


Schnitzler, J. G., Pinzone, M., Autenrieth, M., van Neer, A., IJsseldijk, L. L., Barber, J. L.,

Deaville, R., Jepson, P., Brownlow, A., Schaffeld, T., Thomé, J.P., Tiedemann, R., Das,

K. (2018). “Inter-individual differences in contamination profiles as tracer of social

group association in stranded sperm whales,” Sci. Rep., 8, 10958. doi:10.1038/s41598-

018-29186-z

Schnitzler, J. G., Frédérich, B., Früchtnicht, S., Schaffeld, T., Baltzer, J., Ruser, A., and

Siebert, U. (2017). “Size and shape variations of the bony components of sperm whale

cochleae,” Sci. Rep., 7, 46734. doi:10.1038/srep46734

Schaffeld, T., Bräger, S., Gallus, A., Dähne, M., Krügel, K., Herrmann, A., Jabbusch, M.,

Ruf, T., Verfuß, U.K., Benke, H., Koblitz, J.C. (2016). “Diel and seasonal patterns in

acoustic presence and foraging behaviour of free-ranging harbour porpoises,” Mar. Ecol.

Prog. Ser., 547, 257–272. doi:10.3354/meps11627

Documents

Effects of anthropogenic underwater noise on harbour