Dredging Sounds: Potential Impacts on Aquatic Organisms
Dr. Douglas Clarke
HDR Engineering Vicksburg, Mississippi
USA
Topics
Background Dredging scenarios and risk management Hearing capabilities of organisms of
concern Potential responses of receptor organisms Challenges in assessing dredging impacts Knowledge gaps relevant to dredging Conclusions
Background
St. Joseph Harbor, MI, USA
Do fishes (etc.) respond to the presence of a dredge? Is sound the stimulus they are responding to?
Increasing Distance from Dredge DREDGE LOCATION
30 m
RISK FRAMEWORK
Problem Formulation
Exposure Assessment
Effects Assessment
Risk Characterization
Risk Management
RISK ASSESSMENT PARADIGM Economic Analysis,
Socio-Political, Engineering Feasibility
Risk = f (Exposure + Effect)
Management Practices
Dredging Scenarios
• Shallow water channels and harbors (< 20 m) • primarily cutterhead and grab dredgers • complex bathymetry and hydrodynamics • high suspended sediment regime, fine sediments • “noisy” ambient soundscape
• Inshore shelf and coastal inlets (< 50 m) • primarily trailer suction hopper dredges and cutterhead dredges • simple bathymetry • low ambient suspended sediment regime, coarse sediments
• Deep water (> 50 m) – large pumping capacity trailer suction hopper dredges • relatively quiet oceanic ambient soundscape
EFFECTS OF HUMAN-MADE SOUND
BEHAVIORAL RESPONSES
MASKING
TEMPORARY THRESHOLD SHIFT
NO
ISE
SO
UR
CE
L
EV
EL
Q
UIE
T
LO
UD
PHYSIOLOGICAL EFFECT
MORTALITY
DISTANCE FROM NOISE SOURCE From Popper 2011
Sound Inaudible
Hearing Capabilities of Aquatic Organisms
Aquatic organisms can be sensitive to sound pressure and/or particle motion
Audiograms define the lowest level of sound that can be perceived by a given species as a function of frequency
Audiograms can be measured using behavioral or electrophysiological methods
Auditory Evoked Potential (AEP) Auditory Brainstem Response (ABR)
From Martin et al. (2012)
Loggerhead Sea Turtle Audiograms
Dredge Sounds
Fish Audiograms
Audiograms of several fish species that are sensitive primarily to particle motion
Dredge Sounds
From Popper et al. (2014)
Fish Audiograms
Audiograms of several fish species that are sensitive primarily to sound pressure
Dredge Sounds From Popper et al. (2014)
Marine Mammal Audiograms
From Erbe (2014)
Dredge Sounds
Key References
Popper et al. (2014) Sound Exposure Guidelines for Fishes and Sea Turtles.
Southall et al. (2007) Marine Mammal Exposure Criteria: Initial Scientic
Recommendations.
Risk-Based Effects Criteria for Marine Mammal Exposures to Continuous Sounds
Marine Mammal Group
Metric
Sound Type Single Pulse Multiple Pulses Non Pulses
Low-Frequency Cetaceans
SPL1 230 230 230 SEL2 198 198 215
Mid-Frequency Cetaceans
SPL 230 230 230 SEL 198 198 215
High-Frequency Cetaceans
SPL 230 230 230 SEL 198 198 215
Pinnipeds in Water
SPL 218 218 218 SEL 186 186 203
Based on Southall et al. (2007)
1 SPL in dB re:1uPa (peak)(flat), 2 SEL in dB re:1uPa2-s (M) Note: Values estimated to cause PTS onset, TTS onset generally 20 dB lower
Risk-Based Effects Criteria for Fish Exposed to Continuous Sounds
Animal Type
Field
Potential Mortality
Impairment Behavior
Recoverable Injury
TTS
Masking
Fish without swimbladder
N Low Low Moderate High Moderate I Low Low Low High Moderate F Low Low Low Moderate Low
Fish with swimbladder not involved in hearing
N Low Low Moderate High Moderate I Low Low Low High Moderate F Low Low Low Moderate Low
Fish with swimbladder involved in hearing
N Low 170 dB rms 158 dB rms High High I Low For For High Moderate F Low 48 hrs 12 hrs High Low
Eggs and Larvae
N Low Low Moderate High Moderate I Low Low Low Moderate Moderate F Low Low Low Low Low
Based on Popper et al. (2014) Near Interm. Far-Field
Risk-Based Effects Criteria for Sea Turtles Exposed to Continuous Sounds
Animal Type
Field
Potential Mortality
Impairment Behavior Recoverable
Injury
TTS
Masking Sea
Turtles N Low Low Moderate High Moderate I Low Low Low Moderate Moderate F Low Low Low Low Low
Based on Popper et al. (2014)
There are “no data on exposure or received levels that enable guideline numbers to be provided.” Note: No comparable effects criteria are available for invertebrates.
N = Near Field, I = Intermediate Field, F = Far Field
“Very little research has been carried out on the effects of sound from dredging on fishes and aquatic invertebrates. In general the effects will be chronic rather than acute. Behavioral responses and masking are to be expected, with possible negative consequences.”
A.D. Hawkins, A. E. Pembroke, and A.N. Popper. 2015. Information gaps in understanding the effects of noise on fishes and invertebrates. Reviews in Fish Biology and Fisheries 25:39-64
The Good News
The Good News
• A consensus is emerging that dredges do not pose a threat of acute impacts.
• Dredges do not produce sufficiently intense sound pressure levels to induce PTS or tissue damage in fishes, and probably not in invertebrates.
• The majority of fish species perceive particle motion rather than the pressure component of sound, and particle motion attenuates much more rapidly than pressure. Therefore TTS and behavioral impacts on fishes should occur only for exposures in the near field.
“Very little research has been carried out on the effects of sound from dredging on fishes and aquatic invertebrates. In general the effects will be chronic rather than acute. Behavioral responses and masking are to be expected, with possible negative consequences.”
A.D. Hawkins, A. E. Pembroke, and A.N. Popper. 2015. Information gaps in understanding the effects of noise on fishes and invertebrates. Reviews in Fish Biology and Fisheries 25:39-64
The Bad News
The Bad News
• Measuring particle motion is in its infancy. Propagation models capable of predicting attenuation distances of particle motion are not in broad use.
• Sound pressure remains a concern for fishes with adaptions that render them susceptible to behavioral effects (e.g., many migratory species).
• Monitoring the occurrence of TTS, masking and behavioral effects is very difficult.
• Interpretation of the significance of TTS, masking and behavioral effects at the population level is exceedingly difficult.
Species-Specific Considerations
Factors that influence response to sound and other stimuli
life history stage size relative to wavelength of sound anatomical differences location in the water column relative to the source behavioral differences
startle response, habituation attraction or avoidance territorial or transient
Some Examples of TSS, Masking and Behavioral Effects
102
103
104
105
106
0
2
4
6
8
10
12
14
16
18
Frequency (Hz)
Dete
ction
dist
ance
(km
)
102
103
104
105
10670
80
90
100
110
120
130
140
150
160
dB re
1 µ
Pa rm
s
Example Baltic; TSHD TL = 15 log (r) From Thomsen and Schack (2012)
Detection of Dredging Sound D
etec
tion
Dis
tanc
e (k
m)
dB r
e 1
uPa
rms
Frequency (Hz)
Behavioral Responses
Avoidance or attraction to sound source
Altered swimming behavior Access to spawning, nursery or foraging habitat
Habituation
Harbor Porpoise Response to Sand Dredging
Porpoise densities surveyed along aerial transects. Deployment of passive acoustic monitoring devices (T-PODs).
Response limited to 3 hour avoidance of immediate vicinity of the dredger.
From Diederichs et al (2010)
N
BUCKET DREDGE PLUME COMPOSITE SURVEY
DREDGE LOCATION
DREDGE
Barrier to migration?
Habituation
Courtesy of Gerard van Raalte - Boskalis
Masking Effects
Masking may affect prey detection or anti-predator behaviors.
Masking may be particularly important for soniferous fishes (e.g., cods, croakers, groupers). Fishes produce sounds associated with spawning behavior, aggregating behavior, and orientation.
Masking may lead to compensatory responses, such as altered vocalizations.
Masking: Interference with the detection of one sound (signal) by another sound (masker). - Based on Hawkins et al. (2015)
Marine Mammal Vocalizations
From Erbe (2014).
Marine Mammal Vocalizations
From Erbe (2014).
Maasvlakte 2 Monitoring Example
Species PTS Risk Threshold
TTS Risk Threshold
Weighting
Harbor Porpoise
215 195 Mhf
Harbor Seal 203 183 Mpw
Fish < 2g - 187 None
Fish > 2g - 183 None
Based on Heinis et al. (2012)
Maasvlakte 2 Monitoring Example
Species Harbor Porpoise
Harbor Seal Fish < 2g Fish > 2g
TTS threshold SEL
195 dB re:1uPa2-s
183 dB re:1uPa2-s
187 dB re:1uPa2-s
183 dB re:1uPa2-s
Distance from dredge at which TTS threshold is
exceeded
n/a
90 m
100 m
400 m
Based on Heinis et al. (2012)
Note: Animal moving at speed of 1 m/s with respect to the dredge for a total exposure of 24 hrs.
Maasvlakte Monitoring Example
Based on Heinis et al. (2012)
Relationship between distance to dredging vessel and SEL (dB re 1 μPa2s) of a swimming animal with a relative speed with respect to the ship of 1 m/s at a depth of 1 m and 16 m.
Based on Heinis et al. (2012)
TTS for HF cetaceans
SEL
Animal swimming at 1 m/s at a depth of 16 m
Distance from Dredge
TTS for fish > 2 g
TTS for pinnipeds and fish < 2 g
(Exceedance at ~80 m for pinnipeds, ~300 m for fish < 2 g)
(Exceedance at ~100 m)
(No exceedance)
Mechanical Dredges: Worst Case Scenarios?
Grab Dredge Viking Backhoe Dredge New York
Latest Guidance
• Measure both sound pressure and particle motion received by the organism of concern.
• Audiograms should be based on behavioral rather than physiological responses.
• Ideally, responses should be observed for free ranging organisms rather than captive organisms.
Challenges to Assessing Dredging Impacts
• What aspects of continuous sound are most problematic to aquatic organisms?
• What are the appropriate metrics and response characteristics for different taxonomic groups?
• What are the appropriate means (e.g., models) to quantify sound propagation in shallow water?
• How can pressure and particle motion exposures of fishes and invertebrates be measured at different locations in the water column (benthic – pelagic)?
Adapted from Hawkins et al. (2015)
Challenges to Assessing Dredging Impacts
• How can effects of exposure to dredging sounds be distinguished from suspended sediments effects?
• How can effects on behavior be evaluated in terms of risk of biologically meaningful consequences?
• How can masking effects be evaluated in terms of risk of biologically meaningful consequences?
• Is an avoidance response sufficient to minimize impacts, and if so, for how long?
Knowledge Gaps Relevant to Dredging
Incomplete library of dredging process sounds for different dredge types, sizes and scenarios (e.g., substrates)
Place dredging sounds into perspective with ambient sound fields and other natural and anthropogenic sources (e.g., shipping)
Provide theoretical groundwork for assessments of dredging sound impacts on key species
Conclusions • Although scientific evidence indicates that dredging sounds pose
minimal risk to most aquatic organisms, knowledge gaps exist in our ability to assess the biological consequences of masking or behavioral effects.
• Methods are needed to monitor responses of free ranging organisms to dredging-induced sounds, and to apply models to accurately predict exposures.
• Species-specific and site-specific factors determine the need for risk reducting management practices.
• As underwater sound criteria emerge there needs to be effective lines of communication between the dredging industry, regulators, and the scientific community.
References Diederichs, A, Brandt, M & G Nehls (2010) Does sand extraction near Sylt affect harbor porpoises? Wadden Sea Ecosystem No. 26 Erbe, C. (2014) Effects of underwater noise on marine mammals. In Popper & Hawkins (eds), The Effects of Noise on Aquatic Life. Advances in Experimental Medicine and Biology, Springer Hawkins, AD, Roberts, L & S Cheesman (2014) Responses of free-living coastal pelagic fish to impulsive sounds. Journal of the Acoustical Society of America 135(5):3101-3116 Hawkins, AD, Pembroke, AE & AN Popper (2015) Information gaps in understanding the effects of noise on fishes and invertebrates. Reviews in Fish Biology and Fisheries 25:39-64 Heinis, F, de Jong, C, Ainslie, M, Borst, W. and T. Vellinga (2013) Monitoring programme for the Maasvlakte 2, Part III – The effects of underwater sound. Terra et Aqua 132 (Sept) Martin, KJ et al (2012) Underwater hearing in the loggerhead turtle (Caretta caretta): a comparison of behavioral and auditory evoked potential audiograms. Journal of Experimental Biology 215:3001-3005 Popper, AN & Hastings (2009) The effects of anthropogenic sound on fishes. Journal of Fish Biology 75:455-489 Popper, AN et al (2014) Sound Exposure Guidelines for Fishes and Sea Turtles: A Techniical Report Prepared by ANSI-Accredited Standards Committee S3/SC1, Springer Briefs in Oceanography Simpson, SD, Purser, J & AN Radford (2014) Anthropogenic noise compromises behaviour in European eels. Global Change Biology Southall, BL, et al (2007) Marine mammal noise exposure guidelines: initial scientific recommendations. Aquatic Mammology 33:411-521
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