Sam Johnston & Kevin Kumagai

HTI Hydroacoustic Technology, Inc. (206) 633-3383 sjohnston@HTIsonar.com

AbstractLow salmon smolt survival continues to be a problem in the Sacramento River Delta despite

efforts to reverse these trends. Predation has been identified as one of the causes of this

decline. Acoustic telemetry is commonly used to track the downstream migration of juvenile

salmonids and has recently been used to identify predatory behavior in other species.

Over the past decade, fine-scale fish tracks have illustrated migration behavior and survival in

river systems throughout California and elsewhere around the world. In recent years as more

data has become available from various species via fine-scale 2D and 3D telemetry, new

questions have emerged. One of the principal questions of great importance in the Bay-Delta

region is: Can we determine whether or not an acoustically-tagged fish has been eaten by a

predator? A critical assumption of survival estimation for acoustically tagged migrating

species is that the detected tag signals are from distinctly unconsumed and freely migrating

fish. Protocols for determining predatory-like movement has been objectively defined for use

in analyzing telemetry data.

In this presentation, we will discuss fine-scale acoustic tag development, current methods for

determining predation events. Fish tracks are presented as two-dimensional fish densities

superimposed over GPS geo-referenced river environments. Various results will be

presented including recent examples of predatory behaviors [e.g., tagged predatory species]

and a review of recent advances in data analysis techniques.

Predator and Chinook Smolt BehaviorFigures 1 and 2 are examples of predatory fish and chinook smolt behavior from 2012

Georgiana Slough study – see CDWR 2012 for study overview and methods .

Predation EventSound pulses from acoustic tags easily pass through a fishes body wall, even if a smaller

fish is consumed by a larger fish. To correctly interpret acoustic tag data it is important to

recognize when a predation event has occurred, in order to correctly classify a tagged fish

for survival studies. If the acoustic tags have short, precisely controlled transmission

intervals, detection and ID ranges that are the same, and are detected on multiple

hydrophones at once, then accurate tracks of individual fish can be generated (Ehrenberg

and Steig 2009). Two tagged smolts whose tracks overlap in space and time (appear to

swim together) may indicate that a predator has consumed two tagged smolts. Another

possibility is that the tagged smolts are exhibiting schooling behavior. Figure 4 shows an

example of a likely predation event because 1) the two tags have continuously overlapping

tracks for over three days, and 2) one of the tags became completely stationary

(defecated) within the array, and remained stationary until the end of the tag battery life.

SummarySimple hydrophone detection data can indicate a predation event has occurred when a tag is

shed (defecated) within detection range (including single hydrophone deployments). If fine

scale 2D or 3D track data is available, then sudden behavioral changes or characteristic,

quantifiable behavioral patterns can be used to infer predation events. Many quantifiable

behavioral characteristics are likely to provide separation between migrating smolt behavior

and predator/consumed smolt behavior. Behavioral characteristics should always be taken in

context, i.e. calculated with reference to concurrent environmental conditions.

All data courtesy of California Department of Water Resources.

References:

CDWR 2012. 2011 Georgiana Slough Non-Physical Barrier Performance Evaluation Project

Report (final), prepared by AECOM for California Department of Water Resources, September

5, 2012, 228 pp.

Ehrenberg, J. E., and Steig, T. W. 2009. A study of the relationship between tag-signal

characteristics and achievable performances in acoustic fish-tag studies. – ICES Journal of

Marine Science, 66: 1278–1283.

Vogel, D.A. 2010. Evaluation of acoustic –tagged juvenile chinook salmon and predatory fish

movements in the Sacramento – San Joaquin Delta during the 2010 Vernalis Adaptive

Management Program. Natural Resource Scientists, Inc. October, 2010. 73 p.

Smolt/Predator Behavior DifferencesUnderstanding Predator behavior – and distinguishing it from migrating smolt behavior – is

key to correctly interpreting acoustic tag results (Vogel 2010). Using two dimensional and

three dimensional tracking, behavioral characteristics of tagged fish can be quantified and

compared. However, behavior results should be interpreted in context with concurrent

environmental factors. Figure 6 shows a comparison of two behavior characteristics, (simple

sinuosity and average speed over ground) for known tagged predators, tagged smolts, tagged

smolts that are suspected to have been eaten, and shed tags during periods of a) high tide

(low water velocity) and b) low tide (high water velocity).

Steps Toward Evaluating Predation

in the Sacramento River Delta7th Biennial

Bay-Delta Science Conference

October 16-18, 2012

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Figure 1. Tracks of acoustically tagged predatory fish, Georgiana Slough, Spring,

2012.

Smallmouth bass (tag code 2028.15, green spheres) and Sacramento pikeminnow (tag code 2070.15, pink

spheres) were margin oriented while striped bass (tag codes 2154.15 and 2910.15, blue and yellow spheres)

associated with the open water. Data courtesy of CDWR.

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Striped Bass(Morone saxatilis)

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Figure 3. ‘Radar’ plots of movement of predatory fish and salmon smolts.

The complete track of each fish in Figures1 and 2 was broken up into line segments of approximately 10

seconds in duration. The direction of travel of each segment was then calculated and summarized in the

above plots – 0 degrees is True North.

Figure 4. Two simultaneous tags.

Two chinook tags (2364.25, red spheres, and 3690.19, blue spheres) enter array individually from upstream.

Tags begin swimming simultaneously at 3:19:40 on March 26 continuing for three plus days. Tag 3960.19

defecated at 7:45:51 on March 29. Tag 2364.25 leaves array back upstream. Data courtesy of CDWR

Figure 5. Tag defecated within hydrophone array.

Raw detection data from Tag 3690.19, originally implanted into a chinook smolt ,spans 5 hours from 05:00 to

10:00. The tag suddenly stops all movement within the hydrophone array at Georgiana Slough on March

29, 7:45:51. Each colored line represents data from one individual hydrophone.

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Mean Speed Over Ground vs Sinuosity for All Tracks

During Hour 06:00, March 27, 2012 (High Tide, Low Water Velocity)

Tagged Smolts

Tagged Predators

Predation Smolts

Stationary Tags

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During Hour 14:00, March 27, 2012 (Low Tide, High Water Velocity)

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Figure 6. Tag movement characteristics under different water velocity conditions.

Behavior parameters sinuosity and average speed over ground (SOG) of known tagged predators, tagged

smolts, and smolts suspected of having been consumed by predators are compared for different water

velocity conditions. While average SOG for tagged smolts increased during higher water velocity, predator

SOG values remained similar.

a) b)

Figure 2. Tracks of acoustically tagged chinook salmon smolts, Georgiana

Slough, Spring, 2012.

Chinook tags (tag codes 3939.19 and 2742.12, turquoise and lime spheres, respectively) travel down the

Sacramento River while (tag codes 2532.25 and 2175.28, orange and lavender spheres, respectively) move

down Georgiana Slough. Data courtesy of CDWR.

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Chinook Salmon Smolt

( Oncorhynchus tshawytscha)Tag 3939.19

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Chinook Salmon Smolt

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Chinook Salmon Smolt

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Chinook Salmon Smolt

( Oncorhynchus tshawytscha)Tag 2175_28