This document discusses using acoustic telemetry to study predation on juvenile salmonids in the Sacramento River Delta. Fine-scale fish tracking data can identify predatory behaviors and potential predation events. Predators exhibit margin-oriented movement while salmon smolts travel through open water. Overlapping tracks or tags becoming stationary may indicate predation. Behavioral metrics like sinuosity and speed distinguish predators from migrating salmon under different water velocity conditions. Quantifying fish behaviors aids understanding predation impacts on salmon survival in the Delta.

1. Steps Toward Evaluating Predation
in the Sacramento River Delta 7th Biennial
Sam Johnston & Kevin Kumagai
Bay-Delta Science Conference
HTI Hydroacoustic Technology, Inc. (206) 633-3383 sjohnston@HTIsonar.com
October 16-18, 2012
Abstract
Low 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 Smallmouth Bass Sacramento Striped Bass Striped Bass
Pikeminnow (Morone saxatilis) (Morone saxatilis)
(Micropterus dolomieu)
decline. Acoustic telemetry is commonly used to track the downstream migration of juvenile 2028.15 (Ptychocheilus grandis) 2154.15
2910.15
Tag 2070.15
salmonids and has recently been used to identify predatory behavior in other species. 340350
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river systems throughout California and elsewhere around the world. In recent years as more 290
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questions have emerged. One of the principal questions of great importance in the Bay-Delta 250 110
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region is: Can we determine whether or not an acoustically-tagged fish has been eaten by a 240
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predator? A critical assumption of survival estimation for acoustically tagged migrating 210
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species is that the detected tag signals are from distinctly unconsumed and freely migrating 180 180
fish. Protocols for determining predatory-like movement has been objectively defined for use
in analyzing telemetry data.
Figure 5. Tag defecated within hydrophone array.
In this presentation, we will discuss fine-scale acoustic tag development, current methods for Chinook Salmon Chinook Salmon Chinook Salmon Chinook Salmon Raw detection data from Tag 3690.19, originally implanted into a chinook smolt ,spans 5 hours from 05:00 to
determining predation events. Fish tracks are presented as two-dimensional fish densities Smolt Smolt Smolt Smolt
( Oncorhynchus tshawytscha) ( Oncorhynchus tshawytscha) ( Oncorhynchus tshawytscha) ( Oncorhynchus tshawytscha) 10:00. The tag suddenly stops all movement within the hydrophone array at Georgiana Slough on March
superimposed over GPS geo-referenced river environments. Various results will be Tag 3939.19 Tag 2742.12 Tag 2532.25 Tag 2175_28
29, 7:45:51. Each colored line represents data from one individual hydrophone.
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Smolt/Predator Behavior Differences
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Understanding Predator behavior – and distinguishing it from migrating smolt behavior – is
key to correctly interpreting acoustic tag results (Vogel 2010). Using two dimensional and
Figures 1 and 2 are examples of predatory fish and chinook smolt behavior from 2012 240 120 240 120 240
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three dimensional tracking, behavioral characteristics of tagged fish can be quantified and
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Georgiana Slough study – see CDWR 2012 for study overview and methods .
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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).
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 Mean Speed Over Ground vs Sinuosity for Mean Speed Over Ground vs Sinuosity for
above plots – 0 degrees is True North. All Tracks All Tracks
During Hour 06:00, March 27, 2012 (High During Hour 14:00, March 27, 2012 (Low
Tide, Low Water Velocity) Tide, High Water Velocity)
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Predation Event 35 35
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Sound pulses from acoustic tags easily pass through a fishes body wall, even if a smaller 25 25
fish is consumed by a larger fish. To correctly interpret acoustic tag data it is important to
Sinuosity
Sinuosity
20 Tagged Smolts 20 Tagged Smolts
recognize when a predation event has occurred, in order to correctly classify a tagged fish a) Tagged Predators b) Tagged Predators
15 Predation Smolts 15 Predation Smolts
for survival studies. If the acoustic tags have short, precisely controlled transmission 10
Stationary Tags
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Stationary Tags
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intervals, detection and ID ranges that are the same, and are detected on multiple 5 5
hydrophones at once, then accurate tracks of individual fish can be generated (Ehrenberg 0 0
and Steig 2009). Two tagged smolts whose tracks overlap in space and time (appear to 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Mean Speed Over Ground (m/s) Mean Speed Over Ground (m/s)
swim together) may indicate that a predator has consumed two tagged smolts. Another
Figure 1. Tracks of acoustically tagged predatory fish, Georgiana Slough, Spring, possibility is that the tagged smolts are exhibiting schooling behavior. Figure 4 shows an Figure 6. Tag movement characteristics under different water velocity conditions.
2012. example of a likely predation event because 1) the two tags have continuously overlapping Behavior parameters sinuosity and average speed over ground (SOG) of known tagged predators, tagged
Smallmouth bass (tag code 2028.15, green spheres) and Sacramento pikeminnow (tag code 2070.15, pink tracks for over three days, and 2) one of the tags became completely stationary smolts, and smolts suspected of having been consumed by predators are compared for different water
spheres) were margin oriented while striped bass (tag codes 2154.15 and 2910.15, blue and yellow spheres) (defecated) within the array, and remained stationary until the end of the tag battery life. velocity conditions. While average SOG for tagged smolts increased during higher water velocity, predator
associated with the open water. Data courtesy of CDWR. SOG values remained similar.
Summary
Simple 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
Figure 4. Two simultaneous tags. Marine Science, 66: 1278–1283.
Figure 2. Tracks of acoustically tagged chinook salmon smolts, Georgiana Two chinook tags (2364.25, red spheres, and 3690.19, blue spheres) enter array individually from upstream.
Slough, Spring, 2012. Tags begin swimming simultaneously at 3:19:40 on March 26 continuing for three plus days. Tag 3960.19 Vogel, D.A. 2010. Evaluation of acoustic –tagged juvenile chinook salmon and predatory fish
Chinook tags (tag codes 3939.19 and 2742.12, turquoise and lime spheres, respectively) travel down the defecated at 7:45:51 on March 29. Tag 2364.25 leaves array back upstream. Data courtesy of CDWR movements in the Sacramento – San Joaquin Delta during the 2010 Vernalis Adaptive
Sacramento River while (tag codes 2532.25 and 2175.28, orange and lavender spheres, respectively) move Management Program. Natural Resource Scientists, Inc. October, 2010. 73 p.
down Georgiana Slough. Data courtesy of CDWR.