Steps Toward Evaluating Fish Predation in the Sacramento River Delta
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Steps Toward Evaluating Fish Predation in the Sacramento River Delta

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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 decline.......

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 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. 

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  • 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 AbstractLow salmon smolt survival continues to be a problem in the Sacramento River Delta despiteefforts 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 2070.15salmonids and has recently been used to identify predatory behavior in other species. 340350 4000 0 10 20 0 340 350 80 0 10 20 330 30 0 340350 80 10 20 330 70 30 320 3500 40 340350 450 10 20 330 70 30 320 60 40 3000 330 400 30 320 40 310 50Over the past decade, fine-scale fish tracks have illustrated migration behavior and survival in 300 310 2500 2000 50 60 320 310 350 300 40 50 300 310 60 50 50 60 300 50 40 60 250 40 30river systems throughout California and elsewhere around the world. In recent years as more 290 280 1500 1000 70 80 300 290 200 150 60 70 290 30 20 70 290 280 20 70 80 500 280 80 10data has become available from various species via fine-scale 2D and 3D telemetry, new 270 0 90 280 270 100 50 0 80 90 270 10 0 90 270 0 90 260 100 260 100questions have emerged. One of the principal questions of great importance in the Bay-Delta 250 110 260 100 260 250 100 110 250 110 250 110 240 120region is: Can we determine whether or not an acoustically-tagged fish has been eaten by a 240 230 120 130 240 120 240 230 120 130 230 130 220 140 230 130 220 140predator? A critical assumption of survival estimation for acoustically tagged migrating 210 200190 170160 150 220 210 140 150 220 210 200190 150 140 210 200 190 170 160 150 180 200190 170160 170160 180species is that the detected tag signals are from distinctly unconsumed and freely migrating 180 180fish. Protocols for determining predatory-like movement has been objectively defined for usein 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 todetermining 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 Marchsuperimposed 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. 0 0 0 0presented including recent examples of predatory behaviors [e.g., tagged predatory species] 330 340 350 25 10 20 30 330 340 350 18 16 10 20 30 330 340350 25 10 20 30 330 340 350 30 10 20 30 320 20 40 320 25 40 320 20 40and a review of recent advances in data analysis techniques. 320 14 40 300 290 310 15 10 50 60 70 300 290 310 12 10 8 6 50 60 70 300 290 310 15 10 50 60 70 290 310 300 20 15 10 50 60 70 Smolt/Predator Behavior Differences 280 5 80 280 4 80 280 5 80 280 5 80Predator and Chinook Smolt Behavior 270 260 250 0 90 100 110 270 260 250 2 0 90 100 110 270 260 250 0 90 100 110 270 260 250 0 110 90 100 Understanding Predator behavior – and distinguishing it from migrating smolt behavior – is key to correctly interpreting acoustic tag results (Vogel 2010). Using two dimensional andFigures 1 and 2 are examples of predatory fish and chinook smolt behavior from 2012 240 120 240 120 240 230 120 130 240 120 three dimensional tracking, behavioral characteristics of tagged fish can be quantified and 230 130Georgiana Slough study – see CDWR 2012 for study overview and methods . 230 130 230 130 220 140 220 140 220 140 220 140 210 200 190 170 160 150 210 200 190 170 160 150 210 200190 170160 150 210 200 190 170 160 150 compared. However, behavior results should be interpreted in context with concurrent 180 180 180 180 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) 40 40 Predation Event 35 35 30 30 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 10 Stationary Tags 1 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.