Andrew Schultz USBR, Kevin Kumagai HTI U.S. Bureau of Reclamation, Tracy Fish Collection Facility, Byron, CA. In the Sacramento‐San Joaquin Delta, several salmonid species are listed as threatened or endangered. One potential cause of lower juvenile salmonid survival may be striped bass predation. Acoustic tags are routinely used to estimate survival by releasing and detecting tagged juvenile salmonids with the assumption that tagged salmonids are not consumed by other fishes. If this assumption is violated, salmonid survival estimates may be misinterpreted. A key consideration is the time taken by an acoustic tag to pass through the digestive tract of a predatory fish. To measure evacuation rates, acoustically tagged juvenile Chinook salmon were euthanized, then tethered and fed to free swimming (acoustically tagged and wild) striped bass in the primary channel of the Tracy Fish Collection Facility. Confirmation of time at predation event was determined by analysis of 2D acoustics tracks. The amount of time required for an acoustic tag to pass through the digestive tract of a striped bass estimated the evacuation rate. Mean tag evacuation time was 1.8 d (n = 14; SD = 0.49; range = 1.2 to 2.7). Mean tagged salmon was 146.6 mm FL (n = 14; SD = 7.6; range = 131 to 165). Results indicated free swimming striped bass evacuate small acoustic tags (0.5 g) relatively quickly in 22°C water. By comparison, a study investigating predation events using larger tags (1.1 g) on relatively sedentary laboratory fish held in 16°C had greater evacuation times. This feasibility study demonstrated acoustic tags can provide information about predation and gut evacuation in free‐swimming predatory fish. As a result, the Bureau of Reclamation extended testing of predation and gut evacuation rates to include temperature variation and food availability levels in the Tracy Fish Collection Facility Primary Channel, starting late 2013.

1. Predation and Gut Evacuation Rates
as Measured by Acoustic Tags in the
Tracy Fish Collection Facility Primary Channel
Andrew Schultz, PhD (Reclamation) and Kevin Kumagai (HTI)

2. Overview
• Sacramento-San Joaquin Delta - several salmonid
species are listed as threatened or endangered
• Acoustic telemetry - powerful tool to study movement
and survival of juvenile salmonids
• Predation may lower salmonid survival and confounds
ability to adequately assess acoustic data
• Evacuation rate or time taken by an acoustic tag to pass
through the digestive tract of a predatory fish is largely
unknown

3. Objective
• Proof of concept experiment to determine the rate free
swimming predatory fish digestively pass acoustic tags
that were implanted in Chinook salmon

4. Methods
• Tags (0.5 g) removed from recaptured fish used in the Tracy Loss
Study (Karp et al, In prep)

5. Methods
• Tags reprogrammed for this proof of concept experiment
(Kumagai, In prep)

6. Methods
• Deployed acoustically-tagged dead chinook salmon via a binder clip
and a fishing pole (n=14) (Schultz et al, In prep)

7. Methods
• Acoustically-tagged striped bass in primary channel as part of the
Tracy Loss Study (n = 7) (Karp et al, In prep)

8. Methods
• Verified predation time via 2-dimensional tracks and detection signal
DEPLOYED
Tagged salmon
separate from
striped bass
(6/21/13 10:20)
CONSUMED
Simultaneous tag
tracks in striped bass
and salmon
(6/21/13 10:20-10:25)

9. Methods
• Verified tag evacuation time via 2-dimensional tracks and detection signal
IN GUT
Simultaneous tag
tracks in striped bass
and salmon continues
for almost 2 days
(6/23/13 9:10-9:15)
EVACUATED
Moving as two
separate tags after
(6/23/13 9:15:39)

10. Verified tag evacuation times via detection signal patterns:
single hydrophone (Kumagai, In Prep)
IN GUT EVACUATED
Methods

11. Verified tag defecation times via detection signal patterns:
multiple hydrophones (Kumagai, In prep)
IN GUT EVACUATED
Methods

12. Results
• Mean tag evacuation time was 1.8 days
(n = 14, SD = 0.49, range = 1.2 to 2.7)
• Mean FL of tagged salmon was 146.6 mm
(n = 14, SD = 7.6, range = 131 to 165)

13. Salmon Length vs Days to Tag Evacuation
130
140
150
160
170
1 2 3
ForkLength(mm)
Days to Tag Evacuation

14. Tagged striped bass (2897.18) was 2.53 kg and 588 mm FL
when released on 5/2/2013
2 days (average) to evacuate
tag within 157 mm FL salmon

15. Tagged striped bass (2729.18) was 1.59 kg and 505 mm FL
when released on 5/3/2013
1.4 days to evacuate tag
within 145 mm FL salmon

16. Same defecation time but consumed 32 minutes apart
2.7 days (average) to evacuate
tag within 142 mm salmon

17. Mean tag evacuation time was 1.8 days.
Mean tagged salmon was 147 mm FL.

18. Summary / Discussion
• Mean tag evacuation time was 1.8 days (n = 14, SD = 0.49, range
= 1.2 to 2.7) across a naturally variable water temperature ranging
from 23 to 26oC during the study.
• Evacuation times for this study appear much shorter than times for
predation tags (1.1 g) in relatively sedentary laboratory fish held in
16oC water (Schultz et al, in prep)
• High confidence in ability to confirm predation and measure the
rate at which free swimming predatory fish digestively pass
acoustic tags that were implanted in Chinook salmon
• As a result of this proof of concept experiment, the Bureau of
Reclamation is collecting similar data in the primary channel at
different temperature and food availability levels

19. References
• Ehrenberg, J. E. and T.W. Steig. 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.
• Karp, C., A.A. Schultz, B. Wu, and J. Israel. In prep. Evaluation of
Chinook Salmon and Central Valley Steelhead Facility Losses at the
Tracy Fish Collection Facility. Bureau Of Reclamation.
• Kumagai, K.K. In prep. Acoustic tag detections and tracking of fish
predation and acoustic tag defecation at the Tracy Fish Collection
Facility in 2013. Report to Bureau of Reclamation, Byron, Calif., by
Hydroacoustic Technology, Inc., Seattle, Wash.
• Schultz, A.A., V.B. Afentoulis, K.W. Clark, and B.B. Bridges. In prep.
Evacuation Rates of Acoustic Tags in Striped Bass. Bureau of
Reclamation.

20. Acknowledgments
• Reclamation
Brent Bridges, Cathy Karp, Scott Porter, Rene
Reyes, Mike Trask, Brandon Wu
• CA–DWR
Virginia Afentoulis and Kevin Clark
• HTI
Sam Johnston and Colleen Sullivan

21. Questions

22. Removal of fish from the nets (BOR, unpublished data)

23. Striped bass, 6/21/13 10:05-10:10
Tagged striped bass (red spheres) in primary channel. Data courtesy of
BOR.

24. Striped bass, 6/21/13 10:10-10:15
Tagged striped bass (red spheres) in primary channel. Data courtesy of
BOR.

25. Predation, 6/21/13 10:15-10:20
Tagged striped bass (red spheres) consumes dead chinook (blue
spheres) approximately 6/21/13 10:20. Data courtesy of BOR.

26. Simultaneous tags, 6/21/13 10:20-10:25
Two tags are simultaneous for almost two days. Data courtesy of BOR.

27. Simultaneous tags continues for almost two
days, 6/23/13 9:10-9:15
Simultaneous tags together for almost two days. Data courtesy of BOR.

28. Tag defecation, 9:15-9:20
Chinook tag (blue spheres) defecated approximately 6/23/13 9:15:39.
Data courtesy of BOR.

29. Separate tags, 9:20-9:25
Striped bass continues moving around primary channel while chinook
tag stationary. Data courtesy of BOR.

30. Separate tags, 9:25-9:30
Striped bass moving around primary channel while chinook tag
stationary. Data courtesy of BOR.

31. Separate tags, 9:30-9:35
Striped bass continues moving around primary channel while chinook
tag stationary. Data courtesy of BOR.

32. Separate tags, 9:35-9:40
Striped bass continues moving around primary channel while chinook
tag stationary. Data courtesy of BOR.

33. Separate tags, 9:40-9:45
Striped bass continues moving around primary channel while chinook
tag stationary. Data courtesy of BOR.

34. Predation and simultaneous tags summary
Downstream
Upstream
Barrier
Time Slider
Steelhead 2D positions(green)
Striped bass 2D positions(red)
Sun and moon gadget
Tagged striped bass (red spheres) consumed tagged dead chinook (blue
spheres) and the two tags swim simultaneouly for almost two days. Data
courtesy of BOR.

35. Defecation Summary
Data courtesy of BOR.

36. Single hydrophone: tag defecation
Time duration 1 hour

37. Multiple hydrophones: tag defecation
Time duration 1 hour