The optimal management of salmonids in the Delta requires that the true fate of each tagged fish be known. Loss of tagged salmonids due to predation has been estimated to be as high as 65% (Vogel 2011). This data is ambiguous at best and survival estimates and behavioral results are biased. Hydroacoustic Technology Incorporated (HTI) has developed a prototype acoustic tag that has the ability to signal when a tagged fish has been eaten by a predatory fish. DWR and USBR staff were given 100 prototype predation tags for efficacy testing in live Chinook salmon.

1. Predation Tag – An Effective Means of Determining if a Striper Ate a Salmon?Virginia Afentoulis, (vafentou@water.ca.gov), Environmental Scientist, CA Dept. of Water Resources (CDWR), Bay Delta Office, Delta Conveyance – Fish Science. Andrew Schultz (aschultz@usbr.gov) Fisheries
Biologist - U.S. Bureau of Reclamation. Curtis Yip (cyip@water.ca.gov), Environmental Scientist, CDWR. Michele (Nikki) Johnson (johnsonm@water.ca.gov) Environmental Scientist, CDWR.
C
We would like to acknowledge the following people for their help on this work:
Kevin Clark, Senior Environmental Scientist, CDWR, Bryce Kozak, Fish and Wildlife Technician, CDWR; Oliver Patton, Fish and Wildlife Scientific Aid, CDWR; Laura Rudolph, Fish and Wildlife Scientific Aid, CDWR, Jamie Suria, Fish and Wildlife Scientific Aid, CDWR; Kevin Kumagai of HTI; Brent Bridges, Scott Porter, Michael Trask and Rene Reyes of the USBR.
Introduction
Methods
Results
Conclusions
The optimal management of salmonids in the Delta requires that the true fate
of each tagged fish be known. Loss of tagged salmonids due to predation
has been estimated to be as high as 65% (Vogel 2011). This data is ambiguous
at best and survival estimates and behavioral results are biased. Hydroacoustic
Technology Incorporated (HTI) has developed a prototype acoustic tag that
has the ability to signal when a tagged fish has been eaten by a predatory fish.
DWR and USBR staff were given 100 prototype predation tags for efficacy
testing in live Chinook salmon (Figure 1).
Experiments were carried out in a laboratory setting (US Bureau of
Reclamation's Tracy Aquaculture Facility, TAF), with a controlled water
supply, maintained at 16oC. Six striped bass (Morone saxatilis) were held in
tanks at the TAF and were each sequentially fed 10 live Chinook salmon
(Oncorhynchus tshawytscha) with implanted prototype predation tags.
In order to monitor the predation tag signal, we placed hydrophones in
each of the six striped bass tanks, which were connected to a HTI ATR 290
(Acoustic Tag Receiver) (Figure 2). After a visually confirmed feeding
event, predation tags were continuously monitored for a change in signal
(referred to as “triggering”) using a laptop running the HTI Acoustic Tag
software. The predation tag acoustic signal is activated in the gut by a
digestible fuse.
The predation tags were designed so that the tag signal would permanently
change and would display a different signal visualization.
Data from the 60 tags tested were processed in Mark Tags software (Figure
3).
Of the 60 predation tags fed to striped bass, 54 triggered indicating that the
Chinook salmon had been eaten. The time to trigger was calculated by
subtracting the time (and date) a striped bass ate the tagged Chinook salmon
from the trigger time (and date).
The average time to trigger was 59:15:11 with the minimum and maximum
times to trigger = 22:18:00 and 140:01:00 , respectively (Figure 4). The
standard deviation was 28:06:37.
We proved that the predation tags would work, however we do not believe the
tags are ready for widespread use in the field due to the 10% false negatives
and relative imprecision at which the tags triggered. In addition, we would
suggest that the predation tag be redeveloped to trigger in less than a couple
of hours so that fine scale fish behavior studies could get more information
from these tags such as these (Figure 5). We think that a failure rate of less
than 1% and a time to trigger of 1 hour or less would be preferred.
Defecated Tag
in Tank
Striped Bass
Six of the predation tags tested did not trigger inside the striped bass and were
considered to be false negatives. Of these six false negatives, 4 were defecated
by the striped bass before triggering, 1 never triggered, and 1 triggered at a
time so close to when the tag was defecated that we categorized it as
“unknown fate”. There were no false positives in the control Chinook
Salmon. Our controls were as follows: 20 live Chinook Salmon, implanted
with the predation tags in the pre-triggered state, were held for over 30 days.
Results Continued
Figure 3. A visualization of an actual predation tag triggering, inside a striped bass,
detected on a hydrophone. The image for this figure was captured from HTI
software that was designed to interpret tag data.
Figure1. The prototype predation tag.
Figure 4. A box and whisker plot of the time to trigger data showing
that the majority of tags triggered after 40 hours and before 70 hours,
despite the outliers. The average trigger time is displayed as a red dashed
line.
Triggering event
indicated by
appearance of extra
line.
Wires of digestible fuse
Chinook salmon and HTI tag
Figure 5. The above visualization of a predator avoidance shows
the path of a tagged striped bass in red, and the path of a tagged
salmonid, in this case a steelhead (Oncorhynchus mykiss), in green.
The elapsed time is roughly 30 minutes in duration.
References
Vogel, D.A. 2011. Evaluation of fish entrainment in seven unscreened Sacramento River
diversions, 2010. Report prepared for the Anadromous Fish Screen Program, CALFED
Ecosystem Restoration Program, U.S. Bureau of Reclamation, U.S. Fish and Wildlife Service,
NOAA Fisheries, and the California Department of Fish and Game. Natural Resource
Scientists, Inc. February 2011. 77 p. plus appendices.
Figure 2. Model
290 Acoustic Tag
Receiver