Project

Tag Predation SOP for the Sacramento–San Joaquin River Delta

Goal: Development of a Standard Operating Procedure (SOP) for diagnosing and handling tag predation in acoustic telemetry studies of emigrating juvenile salmonids in the Sacramento–San Joaquin River Delta. This project involves: (1) analyzing existing telemetry data sets of predatory fishes to characterize movement patterns by species, season, and regions; (2) developing analytical approaches to reduce uncertainty, subjectivity, and effort of analysis in salmonid acoustic telemetry studies; and (3) standardizing methods and providing software tools for diagnosing detections of predated tags in future studies.

Date: 31 January 2022

Updates
0 new
0
Recommendations
0 new
0
Followers
0 new
3
Reads
0 new
24

Project log

Steve Whitlock
added a research item
Tag predation is recognized as a significant impediment to studying anadromous salmonids in California’s Central Valley, specifically Chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss). A variety of filtering approaches have been developed for addressing this issue since acoustic telemetry studies began over a decade ago. Much can be gained by considering past approaches to dealing with this issue, as well as studies on salmonid movement rates and regional predation risk. This document is a compilation and synthesis of the many references on the subject and also includes pertinent studies outside the region. The purpose of the document is to provide current and future researchers in the Central Valley with a set of resources that will help them contend with this issue during both the planning and analysis phases of their investigations. This report was presented to the Delta Science Stewardship Council, funding agency, on 6/29/2022.
Rebecca A. Buchanan
added a research item
Background Acoustic telemetry is a powerful tool for studying fish behavior and survival that relies on the assumption that tag detection reflects the presence of live study subjects. This assumption is violated when tag signals continue to be recorded after consumption by predators. When such tag predation is possible, it is necessary for researchers to diagnose and remove these non-representative detections. Past studies have employed a variety of data-filtering techniques to address the issue, ranging from rule-based algorithms that rely on expert judgements of behavior and movement capabilities of study subjects and their predators to automated pattern-recognition techniques using multivariate analyses. We compare four approaches for flagging suspicious tracks or detection events: two rule-based expert-opinion approaches of differing complexity and two unsupervised pattern-recognition approaches with and without data from deliberately tagged predators. We compare alternative approaches by applying these four filters to a case study of survival estimation of acoustic-tagged juvenile Chinook salmon ( Oncorhynchus tshawytscha ) in the San Joaquin River, California, United States. Results Filtering approaches differed in the number and composition of tags suspected of being consumed by predators; the largest differences occurred between the two broad categories, rule-based versus pattern recognition. All methods required some investigator judgement and all flagged a small subset (5%) of suspicious tags that had exceptionally long residence times and evidence of upstream transitions; 27% of tags showed evidence of predation based on at least one filter. The complex rule-based filter deemed the most tags suspicious (21%) and the simpler pattern-recognition method the fewest (10%). Reach-specific survival estimates from the four filters were mostly within 2% of the unfiltered estimates, but differences up to 11% were observed. Conclusions Sensitivity of survival results to tag predation and predator filtering depends on the study setting, spatiotemporal scale of inference, and habitat use of predators. Choice of filtering technique depends on the data available and knowledge of the study system. We recommend that survival studies include clear documentation of filtering methods and report on robustness of results to the filtering approach selected.
Steve Whitlock
added a project goal
Development of a Standard Operating Procedure (SOP) for diagnosing and handling tag predation in acoustic telemetry studies of emigrating juvenile salmonids in the Sacramento–San Joaquin River Delta. This project involves: (1) analyzing existing telemetry data sets of predatory fishes to characterize movement patterns by species, season, and regions; (2) developing analytical approaches to reduce uncertainty, subjectivity, and effort of analysis in salmonid acoustic telemetry studies; and (3) standardizing methods and providing software tools for diagnosing detections of predated tags in future studies.