Adjusting survival estimates for premature transmitter failure: A case study from the Sacramento-San Joaquin Delta

Environmental Biology of Fishes
By: , and 

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Abstract

In telemetry studies, premature tag failure causes negative bias in fish survival estimates because tag failure is interpreted as fish mortality. We used mark-recapture modeling to adjust estimates of fish survival for a previous study where premature tag failure was documented. High rates of tag failure occurred during the Vernalis Adaptive Management Plan’s (VAMP) 2008 study to estimate survival of fall-run Chinook salmon (Oncorhynchus tshawytscha) during migration through the San Joaquin River and Sacramento-San Joaquin Delta, California. Due to a high rate of tag failure, the observed travel time distribution was likely negatively biased, resulting in an underestimate of tag survival probability in this study. Consequently, the bias-adjustment method resulted in only a small increase in estimated fish survival when the observed travel time distribution was used to estimate the probability of tag survival. Since the bias-adjustment failed to remove bias, we used historical travel time data and conducted a sensitivity analysis to examine how fish survival might have varied across a range of tag survival probabilities. Our analysis suggested that fish survival estimates were low (95% confidence bounds range from 0.052 to 0.227) over a wide range of plausible tag survival probabilities (0.48–1.00), and this finding is consistent with other studies in this system. When tags fail at a high rate, available methods to adjust for the bias may perform poorly. Our example highlights the importance of evaluating the tag life assumption during survival studies, and presents a simple framework for evaluating adjusted survival estimates when auxiliary travel time data are available.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Adjusting survival estimates for premature transmitter failure: A case study from the Sacramento-San Joaquin Delta
Series title Environmental Biology of Fishes
DOI 10.1007/s10641-012-0016-3
Volume 96
Issue 2
Year Published 2013
Language English
Publisher Kluwer Academic Publishers
Contributing office(s) Western Fisheries Research Center
Description 9 p.
First page 165
Last page 173
Country United States
State California
Other Geospatial Sacramento-San Joaquin Delta, San Joaquin River
Online Only (Y/N) N
Additional Online Files (Y/N) N
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