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

Environmental Biology of Fishes

By:
, , ,
DOI: 10.1007/s10641-012-0016-3

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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:
Springer
Publisher location:
Amsterdam, Netherlands
Contributing office(s):
Western Fisheries Research Center
Description:
9 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Environmental Biology of Fishes
First page:
165
Last page:
173
Number of Pages:
9
Country:
United States
State:
California