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

February 25, 2013

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.

Publication Year 2013
Title Adjusting survival estimates for premature transmitter failure: A case study from the Sacramento-San Joaquin Delta
DOI 10.1007/s10641-012-0016-3
Authors Christopher M. Holbrook, Russell W. Perry, Patricia L. Brandes, Noah S. Adams
Publication Type Article
Publication Subtype Journal Article
Series Title Environmental Biology of Fishes
Index ID 70043969
Record Source USGS Publications Warehouse
USGS Organization Western Fisheries Research Center