Hard choices in assessing survival past dams — a comparison of single- and paired-release strategies

Canadian Journal of Fisheries and Aquatic Sciences
By: , and 

Links

Abstract

Mark–recapture models are widely used to estimate survival of salmon smolts migrating past dams. Paired releases have been used to improve estimate accuracy by removing components of mortality not attributable to the dam. This method is accompanied by reduced precision because (i) sample size is reduced relative to a single, large release; and (ii) variance calculations inflate error. We modeled an idealized system with a single dam to assess trade-offs between accuracy and precision and compared methods using root mean squared error (RMSE). Simulations were run under predefined conditions (dam mortality, background mortality, detection probability, and sample size) to determine scenarios when the paired release was preferable to a single release. We demonstrate that a paired-release design provides a theoretical advantage over a single-release design only at large sample sizes and high probabilities of detection. At release numbers typical of many survival studies, paired release can result in overestimation of dam survival. Failures to meet model assumptions of a paired release may result in further overestimation of dam-related survival. Under most conditions, a single-release strategy was preferable.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Hard choices in assessing survival past dams — a comparison of single- and paired-release strategies
Series title Canadian Journal of Fisheries and Aquatic Sciences
DOI 10.1139/cjfas-2015-0480
Volume 74
Issue 2
Year Published 2017
Language English
Publisher NRC Research Press
Contributing office(s) Coop Res Unit Leetown
Description 13 p.
First page 178
Last page 190