Evaluating Artificial Propagation Release Strategies for Recovering Endangered Snake River Sockeye Salmon

Abstract

AbstractAs a growing number of aquatic organisms become imperiled due to anthropogenic and environmental threats, there is an increasing need to implement captive propagation programs to conserve some species. These captive propagation programs can aid in the recovery of species, such as for Sockeye Salmon Oncorhynchus nerka, by providing individuals that can be used to supplement wild populations. The Snake River Sockeye Salmon Captive Broodstock Program implemented a comprehensive monitoring and evaluation plan to evaluate adult recruitment using three juvenile release strategies from excess eggs of captive females. Hatchery‐produced eyed eggs, presmolts, and smolts were released into the upper Salmon River basin to increase the abundance of individuals expressing an anadromous life history as a way to support population augmentation. A mixed‐effects logistic regression model used to evaluate egg‐to‐adult returns between release strategies indicated that release strategies differed from one another. Full‐term smolt production was observed to produce the highest recruitment among the release strategies and has become the focus of recovery efforts involving juvenile releases. The estimated odds of a fish (egg) returning as an adult were 9.7 times greater for smolts reared at the Oxbow Fish Hatchery and 3.6 times greater for smolts reared at the Sawtooth Fish Hatchery relative to eggs that were hatchery reared and released as presmolts or placed into in‐lake incubator boxes. The variation observed in productivity and in expression of life history traits among release strategies indicates that juvenile releases are not one size fits all, and we recommend undertaking a similar assessment to match observed outcomes with desired objectives when initiating supplementation programs.