Survival and Straying of Hatchery Steelhead following Forced or Volitional Release

Abstract

In this study, conducted over four release years, we compare the performance of hatchery steelhead Oncorhynchus mykiss that were force-released (FR) from acclimation ponds with that of fish given a 2-week volitional release (VR). After fish were released into streams, we monitored smolt out-migration travel times and survival to Lower Granite Dam on the Snake River using passive integrated transponder (PIT) tags in a subsample of each release group. To better understand the out-migration characteristics of volitionally departing fish, we also captured and PIT-tagged fish as they exited ponds in the first and last 24 h of VR. Across all release groups, travel time was 3% faster for fish that were forced from acclimation ponds than for VR groups; however, the average survival of VR groups (65.0%) was significantly higher than that of FR groups (58.6%). On average, fish that departed acclimation ponds in the first 24 h of VR took 6 d longer to reach Lower Granite Dam and had lower survival (50.3%) than those departing in the last 24 h (56.9%), though these differences were not statistically significant. We estimated smolt-to-adult survival and a stray rate index for the FR and VR groups based on recoveries of coded-wire-tagged adults. Across all releases, smolt-to-adult survival was not significantly different between groups (FR = 0.63%, VR = 0.59%), and the same was true for the stray rate index (FR = 10.9%, VR = 10.6%). Our finding that VR provided no postrelease survival benefit is consistent with the results of other published studies, but this is the first study to quantify the stray rate in relation to VR.

Received September 14, 2010; accepted November 15, 2010

ACKNOWLEDGMENTS

Funding for this research was provided by the Lower Snake River Compensation Plan of the U.S. Fish and Wildlife Service. This study could not have been completed without the dedicated work of many biologists and hatchery managers and personnel; we thank them all for their efforts. We are especially grateful for assistance from Mike Gribble, Greg Davis, Ray Hill, Debra Eddy, Timothy Whitesel, Steven Parker, staff of the ODFW La Grande Fish Research office and the Irrigon and Wallowa Fish Hatcheries, and ODFW fish tagging supervisors and taggers. Finally, we thank two anonymous reviewers for their helpful comments.

Notes

^aThousands.

^aNinety-five percent confidence interval.

^aNinety-five percent confidence interval.