Relationship between Juvenile Fish Condition and Survival to Adulthood in Steelhead

Abstract

Understanding how individual characteristics are associated with survival is important to programs aimed at recovering fish populations of conservation concern. To evaluate whether individual fish characteristics observed during the juvenile life stage were associated with the probability of returning as an adult, juvenile steelhead Oncorhynchus mykiss from two distinct population segments (DPSs; Snake River and upper Columbia River) were captured, photographed to determine external condition (body injuries, descaling, signs of disease, fin damage, and ectoparasites), measured, classified by rearing type (hatchery, wild), marked with a PIT tag, and released to continue out-migration to the Pacific Ocean during 2007–2010. The PIT tags of returning adults were interrogated in fishways at hydroelectric dams on the lower Columbia River 1–3 years following release as juveniles. Juvenile-to-adult survival models were investigated independently for each DPS and indicated that similar individual fish characteristics were important predictors of survival to adulthood for both steelhead populations. The data analysis provided strong support for survival models that included explanatory variables for fish length, rearing type, and external condition, in addition to out-migration year and timing. The probability of a juvenile surviving to adulthood was positively related to length and was higher for wild fish compared with hatchery fish. Survival was lower for juveniles with body injuries, fin damage, and external signs of disease. Models that included variables for descaling and ectoparasite infestation, however, had less support than those that incorporated measures of body injuries, fin damage, and disease. Overall, results indicated that individual fish characteristics recorded during the juvenile life stage can be used to predict adult survivorship in multiple steelhead populations.

Received August 20, 2013; accepted February 14, 2014

ACKNOWLEDGMENTS

We thank B. Cramer, J. Tennyson, M. Carper, P. Loschl, and numerous technicians for their help in the field. The U.S. Army Corps of Engineers, Walla Walla District, provided funding to tag juvenile fish used in this study, for which we are grateful. We especially thank M. Plummer, B. Spurgeon, D. Tratchenbarg, and C. Pinney for providing access to Snake River dams and for providing logistical support. We thank the Chelan County Public Utility District, particularly S. Hemstrom and B. Keesee, for providing access to Rock Island Dam and for allowing us to work with their staff at the juvenile fish facility. The use of trade or product names does not constitute endorsement by the U.S. Government. All handling of live fish as part of this study followed protocols approved by the Institutional Animal Care and Use Committee at Oregon State University.