Size-selective mortality of steelhead during freshwater and marine life stages related to freshwater growth in the Skagit River, Washington

Transactions of the American Fisheries Society
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Abstract

We evaluated freshwater growth and survival from juvenile (ages 0–3) to smolt (ages 1–5) and adult stages in wild steelhead Oncorhynchus mykiss sampled in different precipitation zones of the Skagit River basin, Washington. Our objectives were to determine whether significant size-selective mortality (SSM) in steelhead could be detected between early and later freshwater stages and between each of these freshwater stages and returning adults and, if so, how SSM varied between these life stages and mixed and snow precipitation zones. Scale-based size-at-annulus comparisons indicated that steelhead in the snow zone were significantly larger at annulus 1 than those in the mixed rain–snow zone. Size at annuli 2 and 3 did not differ between precipitation zones, and we found no precipitation zone × life stage interaction effect on size at annulus. Significant freshwater and marine SSM was evident between the juvenile and adult samples at annulus 1 and between each life stage at annuli 2 and 3. Rapid growth between the final freshwater annulus and the smolt migration did not improve survival to adulthood; rather, it appears that survival in the marine environment may be driven by an overall higher growth rate set earlier in life, which results in a larger size at smolt migration. Efforts for recovery of threatened Puget Sound steelhead could benefit by considering that SSM between freshwater and marine life stages can be partially attributed to growth attained in freshwater habitats and by identifying those factors that limit growth during early life stages.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Size-selective mortality of steelhead during freshwater and marine life stages related to freshwater growth in the Skagit River, Washington
Series title Transactions of the American Fisheries Society
DOI 10.1080/00028487.2014.901253
Volume 143
Issue 4
Year Published 2014
Language English
Publisher Taylor & Francis
Contributing office(s) Coop Res Unit Seattle
Description 16 p.
First page 910
Last page 925
Country United States
State Washington
Other Geospatial Skagit River