Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4675
Title: Influence of sex, migration distance, and latitude on life history expression in steelhead and rainbow trout (Oncorhynchus mykiss)
Author: Haley A. Ohms, Matthew R. Sloat, G. H. Reeves, Chris E. Jordan, Jason B. Dunham
Publication Year: 2013
Journal: Canadian Journal of Fisheries and Aquatic Sciences
Volume: 71
Issue: 1
Pages: 70-80
Keywords: salmon,life history,steelhead,rainbow trout,

In partially migratory species, such as Oncorhynchus mykiss, the emergence of life history phenotypes is often attributed to fitness tradeoffs associated with growth and survival.  Fitness tradeoffs can be linked to reproductive tactics that vary between the sexes, as well as the influence of environmental conditions.  We found that smolts are more likely to be female in nine populations throughout western North America, in support of the hypothesis that anadromy is more likely to benefit females.  This bias was not related to migration distance or freshwater productivity, as indicated by latitude.  Within one resident population we measured the sex ratio, and did not observe a male bias, despite a high female bias among smolts in that system.  We suggest this is the result of a high frequency of residents in that population, and provide a simulation to demonstrate this relationship.  Overall, our results are consistent with the hypothesis that life history expression is equally plastic in male and female O. mykiss, which further suggests that conservation of steelhead and rainbow trout are not independent activities.

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Theme: Recovery, Rebuilding and Sustainability of Marine and Anadromous Species
Foci: Investigate ecological and socio-economic effects of alternative management strategies or governance structures.
Characterize vital rates and other demographic parameters for key species, and develop and improve methods for predicting risk and viability/sustainability from population dynamics and demographic information.