Genetic divergence and diversity reflect a predominant freshwater resident life history in Rainbow Trout from southwestern Alaska

Rainbow Trout Oncorhynchus mykiss in southwestern Alaska occupy coastal watersheds near the northern boundary of the species native range and support a world class wild trout sport fishery. Although low freshwater temperatures and a short growing season in this region may favor anadromy, these populations appear to exhibit a freshwater resident life history strategy. In this study we used genetic data to evaluate two hypotheses regarding the influence of the presumed migratory behavior of these Rainbow Trout on reproductive isolation among and within watersheds. The results were largely consistent with the predictions but there were exceptions. The data supported the hypothesis that the freshwater resident behavior precludes marine-mediated gene flow resulting in large genetic divergence and low admixture among watersheds. The estimate of FCT (among-watershed differentiation, 0.350) was large and reflected over 96% of the variation among all sampled aggregations (FST = 0.363). However, ...