Genetic and Phenotypic Variation through the Migratory Season Provides Evidence for Multiple Populations of Wild Steelhead in the Dean River, British Columbia

Abstract

Abstract We provide evidence for previously undetected population structure in a wild run of summer steelhead Oncorhynchus mykiss within a river that has considerable recreational importance (Dean River, British Columbia). Data were gathered from an existing catch-and-release fishery and examined for phenotypic and genetic variation through the migratory season. Specifically, we compared fish captured in different periods during the migration: early (July 2-30), middle (July 31-September 5), and late (September 6-30). Age (freshwater and saltwater), sex ratio, and body girth did not differ significantly among these groups for females or males. Body length increased through the migratory season for both sexes, perhaps because late-migrating fish had more time to feed in the ocean. Based on genotypes at 10 microsatellite loci, early and late groups showed highly significant genetic differences (P < 0.001). Assignment tests were able to classify individuals back to early or late groups with 84% accuracy (122...