Energetic, Morphological and Reproductive Traits in a Re-Introduced Population of Coho Salmon from the Wenatchee River, Washington

Since 1996, Yakama Nation fisheries resource managers have been reintroducing coho salmon (Oncorhynchus kisutch) into mid-Columbia River tributaries, where indigenous coho adapted to long migration are extinct. A substantially extended freshwater migration of more than 500 river kilometers continues to serve as a major selective force potentially driving the rate and scale of local adaptation in these developing populations. The present study examined how such conditions may have influenced the energetics, morphology and reproduction of coho from the Wenatchee River after two generations of reproductive isolation from its founding population. Comparisons were made with adult coho from the Bonneville Fish Hatchery to determine whether phenotypic differences in these attributes have emerged since the initial re-colonization. Results suggested that Wenatchee River coho may have begun the adult freshwater migration with higher somatic lipid content than Bonneville Hatchery coho, but that they were proportionally smaller than their lower river counterparts. However, egg size and fecundity in Wenatchee River females appeared to be similar to that of females from the founding population. This investigation concluded that Wenatchee River coho in the initial stages of local adaptation presented significant phenotypic differences and may continue to diverge from their founding population as they re-colonize their historic range in Middle Columbia River tributaries.