Overlap of Spatial and Temporal Spawning Distributions of Spring and Summer Chinook Salmon Results in Hybridization in the Upper Columbia River

Abstract

AbstractThe upper Columbia River in Washington State (main‐stem and tributary habitat between McNary and Chief Joseph dams) is inhabited by two major lineages of Chinook Salmon Oncorhynchus tshawytscha: endangered spring Chinook Salmon and summer Chinook Salmon, which are not Endangered Species Act (ESA) listed. The lineages are highly genetically divergent from one another, and historically, spatial and temporal isolating mechanisms maintained these genetic differences. Both lineages occur in the Entiat River, a system where anthropogenic activity has changed habitat, flows, species composition, and the distribution of the two lineages over the past century. We examined the spatial and temporal overlap in spawning distributions between Entiat River spring and summer Chinook Salmon, and we used genetic markers to assess the level of introgression between lineages. Redd surveys were conducted from 2003 to 2017 to describe spatial and temporal spawning patterns of both lineages. There was temporal overlap in spawning between lineages in several years and considerable spatial overlap in redd locations annually. We genotyped subyearling juvenile Chinook Salmon captured in the Entiat River from 2009 to 2014 at 90 single nucleotide polymorphism loci to determine lineage and hybridization status. Genetic analysis revealed that hybridization between lineages does occur, albeit at relatively low rates (2.6% of subyearling juveniles genotyped). We detected hybrids each year samples were collected, and they were distributed throughout the Entiat River basin. Hybridization between lineages of Chinook Salmon could result in introgression and a loss of genetic diversity between the lineages and/or a loss of production by ESA‐listed spring Chinook Salmon. The presence of hybrids warrants concern for ESA‐listed spring Chinook Salmon in both the Entiat River system and throughout the upper Columbia River basin.