Overlap of spatial and temporal spawning distributions of spring and summer Chinook Salmon results in hybridization in the upper Columbia River

The 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 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. We genotyped sub-yearling juvenile Chinook S...