Homogenization of Fall-Run Chinook Salmon Gene Pools in the Central Valley of California, USA

Abstract We assessed the population genetic structure and temporal stability of genetic diversity from 1999 to 2001 in collections of fall-run Chinook salmon Oncorhynchus tshawytscha in California's Central Valley. Tests for genotypic differentiation at seven microsatellite loci revealed few significant pairwise comparisons between samples from five hatchery populations and eight naturally spawning populations throughout the Central Valley that were separated by 50–350 km. All collections were genetically homogeneous and failed to cluster with their nearest geographic neighbors. Likewise, evaluation of temporal change in genetic diversity revealed few changes over the 3 years of the study. Our results suggest that fall-run Chinook salmon throughout the Central Valley comprise a genetically homogeneous population that has lower among-population genetic diversity than fall-run Chinook salmon populations examined elsewhere over similar geographic scales. The lack of genetic distinction and the lack of tempor...