Does Lower Crab Creek in the Eastern Washington Desert Have a Native Population of Chinook Salmon?

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AbstractLower Crab Creek (LCC) in eastern Washington is a groundwater‐fed tributary to the Columbia River at river kilometer 661. The creek traverses agriculturally modified desert habitat, and in several reaches the water quality is poor, summer water temperatures are lethal to fish, and stream habitat is degraded. The creek was thought to be unsuitable for salmonids, yet fall‐run Chinook salmon Oncorhynchus tshawytscha spawn and rear in it. The origin of these fish is uncertain since it is unclear whether LCC was a perennial creek prior to the hydrologic changes in the Columbia River basin stemming from the Columbia Basin Irrigation Project in the 1950s. We used genetic analyses to examine the hypotheses that these fish are (1) random strays, (2) a population founded since the 1950s (by wild or hatchery strays), or (3) an established native population. Chinook salmon juveniles and adults were collected in LCC and genetically characterized with the Chinook salmon microsatellite DNA locus suite in the Genetic Analysis of Pacific Salmonids database. The LCC population of Chinook salmon was found to be significantly different from interior Columbia River basin hatchery and wild populations and to have alleles that are absent from proximal populations. Lower Crab Creek Chinook salmon showed no evidence of recent founding and had genetic diversity, allelic richness, and effective population size similar to those of other Columbia River basin Chinook salmon. The data suggest that a genetically distinct, native population of Chinook salmon inhabits LCC that has adapted to the rigorous environment.