Population Structure of Coastal Cutthroat Trout in Mt. Hood National Forest

The U.S. Fish and Wildlife Service (USFWS) and U.S. Forest Service (USFS) collaborated on a project to investigate the cutthroat trout (Oncorhynchus clarki clarki) population structure and prevalence of hybridization with rainbow trout (Oncorhynchus mykiss) in streams connected to the Mt. Hood National Forest and Columbia River National Gorge Scenic Area (NSA).  We collected genetic samples from twenty-five sites in the Hood River watershed, Fifteenmile watershed, and nearby tributaries to the Columbia River, and two sites from the lower Columbia River.  Our results suggest that there are as many as eleven distinct populations of coastal cutthroat trout on the eastside of Mt. Hood National Forest and the NSA. The F_ST values suggest that many populations on the Mt. Hood and NSA are as isolated from one another as they are from populations in the lower Columbia River.  Both the correspondence analysis and STRUCTURE identified two outlier groups: 1) Clear Branch and 2) Upper Dog River, Crow Creek, and SF Mill Creek, both of which are upstream of high elevation barriers.  Hybridization ranged from 0% to 28% among the sample sites, and more hybrids were detected below barriers than above.  We plan to incorporate additional information on sampling techniques, geography, and site environmental data to allow broader inferences based on the current analysis.