Dan Drinan MS Student Department of Ecology Montana State University Thermal Adaptation of Westslope Cutthroat Trout Populations of westslope cutthroat trout (Oncorhynchus clarkii lewisi), a state species of special concern, have been on the decline throughout their native range. As of 2002, estimates state that westslope cutthroat trout inhabit only 59% of their historic range. Genetic introgressions mainly from rainbow trout (O. mykiss), but also from Yellowstone cutthroat trout (O. c. bouvieri), and habitat loss are the leading causes of this decline. Because of the rapid decline of westslope cutthroat trout, it is clear that management involvement is necessary. Currently, however, it is unclear as to what would be the best management practice to initiate. Because many local westslope cutthroat trout populations have very few individuals, there is a concern that inbreeding depression could lead to population collapse. Previous studies have shown that translocation projects have been successful, but what factors influence the success or failure of a translocation project needs further investigation. In addition, improper introduction of adversely adapted individuals could cause the detrimental problem of outbreeding depression. Because of these concerns, this study is designed to investigate the local adaptation of westslope cutthroat trout; to better assist management personnel make decisions about specific populations.

Contact: Dan Drinan ddrinan@montana.edu Montana Cooperative Fishery Research Unit 301 Lewis Hall Montana State University Bozeman, Montana 59717