Source stock contribution to restoration of westslope cutthroat trout in cherry creek, Madison County, Montana
Principle Investigators
Dr. Andrew Whiteley, University of Montana
Dr. Ryan Kovach, University of Montana
Dr. Donovan Bell, Montana Fish Wildlife and Parks
Dr. Carter Kruse, Turner Institute of Ecoagriculture
Rationale.
Embryos from five wild or hatchery populations were used to establish a population of westslope cutthroat trout in the renovated (i.e., piscicide treatment) habitat of upper Cherry Creek, a tributary to the Madison River, with the hypothesis that embryos from source populations with habitats that were more similar to Cherry Creek would survive better. Further, there is a growing body of evidence that source populations with increased genetic diversity will have higher survival. Tissue samples were collected from multiple generations of the growing population of cutthroat trout in Cherry Creek to ultimately test for source stock contribution to the genetic makeup of subsequent generations. Here, the Institute used samples from the upstream reaches of the watershed to test whether genetic diversity of source individuals is a key component for successful establishment of native trout populations in new or renovated habitats.
Outcomes.
Introductions are an increasingly important conservation tool, but few long-term studies have examined how source populationselection influences outcomes. We examined the long-term (approximately 4 generations) genetic outcomes of a large–scale,mixed-source introduction of westslope cutthroat trout in Cherry Creek,Montana.We testedwhether source populationcontribution deviated from neutral expectations (a proxy for fitness), and whether this correlated with source population characteristics.The two donor stocks with the lowest genetic variation had reduced contributions to the final population, whereasthose with the highest genetic variation exceeded neutral expectations by 152%–198%. Source contribution was strongly associatedwith genetic variation (R2 = 0.6). Nearly every fish in the final study year had mixed ancestry, and mean observedheterozygosity reached its highest recorded level, surpassing any one source. Our results suggest that using multiple sourcesand sources with higher variation may improve the outcomes of conservation introductions across multiple generations.
Bell, D.A., R. Kovach, M.R. Campbell, T.A. Delomas, L. Nelson, P. Clancey, B. Shepard, J. Williams, C. Kruse, and A.R. Whiteley. 2026. Long-term genetic outcomes of a mixed-source introduction of westslope cutthroat trout. Canadian Journal of Fisheries and Aquatic Sciences 83. doi.org/10.1139/cjfas-2025-0417.
