Status of Yellowstone Cutthroat Trout in Wyoming Waters

Most subspecies of interior cutthroat trout Oncorhynchus clarki have suffered dramatic declines in range and number. We assessed the status of genetically pure Yellowstone cutthroat trout O. clarki bouvieri on predominantly public lands in three major watersheds of northwestern Wyoming (Greybull River and North and South Forks of the Shoshone River) between 1994 and 1997. These river basins encompass the majority of remaining habitat outside of Yellowstone National Park with potential to contain Yellowstone cutthroat trout, and little information on them was available. Only 26% of the 104 streams found to contain trout still support genetically pure Yellowstone cutthroat trout. Extant Yellowstone cutthroat trout occupied 245 of 822 km of the perennial streams that contained trout, suggesting native trout have been displaced by or hybridized with exotic salmonids in nearly three‐quarters of the available habitat in these watersheds. The four remaining populations were widely separated in the watersheds and had populations that ranged from 900 to 23,000 age‐1 and older individuals and that appeared genetically and demographically viable. However, because the threats of hybridization and competition remain, the current cutthroat trout populations cannot be considered secure or likely to persist over the long term. Yellowstone cutthroat trout have suffered larger than expected declines in their distribution in Wyoming outside of Yellowstone National Park largely because of nonnative salmonid introductions and invasions. We recommend immediate management intervention to control exotic salmonids and reestablish large, genetically pure, allopatric populations of Yellowstone cutthroat trout.