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Chapter 2 Yellowstone Cutthroat Trout Oncorhynchus clarki bouvieri Bruce E. May Forest Fisheries Biologist USDA Forest Service Gallatin and Custer National Forests 10 E. Babcock Avenue, Box, 130 Bozeman, Montana 59771 INTRODUCTION The information contained in this status review focuses upon Yellowstone cutthroat trout (Oncorhyn- chus clarki bouvie,,), a principle subspecies of cutthroat trout that historically occupied the upper portion of the Snake River, within the Columbia River basin, and the upper Yellowstone River, within the Missouri River basin. This subspecies of cutthroat trout along with westslope cutthroat (0. c. lewis/), Lahontan cutthroat (0. c. henshawi), Bonneville cutthroat (0. c. utah), Paiute cutthroat (0. c. seleniris), Colorado River cutthroat (0. c. pleuriticus), Greenback cutthroat (0. c. stomias), Rio Grande cutthroat (0. c. virginalis), and Yellowfin cutthroat (0. c. macdonaJdl) were the primary trout that occupied the lakes and streams of the western United States (Behnke 1992). In addition to these taxonomically acknowledged subspecies, there are other cutthroat forms (i.e. finespotted Snake River cutthroat, Humboldt cutthroat, Alvord cutthroat and Whitehorse cutthroat) which inhabited specific locations and exhibited unique phenotypic characteristics (Behnke, 1979 and 1992). General concern for the well being of these native trout species has been elevated as a result of recent status assessments (Williams et al. 1989 and Warren and Burr 1994). These status reports pointed to a dramatic decline in the status of many freshwater fish species with as many as 364 freshwater fish (about one-third of the American native freshwater fishes) identified as endangered, threatened or of special concern (Williams et aI. 1989). The situation is particularly bleak within the western states (Warren and Burr 1994) which have a proportionately higher percentage of imperiled native species. Western trout (Behnke 1976) and salmon (Nehlsen et al. 1991) have suffered cata- strophic declines in abundance due to essentially similar factors (e.g. exotic species introduction, habitat degradation and over harvest). Concern for the status of western cutthroat prompted the Forest Service to initiate Habitat Conserva- tion Assessments (HCA) for many interior cutthroat trout subspecies. The information contained in this HCA will focus on Yellowstone cutthroat trout (including the fine spotted cutthroat of the upper Snake River). The goal associated with this Yellowstone cutthroat trout HCA is to provide information linked to habitat conditions necessary to assure the long term survival of both large spotted and fine spotted forms. In addition, population status is addressed and related to habitat and species man- agement within the historic range of the Yellowstone cutthroat trout subspecies. 11