Status Review for Westslope Cutthroat Trout in the United States Status Review for Westslope Cutthroat Trout in the United States
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Appendix 53 Status Review for Westslope Cutthroat Trout in the United States Status Review for Westslope Cutthroat Trout in the United States September 1999 United States Department of the Interior U.S. FISH AND WILDLIFE SERVICE Regions 1 and 6 Portland, Oregon and Denver, Colorado Table of Contents I. Executive Summary..........................................................1 II. Introduction and Approach ....................................................4 Endangered Species Act Requirements.......................................4 Petition History for the Westslope Cutthroat Trout ..............................4 Public Comment Period...................................................6 Response to the Information Request ........................................6 Distinct Population Segments ..............................................6 State Game and Fish Department Information..................................9 Classification of WCT by Management Agencies...............................9 Importance of Introgressed WCT in the Status Review..........................10 Importance of Introduced WCT Stocks in the Status Review.....................11 ICBEMP Data .........................................................12 Data Analyses .........................................................13 Status Review Team ....................................................13 Acknowledgments ......................................................13 III. Life History and Ecology of Westslope Cutthroat Trout................................................15 Description............................................................15 Taxonomy ............................................................15 Historic Distribution ....................................................15 Life History ...........................................................16 Habitat Use............................................................17 Environmental Tolerances................................................18 Movements............................................................19 Interactions with other Fish Species ........................................19 IV. Geographic Summaries of Biological Information for Westslope Cutthroat Trout.............................................21 Oldman River Drainage..................................................21 Missouri River Headwaters Drainage .......................................22 Lower Missouri River Drainage............................................26 Kootenai River Drainage, Montana.........................................31 Clark Fork River Drainage................................................34 Flathead River Drainage .................................................38 Pend Oreille Drainage, Idaho ..............................................42 Pend Oreille Drainage, Washington .........................................48 Spokane River Drainage .................................................51 Kootenai River Drainage, Idaho ...........................................58 i Upper Columbia River Drainage, Washington ................................62 Clearwater River Drainage................................................68 Salmon River Drainage ..................................................74 John Day River Drainage .................................................84 V. Summary of Factors and Threats Affecting Westslope Cutthroat Trout................................................89 Oldman River Drainage..................................................89 Missouri River Headwaters Drainage .......................................90 Lower Missouri River Drainage............................................92 Kootenai River Drainage, Montana.........................................94 Clark Fork River Drainage................................................96 Flathead River Drainage .................................................98 Pend Oreille Drainage, Idaho .............................................100 Pend Oreille Drainage, Washington ........................................108 Spokane River Drainage ................................................114 Kootenai River Drainage, Idaho ..........................................122 Upper Columbia River Drainage, Washington ...............................128 Clearwater River Drainage...............................................136 Salmon River Drainage .................................................140 John Day River Drainage ................................................144 VI. Ongoing Regulatory and Conservation Actions .................................148 Montana.............................................................148 Idaho................................................................150 Washington ..........................................................151 Oregon..............................................................151 VII. Conclusions ............................................................152 Distribution of Westslope Cutthroat Trout ..................................152 Genetic Characteristics of WCT Stocks ....................................153 Timing of the Principal Decline in the WCT Population .......................154 Viability of Small WCT Stocks ...........................................156 VIII. Findings ...............................................................157 IX. References..............................................................159 Reports and Published Papers ............................................159 Letters and other Documents.............................................173 Personal Communications...............................................178 X. Appendix Tables .........................................................183 ii I. Executive Summary On June 6, 1997, the U.S. Fish and Wildlife Service (Service) received a formal petition to list the westslope cutthroat trout Oncorhynchus clarki lewisi as threatened throughout its range pursuant to the Endangered Species Act (ESA) of 1973. The westslope cutthroat trout (WCT) is one of 14 subspecies of cutthroat trout O. clarki native to interior regions of western North America. The historic distribution of WCT in the United States consists of several major drainages of the upper Columbia River basin (Idaho and Montana), the Methow River and Lake Chelan drainages (Washington), the John Day River drainage (Oregon), the headwaters of the South Saskatchewan River (Montana), and the upper Missouri River basin (Montana and Wyoming). The historic range of WCT is the most widespread geographically among the 14 subspecies of inland cutthroat trout. On June 10, 1998, the Service published a notice in the Federal Register of a 90-day finding that an amended WCT petition (received January 25, 1998) provided substantial information indicating that the petitioned action may be warranted. The Service promptly began a status review for WCT to assemble information pertinent to the question of whether the listing of the subspecies as threatened or endangered under the ESA was warranted. The Service subsequently received information pertinent to WCT from several state game and fish departments, the U.S. Forest Service, National Park Service, tribal governments, and private corporations, as well as private citizens, organizations, and other entities. The Service also reviewed information on WCT obtained from refereed journal articles, agency reports and file documents, telephone interviews and written correspondence with natural resources managers familiar with WCT, and other sources. For the purposes of the status review, the Service assumed that the fish stocks that the state game and fish departments classified as WCT represented that subspecies, even though the precise genetic characteristics of those stocks may not have been known or the stocks consisted of intercross progeny that were the product of some low or non-detectable level of interbreeding between WCT and another fish species. In addition, the Service evaluated WCT status solely on the basis of WCT stocks that presently occur within the historic range of the subspecies. The Service found no compelling evidence in support of recognizing distinct population segments for WCT. Instead, a single WCT population was recognized for purposes of the status review. The Service found that WCT presently inhabit about 4,275 tributaries or stream reaches that collectively encompass more than 23,000 linear miles of stream habitat, distributed among 12 major drainages and 62 component watersheds in the Columbia, Missouri, and Saskatchewan River basins. In addition, WCT presently inhabit 6 lakes in Idaho and Washington and at least 20 lakes in Glacier National Park, Montana. Although WCT stocks that formerly occupied large, mainstem rivers and lakes and their principal tributaries are reduced from their historic levels, to a degree that cannot be determined precisely because definitive historic data are limited, the Service found that viable, self-sustaining WCT stocks remain widely distributed throughout the 1 historic range of the subspecies, most notably in headwater areas. Evidence from the Missouri River basin indicated that a conspicuous decline in WCT stocks occurred early in the twentieth century. That decline was largely attributed to rapid, abundant colonization of mainstem rivers and their major tributaries by one or more introduced, nonnative fish species (i.e. brown trout Salmo trutta and rainbow trout O. mykiss) that had adverse effects on WCT. There was also evidence,