"January, 1987."

Includes bibliographical references (p. 31-33)

EXEC. SUMMARY (SN 85080) : This study is part of the Northwest Power Planning Council's resident fish and wildlife plan, which is responsible for mitigating damages to fish and wildlife resources caused by hydroelectric development in the Columbia River basin. The major goal of this study was to provide estimates of fishery losses to the Flathead system as a result of the completion of Hungry Horse Dam and to propose mitigation alternatives for enhancing the fishery. Hungry Horse Reservoir (HHR) flooded approximately 57 km of the South Fork of the Flathead River and portions of 37 tributary streams with potential use for salmonids. Additionally, the dam blocked access to about 38 percent of the total drainage area available for spawning salmonids migrating upstream from Flathead Lake. A total of 69 km of potential cutthroat tributary habitat was inundated by Hungry Horse Reservoir. Using stream order and gradient as indices of cutthroat densities, we estimated that potential habitat which would support an average of about 21,000 cutthroat juveniles was lost in these tributary streams. Based on the gradients of these streams inundated, we calculated that 89 percent of these fish were adfluvials destined for Flathead Lake and the rest resident tributary fish. Based on population estimates from the river above HHR, we calculated that potential habitat for about 12,000 juvenile cutthroat was lost when the South Fork Flathead River was inundated. These fish were also adfluvials destined for Flathead Lake. Access to tributary habitat that would support approximately 165,500 adfluvial cutthroat juveniles was lsot in the upper South Fork when the dam was completed. Based on migration rates for the Kootenai system, we calculated that about 65,500 adfluvial juvenile cutthroat were lost to Flathead Lake annually from the river and tributary system. Based on spawning gravel surveys and spawner escapement estimates from Hungry Horse Creek, potential recruitment of about 2,350 cutthroat juveniles were lost to the reservoir population if all problem road culverts identified were complete migration barriers. By comparing spawning escapement estimates and drainage areas for the North and Middle Forks of the Flathead River, potential habitat for about 2,100 adult bull trout was lost to Flathead Lake annually from blocked access to the South Fork due to dam construction. Construction of Hungry Horse Dam had the greatest adverse impacts on cutthroat and bull trout from Flathead Lake and mitigative measures should be taken to offset these losses, if biologically and economically feasible. Also, other losses to fish and wildlife have been documented in the Flathead basin due to hydroelectric facilities and their operation. Some of these research projects will not be completed until 1989, when mitigation will be recommended using a basin-wide approach. Since HHR is at the headwaters of the Columbia system, mitigative measures may also affect downstream projects. Therefore, we presented an array of possible mitigation alternatives for consideration by decision-makers, with suggestions on the ones we feel are the most cost effective. Possible mitigation measures included: (1) a feasibility/monitoring study to determine if the Bigfork fish ladder can be operated and maintained to pass fish upstream during all seasons and if the Swan drainage can significantly contribute to natural reproduction for Flathead Lake, (2) improve fish passage at barrier road culverts, (3) various stocking strategies using hatchery plants, (4) operation of Hungry Horse Dam to benefit game fish in the reservoir, (5) rehabilitation of spawning and rearing habitat in previously degraded Flathead basin tributaries, and (6) construction, operation and maintenance of spawning channels to enhance production. Monitoring should be initiated to determine the effectiveness of mitigation measures implemented and ensure a successful program.

DE-AI79-85BP23638 85-23

RF._.018.87.__ Northwest Power & Conservation Council Collection Management Mou