Evaluate status of pacific lamprey in the Clearwater River drainage, Idaho:annual report 2000

摘要

Recent decline of Pacific lamprey Lampetra tridentata adult migrants to the SnakeRiver drainage has focused attention on the species. Adult returns in 1995-1999 were more than ten magnitudes less than returns in the early 1960's. Human activities in the Snake River and Clearwater River drainages have altered ecosystem habitat in the last 100 years and likely the productive potential of Pacific lamprey habitat. Logging, stream impoundment, road construction, grazing, mining, and community development have dominated habitat alteration in the Clearwater River system and Snake River corridor. Hydroelectric projects in the Snake River corridor impact juvenile Pacific lamprey outmigrants and returning adults. Juvenile lamprey outmigrants potentially pass through turbines, turbine bypass and collection systems, and spillway structures at lower Snake River hydroelectric dams. Clearwater River drainage hydroelectric facilities including the Pacific Power and Light Dam on the Clearwater River in Lewiston, Idaho, impacted Pacific lamprey populations, however, the degree of impact is unknown (1920's-early 1970's). Hydroelectric dam construction (Harpster Dam) on the South Fork of the Clearwater River resulted in obstructed salmonid passage in the mid-1900's. Habitat alterations in the Snake River basin and Clearwater River drainage have had numerous negative effects on salmon Oncorhynchus spp. and steelhead trout O. mykiss populations (wild fish), but the magnitude of impacts on lamprey productivity and survival is unknown. Thorough understanding of Pacific lamprey habitat use and life history processes is needed to facilitate management and restoration of the species. Through Bonneville Power Administration support, the Idaho Department of Fish and Game began investigation into the status of Pacific lamprey populations in Idaho's Clearwater River drainage in 2000. Trapping, electrofishing, and spawning ground redd surveys were used to determine where Pacific lamprey persist in the South Fork of the Clearwater River drainage. Habitat surveys evaluating juvenile habitat use were primarily conducted in the Red River subbasin. Red River subbasin resource manipulations have resulted in elevated stream sediment, stream destabilization, riparian canopy reduction, and water temperature extremes. A total of 262 juvenile Pacific lamprey were captured during the 2000 field season. Sampling in the Red River drainage yielded the largest number of Pacific lamprey juveniles. Preliminary findings indicate Pacific lamprey juveniles, while present, are not numerous or widely distributed. Age of juveniles captured was determined using length frequency.