This study was undertaken in 1979 to assess impacts of various proposed power alternatives and flow regimes of Hungry Horse Reservoir on the fisheries of the Flathead River.This completion report includes results from the 1981-82 field season and discussions of results from the previous two field seasons concerning the effects of discharges from Hungry Horse Reservoir on kokanee abundance, migration, spawning and egg incubation.This report also addresses flow requirements for kokanee spawning and incubation and for rearing of other gamefish in the river including westslope cutthroat, bull trout and mountain whitefish.Abundance estimates of kokanee spawners and redd counts were made to assess the relative contributions of various segments of the river system to the population.
The abundance of westslope cutthroat trout Salmo clarki lewisi was estimated in three sections of the South Fork of the Flalhead River. We made two different Petersen mark-recapture estimates (angling only and angling with snorkeling) and compared them to a snorkel-expansion estimate. Anglers caught and snorkelers classified similar size-groups of cutthroat trout. The snorkelexpansion estimate was similar to the two Petersen estimates. In one section, we estimated total abundance at 452, 527, and 546 cutthroat trout/km by the hook-and-line Petersen, snorkel-Petersen, and snorkel-expansion methods, respectively. In a second section, we estimated 215 and 221 cutthroat trout/km by the snorkel-Petersen and snorkel-expansion methods, respectively. In a third section, we estimated 183 and 201 cutthroat trout/km by the snorkel-Petersen and snorkelexpansion methods, respectively. We concluded that, in large clear streams with little cover, the snorkel-expansion method provides a quick, reliable density estimate at relatively low cost.
This report was funded by the Bonneville Power Administration (BPA) , U.S. Department of Energy, as part of BPA's program to protect, mitigate, and enhance fish and wildlife affected by the development and operation of hydroelectric facilities on the Columbia River and its tributaries. The views in this report are the author's and do not necessarily represent the views of BPA.
This study developed a field method to examine emergence success of fry of westslope cutthroat trout Oncorhynchus clarki lewisi in relation to varying levels of fine substrate materials in a natural stream environment. We attempted to simulate natural incubation conditions in a stream by constructing cells with particle sizes and egg pockets characteristic of natural westslope cutthroat trout redds. We found a significant inverse relationship (r2 = 0.72, P < 0.005, N = 17) between fry emergence success, as measured by fry emergence traps, and the percentage of substrate materials less than 6.35 mm in diameter. Mean fry emergence success was 76, 55, 39, 34, 26, and 4%, respectively, in cells containing 0, 10, 20, 30, 40, and 50% substrate materials less than 6.35 mm. There were no significant differences in length or weight of fry emerging from the six gravel mixtures. Using the methods and results presented in this study, as well as previous laboratory results, resource managers could develop substrate quality guidelines for westslope cutthroat trout reproduction in streams affected by land management practices.
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