Quantification of Hungry Horse Reservoir Water Levels Needed to Maintain or Enhance Reservoir Fisheries. Annual Report, October 15, 1983-April 30, 1985

摘要

The study was initiated to determine the effects of reservoir operation upon principal gamefish species in Hungry Horse Reservoir and to quantify seasonal water levels needed to maintain or enhance the reservoir fishery. Stream habitat surveys were conducted on 84 reaches in 62 tributaries. Adfluvial cutthroat trout spawning and rearing habitat appeared to be confined to stream reaches with a gradient less than 10%. Hungry Horse Reservoir was isothermal from approximately mid-November to mid-May, thermally stratified from mid-June through September and ice-covered from mid-January to about mid-April. Specific conductivity, pH, and dissolved oxygen values were generally in the optimum range for westslope cutthroat trout and appeared to have little direct influence on fish distribution. Water temperature had a major influence in fish distribution and activity through its regulation of metabolism, spawning periodicity and food availability. The annual refill and drawdown cycle had large impacts upon the morphometrics and thermal stability of the reservoir. The drawdown period caused large reductions in the surface area, volume, shoreline length, wetted bed area volume in euphotic zone and hydraulic-residence times. These changes in reservoir habitat appeared to have adverse effects upon fish food availability and reduced the quality and quantity of living space for most fish species. This probably translates into reduced growth and increased mortalities for westslope cutthroat trout during periods of extreme drawdown. The piscivorous bull trout may benefit from the diminished living space associated with drawdown. Predation efficiency should increase as fish are concentrated into less area. 63 refs., 29 figs., 20 tabs. (ERA citation 10:041461)