Quantification of Hungry Horse Reservoir Water Levels Needed to Maintain or Enhance Reservoir Fisheries, 1984 Final Report.

This report reviews activities of the Hungry Horse Reservoir fisheries study from May 16-October 14, 1983. The first six months of the project were concerned with testing of equipment and developing methodologies for sampling physical-chemical limnology, fish food availability, fish food habits, seasonal distribution and abundance of fish, migration patterns of westslope cutthroat trout and habitat quality in tributary streams. Suitable methods have been developed for most aspects of the study, but problems remain with determining the vertical distribution of fish. Catch rates of fish in vertical nets were insufficient to determine depth distribution during the fall. If catches remain low during the spring and summer of 1984, experimental netting will be conducted using gang sets of standard gill nets. Purse seining techniques also need to be refined in the spring of 1984, Sample design should be completed in 1984. A major activity for the report period was preparation of a prospectus which reviewed: (1) environmental factors limiting gamefish production; (2) flexibility in reservoir operation; (3) effects of reservoir operation on fish populations and (4) model development. Production of westslope cutthroat trout may be limited by spawning and rearing habitat in tributary streams, reservoir habitat suitability, predation during the first year of reservoir residence and fish food availability. Reservoir operation affects fish production by altering fish habitat and food production through changes in reservoir morphometrics such as surface area, volume, littoral area and shoreline length. The instability in the fish habitat caused by reservoir operation may produce an environment which is suitable for fish which can utilize several habitat types and feed upon a wide variety of food organisms. Analysis of factors governing reservoir operation indicated that some flexibility exists in Hungry Horse operation. Changes in operation to benefit gamefish populations would have little impact on total power production, but would entail shifts in the generation schedule. We hope to develop, in cooperation with the USGS, a model which will predict the effects of reservoir operation on fish production. The model will have a food component based on energy flow through successive trophic levels to fish and a habitat component based on habitat availability and habitat preferences of species by life-stage