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I I I ;. I I I I I I I I I I I, I I I I I flJ ,/''J'~)~' f;' :......J ~ Assessment of Kokanee Salmon Transport Through Blue Mesa Powerplant, Colorado, During the Spring and Summer of 1994-1996 By Gordon Mueller, U.S. Geological Survey Steve Hiebert, Bureau of Reclamation Denver, Colorado Summary: Fish transport rates through Blue Mesa Powerplant were measured using a large sieve net during the spring and summer of 1994, 1995, and 1996. Samples indicated the majority (96%) of fish were small (30-120 mm) kokanee salmon and which were being lost at a rate of .0001 to .1400 fish/acre-foot (8.107e to 8/1.135e-fish/m'l. Estimated total fish passage during June, July and August of each year was calculated at 770 for 1994, 60,837 for 1995, and 11,007 for 1996. This represents .05 to 4 percent of the total numbers of kokanee stocked during this period. There were no clear trends regarding fish passage; rates varied daily, seasonal1y, and year to year. In 1994, sampling prior to high releases suggested more (58%) fish were lost during the night. However, during higher releases in 1995 and 1996, passage rates (88 and 96% respectively} increased during daylight hours. We believe entrainment, or passage may actually be a complex association of fish behavior, reservoir elevations, season, and the volume of water released. More refined and lengthier investigations are needed to better understand what physical or biological conditions stimulate these losses. " Kokanee salmon distribution, densities, and population structure in the reservoir was determined using mobile hydroacoustic fish survey equipment. Fish were not found concentrated in the intake channel. Average fish densities were at or below values measured at other locations in the reservoir. We did detect the normal diel migration of fish in the water column. At night, fish were dispersed throughout the upper water column and during the day fish schooled and moved to deeper depths. Less than 6 percent of