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LONG-TERM CHANGES IN THE FISH COMMUNITY OF LOWER SAGEHEN CREEK, <br />CALIFORNIA <br />Don C. Erman <br />Department of Forestry and Resource Management <br />University of California <br />Berkeley, CA 94720 <br />A long-term study was made of impacts of a new reservoir on <br />upstream fish populations. The fish populations of Sagehen <br />Creek, California have been under study since 1951. In 1969, the <br />lowest section of the creek was flooded by Stampede Reservoir. <br />Soon after, populations of nine species, six of them native, <br />began to undergo changes. Large fluctuations in relative <br />abundance and simplification of the fish community have occurred. <br />Brook trout (Salvelinus fontinalis), speckled dace (Rhinichthys <br />osculus), mountain sucker (Catostomus platyrhynchus), and <br />mountain whitefish (Prosopium williamsoni) have become rare. <br />Lahontan redside (Richardsonius earegius), Tahoe sucker <br />(Catostomus tahoensis), brown trout (Salmo trutta), rainbow trout <br />(Salmo gairdneri), and Paiute sculpin (Cottus beldinai) remain <br />common with Lahontan redside predominant. Thus, the fish <br />community has been reduced from nine consistently occurring <br />species to five. Reservoir levels have fluctuated greatly, <br />eliminating the riparian zone in the lower stream section. In 13 <br />of the past 19 years, Stampede Reservoir has fallen below 50% <br />capacity and had an average annual change in volume of 32.1%. <br />These changes in the reservoir appear to have restructured the <br />upstream populations of fish. Two nearby streams similarly <br />influenced by a reservoir, have populations much like those in <br />Sagehen Creek. <br />57