Upstream Changes in Native Fish Abundance After Reservoir Impoundment in California Streams of the Lahontan Basin

MASTERS THESIS: Native fish population surveys were conducted in five California streams of the Truckee River system in the western Lahontan Basin in July and August, 1987. Areas sampled were above impoundments in four streams and below an impoundment in Martis Creek. Results were compared to surveys both before and after stream impoundment. Native fishes were virtually absent in Martis creek and scarce in the Little Truckee River. Compared to 1982-83 surveys, fish numbers increased measurably in both Sagehen Creek and Prosser Creek, exhibiting a measure of persistence and resilience to disturbance. However, in Sagehen Creek, the increased fish abundance was limited to two native species and an area normally inundated by the reservoir. Although, Alder Creek and Prosser Creek supported sizable populations of mountain sucker (Catostomus platyrhynchus) and Lahontan speckled dace (Rhinichythys osculus robustus) in portions of their lower sections, mountain sucker, Lahontan speckled dace, and mountain whitefish (Prosopium williamsoni) were generally scarce throughout the five streams. Stream impoundments are suspected of creating conditions leading to the extinction of mountain sucker, Lahontan speckled dace, and mountain whitefish in upstream areas. Principal reasons are loss of habitat, greater environmental variability from fluctuating reservoir levels, and increased barriers to migration.