Distribution, Abundance, Growth, and Habitat Use of Steelhead in Uvas Creek, CA

Distribution, abundance, growth, and habitat use of juvenile steelhead (Onorhynchus mykiss) were studied in a central California stream under two increased summer flow reservoir release strategies. The effect of habitat quality (including longitudinal changes in flow, water temperature, canopy closure, substrate quality, and turbidity) on abundance and growth of steelhead among sites was determined. Increased stream flow extended rearing habitat and steelhead distribution downstream to reaches that previously would have been dry. Yearling or older steelhead were relatively scarce at all Uvas Creek sites. Steelhead were most abundant, but small, in the upstream half of the study reach, despite higher flows and cooler water for most of the summer. Insects were scarce at upstream sites due to dense shade, silty substrate, and high turbidity in late summer and fall. Steelhead grew much larger at warmer downstream sites, and reached smolt size by their first winter. Downstream sites were productive due to less shade, better substrate quality, and low turbidity. Steelhead abundance in the downstream reach was limited by the scarcity of fast-water feeding habitat. These results show that, where food is sufficient, steelhead can rear and reach smolt size in their first year in warm, augmented stream flows. Management strategies that improve stream productivity would improve steelhead production in Uvas Creek below the reservoir