Longitudinal movement of fish in response to a single-day flow pulse

We studied whether fish were displaced longitudinally downstream by a 1-day whitewater kayaking pulse flow release from Camino Dam on Silver Creek, a tributary of the South Fork American River, California. On 15 September 2004 flows were increased from a base flow of 0.48 m(3).s(-1) to a peak of 18.48 m(3).s(-1) by midday, and decreased back to base levels. Rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) were observed in snorkel surveys before and after the pulse. Counts of young-of-the-year and juvenile trout were 26% and 9% lower after the pulse, respectively. Counts of adult trout were 12% higher. Six adult trout were radio-tagged and were observed in the reach before, during, and after the pulsed flow. Our results suggest that most trout were able to remain in the study reach during the pulse, but that smaller fish may be more likely to be displaced downstream.