Coho Survival and Stream Flow: How Much Water Do Coho Need in California Streams?

As part of an effort to monitor the effects of stream flow improvement projects on coho survival in small California streams, monthly oversummer survival of juvenile coho as a function of stream flow and other habitat metrics was evaluated. In June 2010, coho yoy were PIT tagged at the Don Clausen Warm Springs Fish Hatchery and released into six reference and treatment reaches in tributaries of the Russian River. In order to estimate monthly survival of stocked coho between June and November, a total of five paired “wanding” samples were completed on each reach using a portable PIT detection system. In order to obtain individually-based growth information, one electrofishing sample was conducted in October. Stationary PIT detection systems placed at the downstream end of each reach were used to document emigration from the study reaches throughout the period. Stream flow and temperature data were monitored continuously in or near each reach. Concurrent with wanding samples, habitat data (wetted area, average and maximum depth, dissolved oxygen, and instream cover rating) was collected monthly, for a total of five habitat surveys. Relationships between flow and oversummer survival are being used to develop target instream flows for each tributary and evaluate the long term effects of stream flow improvement projects on coho survival.