Abundance and survival of common benthic biota in a river affected by water diversion during an historic drought

Abstract

Hydrologic changes, such as drought or managed flow, can influence the abundance and survival of aquatic biota. The purpose of this research is to understand the effects of naturally low streamflows coupled with water withdrawals on an abundant net-spinning caddisfly (Hydropsychidae) and a common benthic darter (Percidae). Results show that caddisfly production was lower than in a previous study and that larvae preferred habitats vulnerable to periodic exposure from water withdrawals, likely leading to the observed decline in abundance and production. Using capture-recapture methods, fish were estimated to be abundant with considerable site fidelity; estimated survival rates were lower for young-of-year fish compared to adult fish. Results from this study allow for future comparisons of fish population responses to interannual changes in streamflow. The coupling of natural drought and human-induced flow alterations provided a unique opportunity to study flow-ecology linkages in a sixth-order flow-altered stream.