Large-Scale River Simulations of an Unscreened Water Diversion Part 2: Behavior of Juvenile Anadromous Fishes and Implications for Successful Management and Conservation

Water projects designed to extract fresh water for local urban, industrial, and agricultural use worldwide have contributed to the fragmentation and degradation of suitable habitat for native fish, and present challenges to successful fish passage around such devices. In the Sacramento-San Joaquin watershed of California, the number of water diversions exceeds 3,300, and the majority of these remain unscreened. Many juvenile anadromous fish species are susceptible to entrainment into these diversions, which may affect populations of native fish species already in decline. Therefore we tested the efficacy of a sensory deterrent (strobe light) and several structural pipe modifications (upturned pipe configuration, altered pipe plate, trash rack box, louver box, and perforated cylinder cap) in reducing the entrainment of juvenile green sturgeon (Acipenser medirostris) and juvenile Chinook salmon (Oncorhynchus tshawytscha) in a large-scale river simulation flume over several years. The structural pipe modifications were largely successful in significantly reducing fish entrainment rates for both species, though species-specific behavioral differences were observed. Our results are informative in developing effective management strategies to mitigate the impacts of water diversions for specific species, and suggest that effective restoration strategies that balance agricultural needs with conservation programs are possible.