Abstract
Diversion (i.e. extraction) of water from rivers and estuaries can potentially affect native wildlife populations if operation is not carefully managed. For example, open, unmodified water diversions can act as a source of injury or mortality to resident or migratory fishes from entrainment and impingement, and can cause habitat degradation and fragmentation. Fish-protection devices, such as exclusion screens, louvres or sensory deterrents, can physically or behaviourally deter fish from approaching or being entrained into water diversions. However, empirical assessment of their efficacy is often lacking or is investigated only for particular economically or culturally important fishes, such as salmonids. The Southern population of anadromous green sturgeon (Acipenser medirostris) is listed as threatened in California, and there is a high density of water diversions located within their native range (the Sacramento-San Joaquin watershed). Coupled with their unique physiology and behaviour compared with many other fishes native to California, the green sturgeon is susceptible to entrainment into diversions and is an ideal species with which to study the efficacy of mitigation techniques. Therefore, we investigated juvenile green sturgeon (188-202 days post-hatch) in the presence of several fish-protection devices to assess behaviour and entrainment risk. Using a large experimental flume (∼500 kl), we found that compared with an open diversion pipe (control), the addition of a trash-rack box, louvre box, or perforated cylinder on the pipe inlet all significantly reduced the proportion of fish that were entrained through the pipe (P = 0.03, P = 0.028, and P = 0.028, respectively). Likewise, these devices decreased entrainment risk during a single movement past the pipe by between 60 and 96%. These fish-protection devices should decrease the risk of fish entrainment during water-diversion activities.
Highlights
Owing to the high density of water diversions in some locations (Herren and Kawasaki, 2001) and the large amount of water diverted from some river systems, entrainment into water diversions can pose a risk to several fishes, including those listed under the Endangered Species Act (ESA), such as delta smelt (Hypomesus transpacificus; Bennett, 2005) or green sturgeon (Acipenser medirostris; Mussen et al, 2014a)
Our results indicate that the tested fish-protection modifications of a water-diversion pipe can successfully reduce the entrainment risk of a threatened juvenile fish species while still maintaining water-diversion activities
Reconciliation between the needs of water diverters and native fish species is crucial for effective fish conservation and management, and our results suggest that such solutions are possible
Summary
Water diversions have been identified as a potential source of injury and mortality (Kimmerer, 2008; Baumgartner et al, 2009; Grimaldo et al, 2009), reduced fitness (Bennett, 2005; Kimmerer, 2008), or habitat degradation (Drinkwater and Frank, 1994; Kingsford, 2000) for many fish species. Mortality can be caused indirectly as a result of habitat fragmentation, degradation or alteration (Liermann et al, 2012; Sheer and Steel, 2006), or directly from interactions with water diversions and associated structures (Kimmerer, 2008). Examples of fish-protection devices include positive barriers, such as exclusion screens, and behavioural barriers, such as louvres or sensory deterrents. Positive barriers are designed to physically prevent a fish from being entrained into a water diversion (Taft, 2000; USBR, 2006), whereas sensory deterrents and louvres modify the behaviour of fish to deter interactions between the fish and the diversion (USBR, 2006; Noatch and Suski, 2012)
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