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<br />liG2499 <br /> <br />among fisheries managers and have been reviewed elsewhere, the remainder of this <br />review will focus attention on special considerations for main channels and more exotic <br />techniques. <br /> <br />Fish passage, diversion, salvage, and removal facilities have been in place in <br />various locations across the country for many years. These facilities are operated by <br />public and private agencies, and usually have been constructed in an effort to reduce <br />the loss of fish drawn into intakes for irrigation canals, power generation facilities and <br />the likes (Bates 1995; USOTA 1995). One example with characteristics that might be <br />suitable for the UCRB is a fish salvage project operated jointly by the US Bureau of <br />Reclamation (USBR) and the State of California near the town of Tracy in the Central <br />Valley (USBR 1985, California Dept. of Water Resources 1991). One facility was <br />constructed in the 1950s and a second in the 1970s for the purpose of reducing the <br />loss of fish (primarily striped bass and chinook salmon) when water is pumped from the <br />Sacramento-San Joaquin River delta. A louver system separates fish from the intake <br />water and the fish are transported to another location. The system takes advantage of <br />fish movement in a manner that could be applied in the UCRB. Nonnatives could be <br />separated from natives and the non natives could be relocated or destroyed. <br /> <br />Barriers can prevent fish movements permanently or selectively. The <br />effectiveness of a barrier depends on a thorough knowledge of the behavior (e.g., <br />dispersal, migration, home range movements) of both target and beneficiary species. <br />Physical structures and electrical devices have been used to block fish movement at <br />various locations in the Colorado River system. For example, the Arizona Game and <br />Fish Department operates the Granite Reef Electric Fish Barrier on the Arizona Canal <br />in the Salt River drainage (Wright and Sorenson 1995). Barriers could be used <br />permanently or seasonally to prevent nonnative fishes from entering high priority <br />habitat such as spawning areas or special recovery areas. <br /> <br />One scenario for a long-term control effort could be based on increased <br />exploitation of channel catfish. The channel catfish is a predator that poses a serious <br />threat to the endangered big river fishes of the UCRB. It is abundant and is able to <br />reproduce in the riverine environment; complete eradication is not a realistic goal. The <br />best a control strategy can anticipate for this species would be to minimize its negative <br />impacts on the native fishes. This can be accomplished by focusing effort on the larger <br />channel catfish, which are more likely to be piscivorous. Hill et al. (1995) found that <br />channel catfish in South Dakota did not become highly piscivorous until they exceed <br />400 mm, at which time the relative importance of fish in the diet increased 25 times or <br />more relative to that of smaller fish. Similar results were obtained by Tyus and Nikirk <br />(1990) in the Green River basin. Although the size threshold for predominant piscivory <br />may vary among river systems (Zurlin 1982), larger catfish still consumed more fish. <br />Reduction in the abundance and size of channel catfish should aid the native fish <br />communities by reducing predation risk, <br /> <br />22 <br />