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000587 demonstrated that one 12-inch largemouth bass has the predatory effect of 200 redside shiners (Notroois lutrensis) (Appendix D of Martinez 1996). Osmundson (1986) reported that small squawfish were consumed more readily than larger ones by largemouth bass; Immediately after stocking Colorado squawfish in riverside ponds along the Upper.Colorado River, largemouth bass completely switched their diets to squawfish that Osmundson related to prey abundance and vulnerability since the squawfish were in a strange environment and were probably stressed from handling prior to stocking. Largemouth bass are not numerous in the riverine habitat of the Colorado Ri ver but occupy the qui et backwater areas that are used by 1 arva 1 and juvenile endangered fishes (Miller et ale 1982; Tyus et ale 1982; Valdez et ale 1982). D. Osmundson (1994, Personal Communication) stated that young largemouth bass are commonly found in backwater habitats in late summer but disappear from these habitats by spring. It is very likely that these fish 1 eave the ri ver as the water temperatures decl i ne' and enter warmer i nfl ow waters from ri vers i de ponds and i rri gat i on return ditches. Each summer young largemouth bass reappear in the Colorado River, suggesting chronic escapement of this species is a continual problem. The potential for competition between small largemouth bass and juvenile endangered fishes also exists because these fish feed on small organisms such as zooplankton, feed more intensely at warmer water temperatures, and occupy the same quiet habitats such as backwaters and embayments along the ri ver. The dens ity of zooplankton needed for 1 arva 1 razorback sucker survival is about 20 organisms per liter of water (Papoulias and Minckley 1990). However, that density is only occasionally reached for brief periods of time in backwaters (late summer) and never reached in the river (Cooper and Severn 1994 a, b, c, d; Grabowski and Hiebert 1989; Mabey and Schiozawa 1993). The competitive exclusion principle states that two or more species with ident i ca 1 patterns of resource utili zat i on cannot coexi st without competition (Hardin 1960). . Seventy-six percent of 26 fishery biologists and managers who were familiar with the Colorado River system identified nonnative fishes as a problem to native fishes in response to a questionnaire prepared by Hawkins and Nesler (1991). Largemouth bass was ranked number? among 28 nonnative fish species considered to be a problem to native fishes in the Colorado River system. Channel catfish were ranked number 1 and red shiner was ranked number 2. Predation by ictalurid catfishes prevented the re-establishment of stocked razorback suckers in the Lower Colorado River (Marsh and Brooks 1989). Potential Imoact on Fish-Eatinq Birds. Ponds in which the nonnative fishes were removed would not be useful as feeding areas to some birds that use fish as a major part of their diets. Birds that feed on other food organisms would not be affected by removal of nonnative fishes. However, most pi sci vorous bi rds that occur in the, project area are not abundant (Appendix B; NOTE: some of the gulls and terns that occur very rarely or accidentially in the project area are not included in Appendix B; Appendix A provides a checklist of all bird species that have been observed in the project area). 18