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disappear from these habitats by spring. It is very likely that these fish leave the river as the water temperatures decline and enter warmer inflow waters from riverside ponds and irrigation 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 river. The density of zooplankton needed for larval 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 identical patterns of resource utilization cannot coexist 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 7 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 Imaact on Fish-Eating 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 piscivorous birds 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). Mitchell (1995) identified 308 ponds -- 253 along the Colorado River with a total surface area of 721 acres and 61 along the Gunnison River with a total surface area of 197 acres. Mitchell reported that most of these ponds were less than 5 acres in surface area. The total number of 308 ponds includes the Upper Colorado River from the Colorado-Utah state line upstream to Palisade, Colorado. That number does not include numerous ponds that occur in the floodplain from Palisade upstream to Rifle, Colorado. There are numerous ponds along the Upper Colorado and Gunnison rivers that will serve as alternate feeding areas for fish-eating birds. Since nonnative fish would be removed from only a small proportion of the ponds in the project area i n any s i ngl a year (not more than 25 ponds or 8% of the 308 ponds identified by Mitchell (Martinez and Nesler 1996), many other ponds would still be available as alternate feeding areas. 19