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Reducing negative impacts of non-native fishes is one of five elements of the Recovery Implementation Program Recovery Action Plan (RIPRAP). Section 2.3 of the. RIPRAP (USFWS 2000) indicates that, through 2003, emphasis be placed on nonnative fish removal and control activities. A project designed to control numbers of centrarchids and other large-bodied introduced fishes from Colorado River backwaters was conducted by USFWS from 1999-2001; this report summarizes results of this effort. Statement of Problem The Colorado River population of Colorado pikeminnow is comparatively small and numbers are currently limited by a low frequency of strong year classes (Osmundson and Burnham 1998). Reproduction may be limited by low egg hatching success during years of unfavorable environmental conditions (McAda and Ryel 1999). Larval and first- year survival may be limited in this and other rivers by high sustained flows during the period of drift (McAda and Rye] 1999), insufficient availability of optimal nursery habitat (Tyus and Haines 1991), slow growth resulting in increased winter mortality (Haines et al. 1998), and by predation in nursery habitats (Osmundson 1987, Ruppert et al. 1993, Nesler 2002). Offspring of stocked razorback sucker and bonytail may experience similar limiting factors. Predation by nonnative fishes is generally considered the greatest impediment to survival of larval razorback sucker in flooded bottomlands (Modde'et al. 2001). The most abundant fish predators that likely prey on native fish larvae include nonnative red shiners Cyprinella lutrensis (Rupert et al. 1993), sand shiners Notropis stramineus, and perhaps mosquitofish Gambusia affinis. As larvae grow in nursery habitats they quickly move out of a size range available to these small nonnative minnows and mosquitofish. However, Osmundson (1987) found that young-of-the-year (YOY) and yearling-sized Colorado pikeminnow remain highly susceptible to predation by introduced centrarchids, i.e., largemouth bass Micropterus salmoides, green sunfish Lepomis cyanella and black crappie Pomoxis nigromaculatus. In the upper Colorado River, largemouth bass and green sunfish are the most common, large, non-native, 2