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INTRODUCTION Introduced fishes in the Upper Colorado River Basin (UCRB) have become more widespread and abundant while the native big river fishes have disappeared from about three-fourths of their origi~i habitat (Tyus and Saunders 1996). In areas that have bad little alteration to the physical habitat, nonnative fish abundance has increased while the abundance of natives has been reduced. • Suitabfiity of the physical habitat is an important requirement for the native fish. However, most suitable habitat is now occupied by introduced species, many of which are predacious, highly competitive, and harmful to the native fish fauna (Hinkley 1982, Tyus et aL 1982, Carlson and Muth 1989). The UCRB fish community is currently made up of approximately 42 nonnative species relative to the remaining 13 native species. Competition and predation by nonnatives are ~ believed to be a significant cause of poor recruitment and low abundance of native fish of fire UCRB (Tyus et al. 1982, Kaeding and Osmundson 1988, Marsh and Brooks 1989). The UCRB Recovery Program has increased its emphasis on studying specific interactions with select nonnative species in controlled experiments. Several nonnative fishes, including green ~ sunfish, common carp, aad channel catfish, have been observed feeding on eggs and/or larval razorback suckers (Langhorst 1989, Marsh and Brooks 1989). Hawkins and Nesler (1991) identified six species of nonnative fishes which were of greatest concern to UCRB researchers due to their potential inopacts on native fishes. Among these species were: red shiner (Cyprinella lutrensis), common carp (Cyprinus carpio), fathead minnow (Pimephales promelas), channel catfish (Ictalurus punctatus), northern pdce (Esox luciats), and green sunfish (Lepomis cyanellus). • Researchers at the normative workshop held in Boulder, Colorado in 1995, found channel catfish as being the greatest threat to the endangered fish community. Additionally, two priority areas for nonnative fish control were identified in the UCRB: the Colorado River from the Grand Valley Diversion to the confluence with the Green River, and the Green River from Split Mountain to Desolation Canyon. Due to increasing concerns of researchers, maay nonnative removal projects • have been established in the Colorado River Basin since 1995, inchuding channel catfish removal efforts in the Yampa and San Juan rivers, and nonnative cyprinid removal projects in Colorado and Utah on the Colorado and Green rivers. Within the Green River, smallmouth bass (Micropterus salmoides) have maintained themselves • near the confluence with the Duchesne River. The source is aself-sustaining population in the lower reaches of the Uinta River (I.entsch et a1.1996). This sport fishery was established in i 970 and was the first documented successful smallmouth bass population in the UCRB. Additionally, Starvation Reservoir on the Duchesne River is known to be a source of smallmouth bass (Kevin Christopherson, pers. comm.). Colorado River Basin (CRB) researchers ranked smallmouth bass • tenth on a list of 28 nonnative fish species considered to adversely impact native fishes of the CRB and the southwestern United States (I,entsch et a1.1996). Additionally, Hawkins and Nesler 1991, suspected impacts of smallmouth bass predation on young of native fishes of the Gila. River Basin. Channel catfish were first introduced to Utah circa 1888, found their way into the UCRB in 1892, • and proliferated rapidly through the early 1900's (Holden and Stahlaker 1975, Tyus and Nikirk 1990). Their current status of abundant to common throughout the basin confirms the ability of these fish to persist in this region. However, the life history characteristics of channel catfish in this system are different from these fish in their native range. Growth rates of chancel catfish in •