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0 INTRODUCTION r The Colorado squawfish (Ptychocheilus lucius) was once widely distributed in the upper and lower Colorado River basins, but has been extirpated from 800 of its historic range (Tyus 1991a). Wild populations presently exist only in the Colorado, Green, Yampa, White, Gunnison, and San Juan rivers (Ryden and Pfeifer 1993) of the Upper Colorado River Basin (Holden and Wick 1982, Minckley and Deacon 1989). This fish was listed as an endangered species by the U.S. Fish and Wildlife Service (1974). Colorado squawfish in the White River represent a significant percent of the population in the Upper Colorado River Basin. Catch per unit effort (CPUE) of Colorado squawfish in the White River is about half that of the Green River and equal to that of the Yampa and Colorado Rivers (McAda et al. 1994). Earlier studies (Carlson et al. 1979, Miller et al. 1982, Martinez 1986) found that only adult and juvenile squawfish (>100 mm) (no larval or YOY squawfish < 100 mm have been collected in the river) use the White River and that adult fish migrate to spawning sites either in the Green and Yampa rivers. These squawfish also displayed home-range fidelity by returning to the White River following spawning (Miller et al. 1982, Martinez 1986, McAda et al. 1994). A comparison of successive studies on the White River (Lanigan and Berry 1981, Miller et al. 1982, Martinez 1986, Trammell 1991) provides documentation of a shift from predominately endemic to an exotic fish community in the lower reaches of the-White River, while endemic fishes remain the primary fish species in the upper reaches. The dominant exotic species are channel catfish (Ictalurus punctatus), common carp (Cyprinus carpio), fathead minnow (Pimephales promelas), and red shiner (Cyprinella lutrensis). It is unknown how these shifts in species composition affect the Colorado squawfish. The White River was impounded by Taylor Draw Dam in December 1984 creating Kenney Reservoir. This dam prevented access of Colorado squawfish to available habitat upstream of the dam and reduced the amount of historic home-range in the White River by 32% (Martinez 1986, Colorado River Fishes Recovery Team 1988, Trammell 1991). By restricting movement upstream of Taylor Draw Dam, many adult Colorado squawfish stockpiled at the base of the dam following spawning (Martinez 1986, Trammell 1991). Similar observations of squawfish congregating below river barriers were documented at Flaming Gorge Dam on the Green River (McDonald and Dotson 1960, Seethaler 1978) and Redlands Diversion on the Gunnison River (Miller et al. 1982, Burdick and Kaeding 1990). 0 1 0