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Colorado and Little Colorado rivers in the Grand Canyon have collected over 21,000 specimens of adult and juvenile humpback chub since 1987 (Valdez 1991; Valdez et al. 1992; Douglas and Marsh 1992, 1993; Robinson and Clarkson 1992; Gorman et al. 1993; Arizona Game and Fish Department 1993). Specimens also have been collected from Shinumo, Bright Angel, Kanab and Havasu creeks (Maddux et al. 1987). Collections made in mainstem backwaters suggest that these habitats serve as important rearing areas for young-of-year humpback chub (Maddux et al. 1987). The cold tailwaters of the dam and fluctuating flows have apparently caused major reductions in both the distribution and abundance of humpback chub in Marble and Grand canyons (Minckley 1973; Holden and Stalnaker 1975a; Suttkus et al. 1976; Maddux et al. 1987). Humpback chub were collected in Lake Powell after closure of the dam in the 1960's (Holden and Stalnaker 1970; Suttkus and Clemmer 1977), but only young-of-year fish at the inflow area have been collected recently (Valdez 1987, 1988). In the Upper Basin, the highest known concentrations of humpback chub are found in the Black Rocks and Westwater Canyon reaches of the Colorado River near the Colorado/Utah State line (Valdez 1981; Wick et al. 1981; Valdez and Clemmer 1982; and Archer et al. 1985; Kaeding et al. 1990). A population of humpback chub has been reported from Cataract Canyon on the Colorado River above the inflow area to Lake Powell. A total of 108 humpback chub, of which 22 were adult fish and 56 were juvenile, were collected during a 4-year investigation of Cataract Canyon from 1985 to 1988, by Valdez (1990). These findings and those of past studies (Valdez et al. 1982b), indicate that there is a small population of humpback chub in Cataract Canyon. Although actual spawning has not been documented, the presence of various size humpback chubs, including possible young-of-year fish, through the 12-mile reach of Cataract Canyon supports the hypotheses that spawning occurs there. Specimens also have been collected from the Colorado River in Professor Valley above Moab, in Elephant Canyon about 2 miles above the confluence with the Green River, and in the inflow area of Lake Powell (unpublished U.S. Fish and Wildlife Service data; Valdez 1987, 1988). In December 1981, the Service stocked 7,600 age-I humpback chub, marked with a coded nose-tag, (progeny from Black Rocks) into Cataract Canyon, but no recaptures have been confirmed. Humpback chub were collected from the Desolation and Gray Canyons of the Green River in the early 1970's and 1979-81 (Holden and Stalnaker 1975a; Tyus et al. 1982b). The humpback chub also is rare in the Green and Yampa Rivers of Dinosaur National Monument (Holden and Stalnaker 1975a; Seethaler et al. 1979; Miller et al. 1982a). Tyus et al. (1987) reported that of 523 Gila sp. collected from the Green River basin during 1979-1986, humpback chub comprised 28 percent of those from the Green River and 12 percent of those from the Yampa River. Vanicek et al. (1970) indicated that the humpback chub was adversely affected in the Green River above the mouth of the Yampa River after Flaming Gorge Dam became operational in 1962. However, a spawning population remains in Yampa Canyon in Dinosaur National Monument near the confluence of the Green and Yampa rivers. A total of 32 fish in breeding condition were captured in Yampa Canyon from 1986-1988, including 5 ripe females, 14 ripe males, and 13 fish with breeding tubercles 27