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'" known. The largest populations of humpback chub occur in the Little Colorado and Colorado rivers in the Grand Canyon, and in the Black RockslWestwater Canyon area of the Colorado River. Other populations have been reported in Debeque and Cataract canyons of the Colorado River, Desolation and Gray canyons of the Green River, and Yampa and Whirlpool canyons in Dinosaur National Monument (USFWS 1990b). Populations of humpback chub are found in river canyons, where they utilize a variety of habitats, including pools, riffles, and eddies. Most of the existing information on habitat preferences has been obtained from adult fish in the Little Colorado River, the Grand Canyon, and the Black Rocks of the Colorado River (Holden and Stalnaker 1975; Kaeding and Zimmerman 1983; Kaeding et al, 1990). In these locations, the fish are found associated with boulder-strewn canyons, travertine dams, pools, and eddies. Some habitat-use data are also available from the Yampa River Canyon where the fish occupy similar habitats, but also use rocky runs, riffles, rapids, and shoreline eddies (Karp and Tyus 1990). This diversity in habitat use suggests that the adult fish is adapted to a variety of habitats, and studies of tagged fish indicated that they move between habitats, presumably in response to seasonal habitat changes and life history needs (Kaeding and Zimmerman 19~3; Karp and Tyus 1990). Reduced spring peak flows, availability of shoreline eddy and deep canyon habitats, and competition and predation by nonnative fishes were reported as potential limiting factors for humpback chub in the Yampa River (Tyus and Karp 1989). The impact of hybridization with other species is currently being evaluated. Humpback chub in reproductive condition are usually captured in May, June, and July, depending on location, Little is known about their specific spawning requirements, other than the fish spawn soon after the highest spring flows when water temperatures approach 680F (Karp and Tyus 1990; USFWS 1990b). The importance of spring flows and proper temperatures for humpback chub is stressed by Kaeding and Zimmerman (1983), who implicated flow reductions and low water temperatures in the Grand Canyon as factors curtailing successful spawning of the fish and increasing its competition with other species. Bonytail-- The bony tail is the rarest native fish in the Basin. Formerly reported as widespread and abundant in mainstream rivers (Jordan and Evermann 1896), its populations have been greatly reduced. The fish is presently represented in the wild by a low number of old adult fish (i.e., ages of 40 years or more) in Lake Mohave and perhaps other Lower Basin reservoirs (USFWS 1990a). The fish were once common in Lake Mohave vicinity where Wagner (1955) observed the fish in eddy habitats. A few individuals were reported in other locations, but concentrations of the fish have not been recently reported (Kaeding et al. 1986). The bony tail is adapted to mainstream rivers, where it has been observed in pools and eddies (Minckley 1973; Vanicek 1967). In reservoirs, the fish occupies a variety of habitat types (Minckley 1973), Spawning requirements have never been documented in a river, but Vanicek and Kramer (1969) reported that spawning occurred in June and July at water temperatures of about 640F. Although habitats that are required for conservation of the 16