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catfish may have occurred. In addition, Coon (1965) reported channel catfish predation on Colorado squawfish in the Dolores River. Humpback Chub Humpback chub occur in several canyon-bound, white-water sections of the Green River basin, including the lower portion of the Little Snake River and Yampa, Whirlpool, Desolation and Gray canyons {Holden 1978; Tyus et al. 1982ab, 1987; Karp and Tyus, in review;- M. Moretti and E. Wick, pers. comm.). Survey studies conducted prior to and following closure of Flaming Gorge Dam indicated that all three forms of Colorado chubs were l.ocaliy common in the Green River; bonytails and roundtails in upper Green River above Ouray, Utah; humpbacks in Desolation and Gray canyons and historically in Flaming Gorge basin of upper Green River (Smith 1960; Hoiden 1978; Vanicek 1967; Seetha]er et al. 1979). Although intensive netting and electrofishing efforts in the Green River mainstream by USFWS and Utah Division of Wildlife Resources biologists yielded over 500 chubs (Min er et al. 1982; Tyus et al, 1987; M. Moretti, pers. comm.), status of humpback chub in that system is not well understood, due in part, to confusion with specific identification of some individuals {Tyus et al. 1987, M. Moretti, pers. comm.).- During the spring and early summer, adu]t humpback chub were most often collected in shoreline eddy habitats created by large boulders and rapids (Karp and Tyus, in review). Juvenile fish were most prevalent in smaller eddies in shoreline runs. Humpback chub were observed to feed at various levels within the water column, consuming such terrestrial insects as ants and Mormon crickets-{Tyus and Hinckley 1988; Karp and Tyus, in review). There is some indication that humpback chubs in Yampa Canyon exhibit short-distance, localized movements, and display some fidelity to specific eddy habitats (Karp and Tyus, in review). Adult humpback chub were captured in DNM in association with 18 other fishes, but were most commonly captured with roundtail chub and the introduced channel catfish-(Tyus and Hinckley 1988; Karp and Tyus, in review). Channel catfish comprised about 35% of the angling catch in habitats from which humpback chub were collected (Karp and Tyus, in review) and humpback chub and channel catfish may be competing for food or microhabitat as suggested by capture of both species with baits in the same eddy habitats (Tyus and Hinckley 1988; Karp and Tyus, in review). The high number of channel catfish in humpback chub spawning habitat, in addition to their potential ability to compete and prey on humpback chub (Kaeding and Zimmerman 1983; Karp and Tyus, in review; C. 0. Hinckley, personal communication), suggests that this omnivorous introduced species may adversely affect survival of humpback chub in DNM.- Channel catfish may be using mainstream habitats in the Green River for winter refugia as in some other river systems (Newcomb 1989). Flows or other conditions (e.g. temperature and fish movements) which may favor growth and reproduction of channel catfish in the Green River basin should be evaluated. Humpback chub in DNM spawn following highest spring flows at river temperatures about 20° C (Figure 7; Karp and Tyus, in review). This relationship between chub spawning and spring runoff has also been noted in the Blackrocks area of the upper Colorado River (Valdez and Clemmer 1982; Archer et al. 1985), and. in the Little Colorado River, Ariz. (Kaeding and Zimmerman 1983; C.O. Hinckley, pers. comm.). Spring runoff is important to reproductive success because spawning presumably occurs in shoreline eddies, 21