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Colorado squawfish Adult Adult Colorado squawfish are widely distributed in the Yampa and Green rivers, where the fish is considered more abundant than in any other location (Holden and Stalnaker 1975; Tyus et al. 1982ab; Behnke and Benson 1983; Tyus, in press). In the mainstream Green River, adults were most prevalent in upper (near Ouray, Utah) and lower (near Labyrinth canyon) sections of low stream gradient (Tyus et al. 1987; Tyus and Haines 1991). During the winter, adult Colorado squawfish used a variety of Green River habitats, including in order of high to low use: slow runs, slackwaters, eddies, and backwaters (Valdez and Masslich 1989). In the unregulated Yampa River, the fish demonstrated a preference for off-channel backwater and embayment habitats that were judged sources of prey (Wick and Hawkins 1989). The fish selected certain river reaches in both rivers, remained in these reaches, and were generally active all winter (Valdez and Masslich 1989, Wick and Hawkins 1989). The fish presumably used ice as cover and flow fluctuations may have caused greater movement of Colorado squawfish than in more stable conditions (Valdez and Masslich 1989, Wick and Hawkins 1989). Movement of the fish into backwater habitats was attributed, in part, to winter feeding (Wick and Hawkins 1989). In spring and early summer, adult Colorado squawfish were most often located in seasonally inundated shorelines, including backwaters or bottomlands (Tyus 1990). Radiotracking data indicated use of shoreline backwater habitat in t-he 1981 low-flow year and use of flooded bottomlands during the 1983 high-flow year (Tyus and Karp 1989). Flooded shorelines were also used by adult Colorado squawfish during the two high-flow years, 1983 and 1984 (Tyus et al. 1987), and use of inundated portions of Old Charley Wash (a seasonally-flooded botto~) was noted from late April to May, 1985 and 1987, at flows of 226.4 - 283.0 m /s. Wick et al. (1983) noted that in 1982 (an average-flow year), adult Colorado squawfish used flooded shoreline areas in spring, but they moved to backwater habitats as the river level dropped. Adult Colorado squawfish occupied a variety of habitats in mid-to-late summer, but were most common in eddies, pools, runs, and shoreline backwaters, over sand and silt substrates (Tyus et al. 1984, 1987). Visual observations of fish in shallow water indicated that adults used sheltered microhabitats behind boulders, flooded vegetation, or other cover. Many of the radio-tagged fish were located in deeper shoreline habitats in the summer and their local movements in these habitats suggested heavy use of the eddy-run interface (Tyus et al. 1987). Capture of introduced northern pike Esox Lucius and channel catfish Ictalurus punctatus in habitats shared by adult Colorado squawfish (Wick et al. 1985; Tyus and Beard 1990) suggests a potential for competition and/or predation during times of resource limitation. Although Pimentel et al. (1985) found that Colorado squawfish did not prefer channel catfish as prey, observations of channel catfish lodged in throats of adult Colorado squawfish (McAda 1983; Pimentel et al. 1985; Wick et al. 1985) indicates that these 16