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<br />Colorado squawfish <br /> <br />Adult <br /> <br />Adult Colorado squawfish are widely distributed in the Yampa and Green <br />rivers, where the fish is considered more abundant than in any other location <br />(Holden and Stalnaker 1975; Tyus et al. 1982ab; Behnke and Benson 1983; Tyus, <br />in press). In the mainstream Green River, adults were most prevalent in upper <br />{near Ouray, Utah} and lower {near labyrinth canyon} sections of low stream <br />gradient {Tyus et a1. 1987; Tyus and Haines 1991}. <br /> <br />During the winter, adult Colorado squawfish used a variety of Green River <br />habitats, including in order of high to low use: slow runs, slackwaters, <br />eddies, and backwaters (Valdez and Masslich 19B9). In the unregulated Yampa <br />River, the fish demonstrated a preference for off-channel backwater and <br />embayment habitats that were judged sources of prey (Wick and Hawkins 1989). <br />The fish selected certain river reaches in both rivers, remained in these <br />reaches, and were generally active all winter (Valdez and Masslich 1989, Wick <br />and Hawkins 1989). The fish presumably used ice as cover and flow fluctuations <br />may have caused greater movement of Colorado squawfish than in more stable <br />conditions (Valdez and Masslich 1989, Wick and Hawkins 1989). Movement of the <br />fish into backwater habitats was attributed, in part, to winter feeding {Wick <br />and Hawkins 19B9}. <br /> <br />In spring and early summer, adult Colorado squawfish were most often <br />located in seasonally inundated shorelines, including backwaters or <br />bottomlands (Tyus 1990). Radiotracking data indicated use of shoreline <br />backwater habitat in the 1981 low-flow year and use of flooded bottom1ands <br />during the 19B3 high-flow year (Tyus and Karp 1989). Flooded shorelines were <br />also used by adult Colorado squawfish during the two high-flow years, 1983 and <br />19B4 (Tyus et a1. 1987), and use of inundated portions of Old Charley Wash (a <br />seasonally-flooded botto~) was noted from late April to May, 1985 and 1987, at <br />flows of 226.4 - 2B3.0 m Is. Wick et al. (1983) noted that in 1982 (an <br />average-flow year), adult Colorado squawfish used flooded shoreline areas in <br />spring, but they moved to backwater habitats as the river level dropped. <br /> <br />Adult Colorado squawfish occupied a variety of habitats in mid-to-late <br />summer, but were most common in eddies, pools, runs, and shoreline backwaters, <br />over sand and silt substrates (Tyus et al. 1984, 1987). Visual observations of <br />fish in shallow water indicated that adults used sheltered microhabitats <br />behind boulders, flooded vegetation, or other cover. Many of the radio-tagged <br />fish were located in deeper shoreline habitats in the summer and their local <br />movements in these habitats suggested heavy use of the eddy-run interface <br />(Tyus et al. 1987). <br /> <br />Capture of introduced northern pike Esox lucius and channel catfish <br />Ictalurus Dunctatus in habitats shared by adult Colorado squawfish (Wick et <br />a1. 1985; Tyus and Beard 1990) suggests a potential for competition and/or <br />predation during times of resource limitation. Although Pimentel et a1. (1985) <br />found that Colorado squawfish did not prefer channel catfish as prey, <br />observations of channel catfish lodged in throats of adult Colorado squawfish <br />{McAda 19B3; Pimentel et al. 1985; Wick et a1. 1985} indicates that these <br /> <br />16 <br />