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1989). The fish presumably used ice as cover, and they moved to avoid floating <br />ice jams (Valdez and Masslich 1989). <br />Flow fluctuations in the winter may affect preferred winter habitats, and <br />movement patterns suggested that such fluctuations resulted in greater <br />movement of Colorado squawfish than in more stable conditions (Valdez and <br />Masslich 1989, Wick and Hawkins 1989). Fluctuation in river level greater than <br />5cm/h caused 190% more movement in adult Colorado squawfish in the Green River <br />120m downstream of Flaming Gorge Dam (Valdez and Masslich 1989). <br />In spring and early summer, adult Colorado squawfish were most often <br />located in inundated shorelines, including backwaters or bottomlands (Tyus, in <br />review). Radiotracking data indicated use of shoreline backwater habitat in <br />the 1981 low-flow year and use of flooded bottomlands during the 1983 high- <br />flow year (Tyus and Karp 1989). Flooded shorelines were also used by adult <br />Colorado squawfish during the two high-flow years, 1983 and 1984 (Tyus et al. <br />1987), and use of inundated portions of Old Charley Wa~h was noted from late <br />April to May, 1985 and 1987, at flows of 226.4 - 283 m /s. Wick et al. (1983) <br />noted that in 1982 (an average-flow year), adult.Colorado squawfish used <br />flooded shoreline areas in spring but moved to backwater habitats as the river <br />level dropped. <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 <br />of fish in shallow water indicated that adults used sheltered microhabitats <br />behind boulders, flooded vegetation, or other cover. During the summer, <br />radio-tagged fish were most often located in deeper shoreline habitats where <br />movements suggested heavy use of eddy-run interface (Tyus et al. 1987). <br />Capture of introduced northern pike Esox Lucius and channel catfish <br />Ictalurus punctatus in habitats shared by adult Colorado squawfish (Wick et <br />al. 1985; Tyus and Beard 1990) suggests a potential for competition and/or <br />predation during times of resource limitation. Although Pimental et al. (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 1983, Pimental et al. 1985, Wick et al. 1985) indicates that these <br />introduced fish are eaten by Colorado squawfish, and may cause mortality. <br />Conditions favorable for non-native fishes that may compete with (or other <br />adverse interactions) Colorado squawfish should be avoided. Species of concern <br />include channel catfish, northern pike, and walleye Stizostedion vitreum. <br />Migration <br />The initiation of spawning migration is an important component of the <br />reproductive cycle of the Colorado squawfish. Based on radiotracking data <br />(Wick et al. 1983; Tyus and McAda 1984; Tyus 1985, in review), fish in both <br />Green and Yampa rivers initiated spawning migrations around the Summer <br />Solstice; Green River fish initiated migrations about June 21 (range: May 23 <br />to July 27) and Yampa River fish migrated about June 19 (range: May 27-July <br />12; Figure 4): These migrations included downstream movements in the Yampa and <br />White rivers and upstream and downstream movements in the Green River (Tyus et <br />al. 1987; Tyus, in review). Flows and water temperatures were highly variable <br />within each migration period and among years. However, spawning migrations <br />were initiated earlier in low-water years (e.g., 1981) and later in higher <br />water years, e.g., 1983. Spawning migrations of radio-tagged Colorado <br />squawfish were associated with highest spring flows and river temperatures <br />16 <br />