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<br />T~ <br />""'> <br /> <br />/t1:\ <br />'-'ii) <br /> <br />11 <br /> <br />River Basin, Colorado squawfish occurred in the Colorado, Green, Yampa, White, <br />Dolores, Gunnison, San Juan, Uncomphagre, and Animas Rivers, and in many <br />smaller tributaries. Although still occurring in much of its former upper <br />basin range, most areas contain only remnants of their former number and few <br />reproducing populations exist. <br /> <br />All life-history phases of the Colorado squawfish are considered in this <br />biological opinion and include migration, spawning, and larval recruitment to <br />the adult life-stage. These phases are closely related with specific flow <br />events and habitat requirements. The recovery goals for Colorado squawfish <br />establ ished through the Recovery Program are to "maintain and protect self- <br />sustaining populations and natural habitat." <br /> <br />Adults <br /> <br />Adult Colorado squawfish are widely distributed in the Yampa and Green Rivers, <br />and the fish is considered more abundant in the Green River than any other <br />location (Holden and Stalnaker 1975; Tyus et al. 1982a and 1982b; Behnke and <br />Benson 1983; Tyus, in press). In the mainstream Green River, adults are most <br />prevalent in upper (i.e., near Ouray, Utah) and lower (i.e., near Labyrinth <br />canyon) sections (Tyus et al. 1987). <br /> <br />During the winter months, adult Colorado squawfish occupy a variety of low <br />velocity habitats including slow runs, slackwaters, eddies, and backwaters <br />(ephemeral along-shore embayments)(Valdez and Masslich 1989; Wick and Hawkins <br />1989). Colorado squawfish select certain river reaches in the Green and upper <br />Yampa Rivers and generally remain active in these areas all winter (Valdez and <br />Masslich 1989, Wick and Hawkins 1989). The fish presumably use ice as cover <br />and some local movements are probably made to avoid floating ice jams (Valdez <br />and Masslich 1989). <br /> <br />Flow fluctuations in the winter may effect fish use of preferred winter <br />habitats. Movement patterns of radiotagged fish suggested that such <br />fluctuations result in greater movement of Colorado squawfish than in more <br />stable conditions (Valdez and Masslich 1989; Wick and Hawkins 1989). Valdez <br />and Masslich (1989) believed that a rapid change in river stage altered <br />l6cations of squawfish preferred microhabitats resulting in greater fish <br />movement. Increased movement was hypothesized as resulting in increased <br />energy expenditure and decreased body condition. Decreases in body condition <br />during winter may effect ova development, number, and size. <br /> <br />In spring and early summer, adult Colorado squawfish are most often located in <br />seasonally inundated shoreline habitats, including backwaters or bottomlands <br />(Tyus 1990). Radiotracking data indicated use of shoreline backwater habitat <br />in the 1981 low-flow year and use of flooded bottomlands during the 1983 high- <br />flow year (Tyus and Karp 1989). During the two high-flow years, 1983 and <br />