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Migrations were initiated from May 12 to June 10, associated with a mean water temperature <br />of about 57°F, and spawning occurred at 70°F (Tyus and Karp 1989). However, Wick et <br />al. (1985) and Tyus et al. (1987) cautioned that main channel temperatures may not <br />accurately portray temperature preferences of Colorado squawfish because the species <br />frequently utilized habitats outside the main river channel, such as large backwaters, gravel <br />pits, and flooded bottomlands, which may be influenced more by ambient air temperatures <br />and solar radiation. <br />Radiotelemetry studies of Colorado squawfish in the Green River basin indicate that <br />spawning is concentrated in two major sites: (1) the lower 20 miles of Yampa River canyon; <br />and (2) Gray Canyon of the Green River (Tyus et al. 1984; Tyus and MCAda 1984; Tyus <br />1985; Wick et al 1985; Tyus 1990). Spawning also is suspected in Labyrinth Canyon in the <br />Green River about 31.25 miles upstream of the Colorado River confluence (Tyus et al. <br />1987). This is supported by the capture of many young larval fish (protolarvae) immediately <br />downstream of this reach (Valdez 1990). Collections made on the two known spawning <br />grounds during 1981-88 produced 308 Colorado squawfish, of which 208 were ripe and an <br />additional 67 fish showed secondary sex characteristics associated with breeding condition <br />(Tyus 1990). Four fish tagged in the White River were recaptured at the Yampa and Gray <br />Canyons spawning areas, and the recapture of five fish tagged and recaptured in the Yampa <br />River spawning grounds after 2 or more years indicated a fidelity to that area (Tyus 1985, <br />1990). <br />The Yampa spawning population is considered historical. Holden and Stalnaker (1975b) <br />reported increased numbers of ripe Colorado squawfish in the lower Yampa River in July <br />1968-70, and Seethaler (1978) reported ripe fish there in 1974-75. Successful reproduction <br />in the lower Yampa River was substantiated when larval Colorado squawfish were collected <br />in the lower 30 miles and below its confluence with the Green River from 1980-83 (Haynes <br />et al. 1984; Tyus et al. 1987). <br />Gray Canyon of the Green River was suspected as a spawning site in 1981 when a <br />radio-implanted Colorado squawfish from the White River was tracked to that location (Tyus <br />et al. 1982b; Radant et al. 1983). Spawning was confirmed there by additional data collected <br />in 1983 (Tyus 1985). Additional Colorado squawfish have been tracked to Gray Canyon, <br />and 111 ripe fish were collected there in 1981-88 (Tyus 1990). <br />Two reaches of the Colorado River contain spawning areas; Black Rocks to Loma and Grand <br />Junction to Clifton (McAda and Kaeding 1991). Additionally, the presence of larval <br />squawfish aggregations and suitable spawning habitat in the Colorado River near Cataract <br />Canyon, Professor Valley, and upstream from the Dolores River confluence indicate <br />spawning is occurring in or near these areas as well (Archer et al. 1985; Valdez 1990). <br />21