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<br />7 <br /> <br />ranged from 21.9' C to 27.6' C. The most preferred temperature for juveniles <br />and adults was estimated to be 24.6' C. Temperatures near 24' C are also <br />needed for optimal development and growth of young (Miller et al. 1982). <br /> <br />Most information on Colorado squawfish reproduction was gathered from spawning <br />sites on the lower 20 miles of the Yampa River and in Gray Canyon on the Green <br />River (Tyus et al. 1982; Tyus and McAda 1984; Tyus 1985; Wick et al 1985; Tyus <br />1990). Colorado squawfish spawn after the peak runoff season from June to <br />mid-August. Spawning begins when water temperatures reaches 180 to 250 C. and <br />peak spawning activity occurs between 220 to 250 C (Haynes et al. 1984; Archer <br />et al. 1985; Tyus 1990). During the decline in water level following peak <br />runoff. spawning adult fish move into run-riffle areas and occupy run, eddy, <br />and pool habitats (Tyus 1990). After spawning. adult Colorado squawfish <br />utilized a variety of riverine habitats including eddies, backwaters, <br />shorelines, and others (Tyus 1990). <br /> <br />Specific spawning sites of Colorado squawfish have not been identified outside <br />of the Green River basin. However. spawning has been confirmed by the <br />presence of larval squawfish in two reaches of the Colorado River: Black Rocks <br />to Loma, and Grand Junction to Clifton (McAda and Kaeding 1991). The presence <br />of larval squawfish aggregations and suitable spawning habitat in the Colorado <br />River near Cataract Canyon, Professor Valley, and upstream from the Dolores <br />River confluence indicate spawning is occurring in or near these areas as well <br />(Archer et al. 1985; Valdez 1990). <br /> <br />Data indicates that clean cobble substrates are necessary for spawning and <br />incubation (Tyus and Karp 1989). Several studies on the cobble cleaning <br />process have been conducted at a known spawning location in Yampa Canyon. <br />O'Brien (1984) studied the hydraulic and sediment transport dynamics of the <br />cobble bar within the Yampa River spawning site and duplicated some of its <br />characteristics in a laboratory flume study. O'Brien (1984) concluded that <br />incipient motion of the cobble bed is required to clean cobbles for spawning <br />and estimated that this takes discharges of about 21.500 cfs. However, Harvey <br />et al .(1993) concluded that since flows required for incipient motion of bed <br />material are rare (20 year return period event) and spawning occurs annually. <br />another process must be cleaning the cobbles. Their study found that in Yampa <br />Canyon recessional flows routinely dissect gravel bars and thereby produce <br />tertiary bars of clean cobble at the base of the riffles. These tertiary bars <br />are used by Colorado squawfish for spawning. Harvey et al. (1993) recognizes <br />the importance of high magnitude. low frequency discharges for the formation <br />and maintenance of midchannel bars Dissection of bars without redeposition <br />by high magnitude flows would lead to conditions where spawning habitat is no <br />longer available (Harvey et al. 1993). <br />