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19 Temperature also affects egg development and hatching. In the laboratory, egg mortality was 100 percent in a controlled test at 13° C. At 13° to 18° C, development of the egg is slightly retarded, but hatching success and survival of larvae was higher. At 20° to 26° C, development and survival through the larval stage was up to 59 percent (Hamman 1981). Juvenile temperature preference tests showed that preferred temperatures ranged from 21.9°~to 27.6° C. The most preferred temperature for juveniles and adults was estimated to be 24.6° C. Temperatures near 24° C also are needed for optimal development and growth of young (Miller et ai. 1982). Most information on Colorado squawfish reproduction was gathered from spawning sites on the lower 20 miles of the Yampa River and in Gray Canyon on the Green River (Tyus et al. 1984, Tyus and McAda 1984, Tyus 1985, Wick et al. 1985, Tyus 1990). Colorado squawfish spawn after the peak runoff season from June to September. Spawning begins when water temperatures reaches 18° to 25° C, and peak spawning activity occurs between 22° to 25° C (Haynes et al. 1984, Archer et al. 1986, Tyus 1990). During the decline in water level following peak runoff, spawning adult fish move into run-riffle areas and occupy run, eddy, and pool habitats (Tyus 1990). After spawning, adult Colorado squawfish utilized a variety of riverine habitats including eddies, backwaters, shorelines, and others (Tyus 1990). Specific spawning sites of Colorado squawfish have not been identified outside of the Green River basin. However, spawning has been confirmed by the presence of larval squawfish in two reaches of the Colorado River: Black Rocks to Loma, and Grand. Junction to Clifton (McAda and Kaeding 1991). Larval Colorado squawfish also have been collected both upstream and downstream of Redlands Diversion Dam (Burdick 1997). The presence of larval squawfish aggregations and suitable spawning habitat in the Colorado River near Cataract Canyon, Professor Valley, and upstream from the Dolores River confluence indicate spawning is occurring in or near these areas as well (Archer et al. 1986, Valdez 1990). , Data indicate that clean cobble substrates are necessary for spawning and incubation (Tyus and Karp 1989). Substrates are swept clean of finer sediments by high flows scouring the bed prior to the spawning period. O'Brien (1984) studied the hydraulic and sediment transport dynamics of the cobble bar within the Yampa River spawning site and duplicated some of its characteristics in a laboratory flume study. Based on field observations, he reported: "On the rising limb of the hydrograph, sands are deposited in the cobble interstices. These sands are interchanged between the bed and