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Draft Final Completion Report to UDWR for Contract #93-1070. Amendment 3 7 LIFE mSTORY AND HABITAT NEEDS OF LARVALCOLORADOSQUAWFffiH The life history of the Colorado squawfish has only been investigated since closure of the major dams in the Colorado River basin. Consequently, we only know what habitat is utilized in the altered, fragmented river system. This long-lived, large, endemic minnow was once widespread and abundant throughout the Colorado River basin. but is now found only in the upper Colorado basin. Within that basin. the largest known concentrations of squawfish are found in the Green River (Tyus and Haines, 1991). The Colorado squawfish has a complex life history and spawns on gravel bars in two canyon sections: Yampa Canyon on the Yampa River and Gray Canyon on the Green River. These fish migrate long distances (Tyus, 1990) and spawn on the descending limb of the spring snowmelt hydrograph, apparently cued by temperature (Tyus, 1990), After the eggs hatch, the larval fish are trarisported downstream for 3 to 15 days (Nesler and others, 1988). In the downstream reaches, the larval fish move or are entrained into 'backwaters" in low-gradient alluvial reaches. Backwaters, as described by aquatic ecologists, are areas of low or no velocity (McAda and Kaeding, 1989), and are most often embayments along river margins; these areas are the nursery habitat for age-O Colorado squawfish. The Green River, in the OurayNWR in the Uinta Basin. is an area of known Colorado squawfish nursery habitat (Tyus and Karp, 1991). Tyus and Haines (1991) found larval squawfish in embayments that were relatively warm, deep, and large in this reach. Crowl (1994, pers. comm.) has suggested that habitat depth partly determines habitat quality. Crowl has defined deep habitats as those with a depth greater than 0.5 m at any location within the habitat, and has noted that the deepest area is typically near the interface between flowing and low or no velocity zones. "