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<br />IDENTIFICATION OF HABITAT REQUIREMENTS AND LIMITING <br /> <br />FACTORS FOR COLORADO SQUAWFISH AND HUMPBACK CHUB <br /> <br />Charles M. Haynes, Robert T. Muth, <br />and Thomas P. Nesler <br /> <br />ABSTRACT <br /> <br />Colorado squawfish reproduction appears restricted to reaches of the <br />mainstem Colorado River and lower Yampa River. The primary spawning area in <br />the Yampa for squawfish occurs in the lower 32-kg reach. Limited spawning <br />does occure above this reach. Flow and water temperature variables affect <br />overall success of Colorado squawfish spawning success between rivers and <br />within a given river on an annual basis. Spawning occurs in July through <br />August and coincides with decreasing flows and rising water temperatures at <br />or greater than 20 C. Peak spawning activity occurs in late July at mean <br />water temperatures of 22-25 C. Results from both rivers suggest an optimum <br />range of flows exists providing the best quantity and quality of spawning <br />habitat as well as an optimal number of degree days for egg incubation and <br />larval production. Dispersion of larval Colorado squawfish occurs via <br />downstream drift. No significant diel periodicity was apparent in the <br />drifting larvae. Juvenile squawfish were rarely collected in Yampa Canyon. <br />Under certain circumstances, reproductive success of native fish species in <br />the Yampa River appears enhanced relative to non-native species. Further <br />research recommendations are included. <br /> <br />oJ. <br />