Laserfiche WebLink
Colorado squawfish Ptychocheilus Lucius, the largest North American <br />minnow, is endemic to the Colorado River basin where it was once abundant <br />and widely distributed (Jordan and Evermann 1896). The species was <br />classified as federally endangered by the U.S. Fish and Wildlife Service <br />in 1967 (Federal Register 32[43]:4001) and natural populations presently <br />exist only in the upper Colorado River basin (upstream of Lee Ferry, <br />Arizona). The Green River in Utah and its largest tributary, the Yampa <br />River in Colorado (Figure 1), contain the largest known concentration of <br />Colorado squawfish (Holden and Wick 1982; Tyus 1990). <br />Two major spawning areas have been identified in the Green River basin <br />by radiotracking migrations of Colorado squawfish, capture of ripe adults <br />and emergence of newly hatched fry. One spawning area in the lower Yampa <br />River (i.e., Yampa Canyon) was located in 1981 (Tyus and McAda 1984), and <br />a second spawning area in Gray Canyon of the Green River was located in <br />1983 (Tyus 1985]. Other spawning areas have not been confirmed after many <br />years of study. Successful Colorado squawfish reproduction was confirmed <br />at the Yampa Canyon site by collections of newly-hatched larvae (Haynes et <br />al. 1984; Nesler, 1988). However, early life history and ecology of larval <br />and postlarval Colorado squawfish are not well known. Events during the <br />first year of life regulate many fish populations (Braum 1978), and a <br />better understanding of such events aid in recovery efforts for this <br />species. <br />Construction and operation of Flaming Gorge Dam and Reservoir has <br />significantly altered historic flow and temperature regimes in the Green <br />River and this alteration has been implicated in the decline of Colorado <br />3 <br />