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<br /> <br /> <br />1 <br /> <br /> <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br />1 <br /> <br /> <br /> <br /> <br />In the lower basin, razorback sucker apparently began to decline shortly after <br />impoundment of Lake Mead in 1935 (Dill 1944, Miller 1946, Wallis 1951, Jonez and <br />Sumner 1954, Allen and Rodman 1978). Larval and juvenile razorback suckers have <br />been reported widely from the lower basin, and larvae are regularly captured in Lake <br />Mojave (reviewed by Minckley et al. 1991). The largest extant population occurs in <br />Lake Mohave, where the population consisted of approximately 60,000 adults in 1986 <br />(Minckley et al. 1991). By 1995, that population had declined to about 25,000 fish <br />(Marsh 1995). Small numbers of razorback suckers occur in Lake Mead and in the <br />Grand Canyon, where individuals are found sporadically downstream on the mainstem <br />river, and assocated impoundments and canals (Marsh and Minckley 1989). <br />In the upper basin, the present range of the razorback sucker is much less than its <br />historical distribution (Holden and Stalnaker 1975, McAda and Wydoski 1980, Tyus et <br />al. 1982). Adults and larvae are widely distributed in the Green River basin; the largest <br />concentration is in the upper Green River, in a reach that extends from the mouth of the <br />Duchesne River upstream to the lower 4 miles of the Yampa River. Lanigan and Tyus <br />(1989) estimated that about 1,000 adult razorback suckers (x=948, 95% confidence <br />interval: 758-1,138) inhabited the upper Green River basin. Amore recent analysis <br />suggests that this population is "precariously low," consisting of only about 500 fish <br />(z=524, 95% confidence interval: 351-696)(Modde et al. 1996). A small, reproducing <br />population of razorback suckers exists in the lower Green River; 18 adult fish and <br />9 <br /> <br />