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and Miller 1963, Baxter and Simon 1970, Vanicek et al. 1970). Razorback suckers also have been captured in the lower few miles of the Duchesne River (Tyus 1987) and in the lower White River near Ouray, Utah (Sigler and Miller 1963). Razorback suckers occurred in the lower Yampa and Little Snake rivers of Colorado (McAda and Wydoski 1980, Lanigan and Tyus 1989, John Hawkins, Colorado State University, pers. comm., 1995). Historic status of the razorback sucker in the San Juan drainage is not well documented (Bestgen 1990), but there is ample evidence that the fish historically occurred there. Early accounts that razorback suckers "ran" up the tributary Animas River in spring (Jordan 1891) presumably represent spawning migrations. Koster (1960) reported anecdotal evidence of razorback suckers captured by anglers in the Animas River, and in 1992, anglers identified razorback sucker pictures as the fish they had captured in the Animas River during the 1940s. Anecdotal accounts indicate that razorback suckers were observed in irrigation ponds and perhaps in the mainstream river near Bluff, Utah, in 1977 (Minckley et al. 1991). The first verified record of razorback suckers from the San Juan River consisted of a 571 mm adult in spawning condition captured in 1988 from the mainstream river near Bluff (Platania et al. 1991). Present In the lower basin, razorback sucker apparently began to decline shortly after impoundment of Lake Mead in 1935 (Dill 1944, Miller 1946, Wallis 1951, Jonez and Sumner 1954, Allen and Roden 1978). Larval and juvenile razorback suckers have been reported widely from the lower basin, and larvae are regularly captured in Lake Mojave (reviewed by Minckley et al. 1991). The largest extant population occurs in Lake Mojave, where the population consisted of approximately 60,000 adults in 1988 (Minckley et al. 1991). By 1995, that population had declined to about 25,000 fish (Marsh 1995). Small numbers of razorback suckers occur in Lake Mead and in the Grand Canyon, where individuals are found sporadically downstream on the mainstream river, and associated impoundments and canals (Marsh and Minckley 1989). In the upper basin, the present range of the razorback sucker is much less than its historical distribution (Holden and Stalnaker 1975, McAda and Wydoski 1980, Tyus et al. 1982). Adults and larvae are widely distributed in the Green River basin; the largest concentration is in the upper Green River, in a reach that extends from the mouth of the Duchesne River upstream to the lower 4 miles of the Yampa River. Lanigan and Tyus (1989) estimated that about 1,000 adult razorback suckers (x=948, 95% confidence interval: 758-1,138) inhabited the upper Green River basin. Amore recent analysis suggests that this population is "precariously low," consisting of only about 500 fish (x=524, 95% confidence interval: 351-696)(Modde et al. 1996). A small, reproducing population of razorback suckers exists in the lower Green River; 18 adult fish and numerous larvae have been captured there from 1980-1996 (Tyus et al. 1987; McAda et al. 1994; 1996; Muth et al. 1998). Although the fish regularly occurs in the lower Yampa, it is rarely found upstream as far as the Little Snake River (McAda and 6