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Razorback sucker Razorback suckers were historically common in the portions of the UCRB, including the ~ mainstream Green and UCR (reviewed by Minckley et al. 1991). In the UCR, fish have been reported from Moab, UT to Rifle, CO (Kidd 1977, Burdick 1992, Westwater Engineering 1996). Juvenile razorbacks were captured near Moab in the 1960's (Taba et al. 1965). More recent collections (Valdez et al. 1982, Archer et al. 1985, Osmundson and Kaeding 1989) have shown very low and declining numbers below ~ Palisade. Above Palisade, a few individuals have been reported from Highline Lake and isolated ponds near Rifle and Debeque (Burdick 1992). The largest remaining population of razorback suckers occurs in Lake Mohave of the lower basin of the Colorado River. Because recruitment is very low, the population continues to decline in abundance (Marsh 1995). The only remaining riverine ~ population occurs in the Green River near the confluence with the Yampa River; it consists of less than 1,000 fish and may be declining (Lanigan and Tyus 1989, Modde et al. 1996). A few individuals also have been collected in the mainstream Colorado River and in the lower San Juan River. In the upper Colorado River, 47 razorback suckers were collected during the two years of the baseline survey, but most of these ~ (79%) came from two flooded gravel pits: Walter Walker State Wildlife Area (RM 164) and Clifton Pond (RM 118; Valdez et al. 1982). Captures of razorback suckers declined in the UCR from 1974 to 1988 (Osmundson and Kaeding 1991), and only one individual was captured in six years of the ISMP (McAda et al. 1994). The species has probably been extirpated from the UCR. Furthermore, there is no indication that recruitment is ~ adequate to support existing populations (McAda and Wydoski 1980; Meyer and Moretti 1988; Lanigan and Tyus 1989; Modde et al. 1995). Bonytail ~ The bonytail was apparently common in some portions of the UCRB, including the Green River (USFWS 1990a), but it may never have been common in the UCR (Westwater Engineering 1996). It is thought to have been extirpated from the UCRB (Valdez and Clemmer 1982). The last individuals reported in the basin were one fish captured near Black Rocks (Kaeding et al. 1986) and five captured in Cataract Canyon (Valdez and Williams 1993). The few individuals that have been captured in Lake Mohave may represent the last of the species in nature. All other individuals exist as hatchery stocks. Virtually nothing is known about the life history of this species except that it inhabited the main channel of large rivers and also could survive in reservoirs (USFWS 1990a). • 7 C~