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FWS/GJ-6-CO-92-F-007 • Bonvtail chub Page 4 Little is known about the biological requirements of the bonytail chub, as the species greatly declined in numbers in the upper basin shortly after 1960. Until recently, the Service considered the species extirpated from the upper basin; however, a recently collected specimen which exhibits many bonytail characteristics could indicate a small, extant population. It is thought that, should this species persist in the Colorado River, the preferred habitat would be larger river reaches in the Colorado River. Conservation Measures outlined below will contribute to conservation efforts for the bonytail chub, thus offsetting the likelihood of jeopardy for the species. Razorback sucker The current distribution and abundance of razorback suckers have been significantly reduced throughout the Colorado River system (Holden and Stalnaker 1975, McAda and Wydoski 1980, Minckley 1983, McAda 1987, Tyus 1987, Marsh and Minckley 1989). Above Glen Canyon Dam, razorback suckers are found in limited numbers in both lentic and lotic environments. The largest population of razorback suckers in the upper Colorado River basin is found in the upper Green River and lower Yampa River (Tyus 1987). Lanigan and Tyus (1989) estimated that from 758 to 1,138 razorback suckers inhabit the upper • Green River. In the Colorado River, most razorback suckers occur in the Grand Valley area near Grand Junction, Colorado; however, they are increasingly rare. Osmundson and Kaeding (1990) report that the number of razorback sucker captures in the Grand Junction area have declined dramatically since 1974. Specific information on biological and physical habitat requirements of the razorback sucker is very limited. Habitat requirements of young and juvenile razorback suckers in the wild are largely unknown, particularly in native riverine environments. Life stages, other than adults, have not been collected anywhere in the upper Colorado River basin in recent times. The last confirmed documentation of a razorback sucker juvenile in the upper Colorado River basin was a capture in the 1960's in the Colorado River near Moab, Utah (Taba et al. 1965, report in Bestgen 1990). The virtual absence of any recruitment suggests a combination of biological, physical, and/or chemical factors that may be effecting the survival and recruitment of early life stages of razorback suckers. Conservation Measures outlined below will contribute to conservation efforts for the razorback sucker, thus offsetting the likelihood of jeopardy far the species. CONSERVATION MEASURES On January 21-22, 1988, the Secretary of the Interior, the governors of Wyoming, Colorado, and Utah, and the Administrator of the Western Area Power Administration were cosigners of a Cooperative Agreement to implement the "Recovery Implementation Program for Endangered Fish Species in the Upper Colorado River Basin" (Recovery Program). An objective of the Recovery Program was to identify reasonable and prudent alternatives that would ensure i the survival and recovery of the listed species while providing for new water development in the Upper Colorado River Basin.