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• are relatively restricted in distribution. They seldom leave their canyon <br />habitat (Service 1982). While humpback chub are regularly found dispersed in <br />the Green and Yampa Rivers, the only major populations of humpback chub known <br />to exist in the upper Colorado River basin are located in Black Rocks and <br />Westwater Canyons on the Colorado River. Conservation Measures outlined below <br />will contribute to providing proper habitat conditions for humpback chub, thus <br />offsetting the likelihood of jeopardy for the species. <br />Bonvtail chub <br />Little is known about the biological requirements of the bonytail chub, as the <br />species greatly declined in numbers in the upper basin shortly after 1960. <br />Until recently, the Service considered the species extirpated from the upper <br />basin; however, a recently collected specimen which exhibits many bonytail <br />characteristics could indicate a small, extant population. It is thought <br />that, should this species persist in the Colorado River, the preferred habitat <br />would be larger river reaches in the Colorado River. Conservation Measures <br />outlined below will contribute to conservation efforts for the bonytail chub, <br />thus offsetting the likelihood of jeopardy for the species. <br />Razorback sucker <br />The current distribution and abundance of razorback suckers have been <br />significantly reduced throughout the Colorado River system (Holden and <br />Stalnaker 1975, McAda and Wydoski 1980, Minckley 1983, McAda 1987, Tyus 1987, <br />Marsh and Minckley 1989). Above Glen Canyon Dam, razorback suckers are found <br />• in limited numbers in both lentic and lotic environments. The largest <br />population of razorback suckers in the upper Colorado River basin is found in <br />the upper Green River and lower Yampa River (Tyus 1987). Lanigan and Tyus <br />(1989) estimated that from 758 to 1,138 razorback suckers inhabit the upper <br />Green River. In the Colorado River, most razorback suckers occur in the Grand <br />Valley area near Grand Junction, Colorado; however, they are increasingly <br />rare. Osmundson and Kaeding (1990) report that the number of razorback sucker <br />captures in the Grand Junction area have declined dramatically since 1974. <br />Specific information on biological and physical habitat requirements of the <br />razorback sucker is very limited. Habitat requirements of young and juvenile <br />razorback suckers in the wild are largely unknown, particularly in native <br />riverine environments. Life stages, other than adults, have not been <br />collected anywhere in the upper Colorado River basin in recent times. The <br />last confirmed documentation of a razorback sucker juvenile in the upper <br />Colorado River basin was a capture in the 1960's in the Colorado River near <br />Moab, Utah (Taba et al. 1965, report in Bestgen 1990). The virtual absence of <br />any recruitment suggests a combination of biological, physical, and/or <br />chemical factors that may be effecting the survival and recruitment of early <br />life stages of razorback suckers. Conservation Measures outlined below will <br />contribute to conservation efforts for the razorback sucker, thus offsetting <br />the likelihood of jeopardy for the species. <br />CONSERVATION MEASURES <br />• On January 21-22, 1988, the Secretary of the Interior, the governors of <br />Wyoming, Colorado, and Utah, and the Administrator of the Western Area Power <br />Administration were cosigners of a Cooperative Agreement to implement the <br />