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" Olllt.1Si . . Humpback Chub (Gila cypha) , , The Humpback chub was listed as an endangered species in 1973 by ~e U.S. Fish and Wildlife Service. Humpback chub are generally found inhabiting deep waterl in narrow canyon areas, are relatively limited in distribution, and seldom leave their canyon h~itat. They have occasionally been captured in the lower Yampa River in Juniper and Cross ountain canyons. Humpback chub have also been captured in Desolation and Gray Canyons of the Green River. During the spring and summer, Humpback chub are most prevalent in !high gradient, whitewater reaches dominated by rocky runs, riffles and rapids (U.S. Fish aqd Wildlife Service, 1992). Adult fish are most often captured in seasonany flooded shoreline eddies that are downstream of large boulders and upstream of rapids. Fall and winter ~llbitat requirements of Humpback chub are less well understood, however research Indicates that the fish remain in pools and eddies during these periods of lower flows (Karp an~ Tyus, 1989). I Populations of humpback chub exist in Desolation and Gray Canyons f the Green River and in the Yampa and Whirlpool Canyons in Dinosaur National Monument ( addux et. al. 1993b). A single specimen has also been collected in the Yampa River at Cr ss Mountain Canyon (Wick et. al. 1981). Proposed critical habitat in the Yampa and Gre n Rivers includes the Yampa River from Dinosaur National Monument to the confluence with e Green River and the Green River from the confluence with the Yampa River to the southe n boundary of Dinosaur National Monument (Maddux et. al. 1993b). No humpback chub have been observed in the Elkhead Reservoir area or in Elkhead Creek below the reservoir. i i Razorback Sucker (Xyrauchen texanus) i . I The Razorback sucker was listed as endangered in 1991 by the U.S. F\sh and Wildlife Service. There have been very few recorded captures of Razorback suckers \11 recent years. This is believed to be a result of either reproductive failure, predation on eggs and young of the year fish by other species, and competition with exotic. fish species for fopd and habitat. The largest population is presently believed to exist in the Green River and i1 Lake Mohave. During the winter months, Razorback suckers use slow runs, slackwattrs, eddies and backwaters in the Green River, Who ere local movements increased with flow uctuations (Valdez and Masslich, 1989). Breeding Razorback suckers have been found n cobble/gravel/sand bars in the lower Yampa and Green rivers (Tyus and Kal'Jil, 1990). Spawning has been observed during ascending and highest spring peak flows l(Tyus and Karp, 1989). Razorback suckers exhibit both local and long-distance spring and sUlnmer movements (Tyus, 1987). Spawning migrations have been detected between the lower Yjunpa River and the Upper Green River. I i The largest existing riverine population of razorback sucker, an estimafed 1,000 fish, occurs in the Green River from the mouth of the Duchesne River upstream to the Yampa River (Maddux et. al. 1993a; USFWS 1993). Proposed critical razorback habitat blow Elkhead Reservoir includes the Yampa River below Cross Mountain Canyon, the Gre n River from its confluence with the Yampa River to the Colorado River, and the Colorado Rver down to Lake Powell. No razorback sucker have been observed in the Elkhead Reservoir a ea or in Elkhead Creek below the reservoir. i I Bony tail Chub (Gila elegans) i The Bony tail chub was listed as endangered in 1980 by the U.S. Fish Jnd Wildlife Service. Historically, Bony tail chub occurred throughout the Colorado Rive~ mainstem and its I I 10 I , ;1{" -~