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26 Habitat requirements of young and juvenile razorback suckers in the wild are largely unknown, particularly in native riverine environments. Prior to 1991, the last confirmed documentation of razorback sucker juveniles in the Upper Basin was a capture in the Colorado River near Moab, Utah (Taba et al. 1965). In 1991, two early juvenile (36.6 and 39.3 mm TL) razorback suckers were collected in the lower Green River near Hell Roaring Canyon (Gutermuth et al. 1994). Razorback sucker larvae also have been collected from Jensen, Utah, above the Jensen Bridge to the Ouray Bridge on the Green River from 1992 to present (Robert Muth, pers.comm.). Additionally, limited numbers of razorback young-of-year were captured in Old Charlie Wash in 1995 (Modde 1996) and 1996 (Tim Modde, pers.comm.). Also, a few larval razorback suckers have been collected below the confluence of the Yampa and Green rivers. The RIP currently is engaged in an intensive effort to restore and manage flooded bottomland habitats for the overall benefit of endangered fishes. Naturally functioning, highly productive low-velocity habitats which provide food, enhanced water temperatures, shelter from high velocities, nursery rearing habitats and spawning habitats are thought to be an essential component of the life history of some or perhaps all of the native and endangered fishes, including the razorback sucker. Throughout the Upper Colorado River Basin, however, many such habitats have been hydrologically cut off from the main channel of the rivers and are no longer accessible to native and endangered fishes. The Service believes that successful restoration of functional floodplain habitats of~sufficient quantity, quality and spatial distribution to support survival, growth, reproduction, and recruitment will contribute to recovery of razorback sucker. The humpback chub is endemic to the Colorado River Basin and is part of a native fish fauna traced to the Miocene epoch in fossil records (Miller 1955, Minckley et al. 1986). Humpback chub remains have been dated to about 4000 B.C., but the fish was not described as a species until the 1940's (Miller 1946), presumably because of its restricted distribution in remote white water canyons (USFWS 1990b). Because of this, its original distribution is not known. Until the 1950's, the humpback chub was known only from the Grand Canyon. During surveys in the 1950's and 1960's humpback chub were found in the upper Green River including specimens from Echo Park, Island Park, and Swallow Canyon (Smith 1960. Vanicek et a1.,1970). Individuals also were reported from the lower Yampa River (Holden and Stalnaker 1975b), the White River in Utah