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'a Gorge remains impaired, owing to persistent fme sediments within and upon the substratum of the river bottom which prevents establishment of a productive biofilm and restricts attachment sites for zoobenthos. This Gunnison River case history is a classic response to stream regulation. Similar results have been recorded elsewhere (e.g., Petts 1986, Stanford and Hauer 1992). Indeed, an upstream discontinuity clearly exists on the Colorado River (Voelz and Ward 1991) and the Green River (Pearson and Franklin 1968, Pearson et al. 1968), although the latter is significantly reset toward predam potamon conditions by the Yampa River (Annear and Neuhold 1983). Conclusions Based Upon Review of the Ecolo~cal Literature Pertainin~ to the Endan~ered Fishes and the Re~ulation of Flow 1) The endangered fishes remain relatively rare in the Upper Colorado River Basin as a consequence of stream regulation and possibly predation and other interactions with nonnative fishes. Recruitment of adults has not been clearly demonstrated for any of the species, but age structure of squawfish suggests adult recruitment is occuning (Le., larvae, YOY, juveniles and adults are collected each year in the Upper Colorado River Basin, although all age classes often are not obselVed in the same river segments). Clear evidence for adult recruitment is lacking for the other species. In recent years gravid razorback sucker and humpback chub were collected during spawning season at a few sites and a few YOY were collected. Bony tail chub appear to be extirpated. 2) The distribution, relative abundance and some important physical habitat preferences of squawfish, humpback chub and razorback sucker (in that order) are reasonably well known (Figure 6) and documented in peer-reviewed literature. However, only the squawfish life history is fairly well understood. Important aspects of the life history and habitat preferences for humpback chub and razorback sucker remain to be documented. Indeed, much of what is known about the life history and population dynamics of humpback chub is based on unpublished studies in the Grand Canyon, which mayor may not be relevant to the Upper Basin (e.g., no population in the Upper 41