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<br />,< <br /> <br />but their distribution is restricted by dams and diversions (Figure 1). The decline of these fishes is <br />attributed primarily to habitat loss and other environmental changes associated with construction of <br />reservoirs and reduced and regulated flows in the remaining potamon reaches of the fragmented <br />river system (Stanford and Ward I986a). Predation by numerous introduced species (Minckley et <br />, . <br /> <br />al. 1991, Tyus I99Ia and b) and toxic effects of selenium from irrigation return flows (Stephens et. <br />al. 1992) also have produced documented pressures on the swvival of these fishes. <br />The recovery program emphasizes reregulation of flows and obtaining water rights to insure <br />long-term stability of flows so that documented environmental needs of the fish can be met over the <br />long term (U.S. Fish & Wildlife Service I987a, 1993). Flow regimes have been formally <br />recommended for the Green River (U.S. Fish & Wildlife Service 1992), Yampa River (U.S. Fish & <br />Wildlife Service 1990) and the I5-mile reach of the main stem Colorado River in the Grand Valley <br />near Grand Junction, Colorado (Kaeding and Osmundson 1989, Osmundson and Kaeding 1991). <br /> <br />However, provision of instream flows is contentious, owing to the high value of water development <br /> <br />entitlements apportioned to Colorado, Utah and Wyoming per the Colorado River Compact. <br /> <br />Indeed, the recovery program is predicated upon development of these entitlements. Contention <br />also has arisen with regard to the efficacy of technical or scientific methods used to justify flow <br /> <br />recommendations. <br /> <br />Puq>ose and Objectives of the Study <br />Owing to contention over flow recommendations developed by the U.S. Fish and Wildlife <br />Service, I was commissioned by the Instream Flow Subcommittee of the Recovery Implementation <br />Program for Endangered Fish Species of the Upper Colorado River Basin to review and synthesize <br /> <br />the science pertinent to the issue. <br /> <br />The objectives of the study were: <br /> <br />(a) to complete a comprehensive review of past and ongoing technical activities, methods <br />and knowledge related to the quantification of instream flows needed for recovery of <br />the four endangered fish species in the Colorado and Green River subbasins, including <br /> <br />3 <br />