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1 <br /> <br /> <br />1 <br /> <br />1 <br />1 <br /> <br /> <br />t <br /> <br /> <br />1 <br /> <br /> <br />INTRODUCTION <br />The native fish fauna of the Colorado River basin is an unique natural <br />resource that has existed for millennia. Colorado squawfish (Ptychocheilus <br />lucius), humpback chub (Gila cypha}, bonytail chub (G. elegans), and razorback <br />sucker (Xyrauchen texanus) are four endemic fishes that were historically <br />common-to-abundant in rivers of the Colorado River basin. All four species <br />were collected in the lower Yampa and upper Green rivers (Dinosaur National <br />Monument (DNM)) prior to closure of Flaming Gorge Dam in 1962 (Vanicek and <br />Kramer 1969). However, these fishes are threatened with extinction throughout <br />the Colorado River basin due to combined effects of habitat loss and <br />alteration, introduction of non-native competitors and predators, and other <br />man-induced impacts. The Colorado squawfish, humpback chub, and bonytail chub <br />are federally listed as endangered species; razorback sucker is protected by <br />the states of Arizona, California, Nevada, Colorado, and Utah, and is a <br />candidate species for federal listing (USFWS 1987a). The decline of these big <br />river fishes is a biological indicator of change and impending loss of an <br />unique and historic ecosystem. <br />Flow regimens have been substantially altered by dams. in all large rivers <br />in the upper Colorado River basin except the Yampa River (Figure 1). As <br />indicated in Figure 2, flows of the Yampa River are not significantly <br />different from historic conditions, and spring runoff from this system <br />maintains the spring/early summer peak in the existing Green River hydrograph <br />(downstream from the Yampa River confluence). Alteration of the natural flow <br />regimen of the Yampa River due to construction of water projects (e. g. <br />Stagecoach and Juniper-Cross Mountain projects on the Yampa River, Cheyenne <br />1 <br />