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<br />The Yampa River is the only large river in the <br />Colorado River basin in which flow patterns have not <br />been substantially altered by water development <br />projects (Fig. 2). Examples of downstream alterations <br />include modification of flow and temperature patterns, <br />and channel morphology. Upstream loss of ftsh habitat <br />can occur with stream blockage and impoundment. <br />Construction of the Flaming Gorge and Fontenelle <br />dams on the Green River in the 1960's eliminated spring <br />peak flows and increased baseline discharge in that <br />system. However, the spring and early summer peak in <br />the existing Green River hydrograph below the <br />confluence of the Yampa River is maintained by spring <br />runoff from the Yampa River (Fig. 3). <br />Fishes indigenous to the Yampa River include <br />cyprinids (Colorado squawfish [Ptychocheilus IIlCillS], <br />humpback chub [Gila cypha], bonytail chub [G. elegans], <br />roundtail chub [Gila robustaj, speckled dace <br />[Rhinichthys osclllus]); catostomids (razorback sucker <br />[Xyrallchen t"""nus], flannelmouth sucker [Catostomlls <br />latipinnis], bluehead sucker [e. discobolus], mountain <br />sucker [e. platyrhynchlls]): salmonids (Colorado River <br />cutthroat trout [Salmo clarki plellriticllS]; Rocky <br />Mountain whiteftsh [Prosopium williamsoni]): and <br />sculpins (Cottus bairdi sp.; Tyus et a!. 1982a; Behnke and <br />Benson 1983; Woodling 1985). All mainstream ftshes <br />persist today despite the introduction of at least 18 <br />nonnative ftshes (Tyus et a!. 1982a; Wick et a!. 1985; U.S. <br />Fish and Wildlife Service, unpublished data). Native <br />ftshes also dominate the Yampa River ftsh community <br />as indicated by Miller et a!. (1982) and Wick et a!. (1985). <br />Using electroftshing and trammel netting techniques, <br />these investigators found that native fiShes composed <br />more than 70% of the catch, and Miller et al. (1982) <br />reported that 54% of all ftshes captured (including <br />collections of small ftshes) were native. Persistence of <br />native ftshes is most often observed in unaltered <br />(natural) river systems (e.g., Yampa River and Little <br />Colorado River) and is presumably associated with <br />maintenance of usable ftsh habitat due to a regimen of <br />fluctuating seasonal and annual flows. <br />Historically, the native cyprinids and catostomids <br />were the dominant fiShes in mainstream habitats of the <br />Colorado River basin. The Colorado squawfish, <br />bonytail chub, humpback chub, and razorback sucker <br />were widely distributed and common-to-abundant in <br />major rivers of the Colorado River basin. However, all <br />four species are now threatened with extinction due to <br />the combined effects of habitat loss; regulation of <br />natural flow, temperature, and sediment regimes; <br />proliferation of introduced competitors and predators; <br />and other man-induced disturbances (Miller 1%1; <br />Minckley 1973; U.S. Fish and Wildlife Service 1987). <br />The Colorado squawfish, humpback chub, and bonytail <br />chub are federally protected as endangered species <br /> <br />under provisions of the Endangered Species Act of 1973 <br />(U.S. Fish and Wildlife Service 1986). The razorback <br />sucker, a candidate species for Federal listing, is <br />protected by State statutes in Arizona, California, <br />Colorado, Nevada, and Utah (U.S. Fish and Wildlife <br />Service 1985, 1987). <br />In the lower Colorado River basin (below Lee Ferry, <br />Arizona), the Colorado squawfiSh has been extirpated; <br />relict populations ofbonytail chub and razorback sucker <br />remain in some impoundments; and the humpback chub <br />persists only in the Little Colorado River (Minckley <br />1973, 1983). In the upper Colorado River basin, the <br /> <br />'00 <br /> <br />-~ <br />.~_.._-.____ QAEEHOAl..E <br />-YNiII'A <br /> <br />'" <br /> <br />'" <br />g <br />~ 280 <br />~ <br />U <br />~ <br /> <br /> <br />'" <br /> <br />-,,"- '--'."" <br /> <br />OCT MlV DEe .....,. FEI tM.ll NOR IdAY AJN M A~ "' <br /> <br />'00 <br /> <br />-~.. <br />------.-,-, QI&N)ALE <br />-YAW#A <br /> <br />,,' <br /> <br />~ <br />~280 <br />< <br />, <br />~ <br />o <br /> <br /> <br />140 <br /> <br />o ._-____""v"!v--V"'\; "'\_'.r-~"""""\..'_;'/. <br /> <br />-n'......._- <br /> <br />OCT NOli oec J.IoI'l f'E8 MAR APli: Mol-Y JUN JU. ",UQ SEP <br /> <br />MONTI-! <br /> <br />Fig. 3. Averageannualdistribution hydrographfor the Green <br />and Yampa rivers. Upper figure for 1951~2; lower figure <br />for 1964-84. USGS flow records: Jensen = Green River at <br />Jensen, Utah; Greendale = Green River below Flaming <br />Gorge Dam; Yampa = Yampa River at mouth (Yampa <br />River near Maybell, Colorado, and Little Snake River near <br />Lily, Colorado). <br /> <br />3 <br />