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I CHAPTER III AFFECTED ENVIRONMENT Table III-B-1 Native Fishes of the Upper Colorado River Basin Family/Common Name Scientific Name Status) Abunda Salmonidae Mountain whitefish Prosopium williamsoni N C Colorado River cutthroat trout Salmo clarki pleuriticus E R Cyprinidae Humpback chub Gila cypha E, FE R Bonytail chub Gila elegans E, FE R Roundtail chub Gila robusta E C Colorado squawfish Ptychocheilus lucius E, FE R Speckled dace Rhvnichthvs osculus N A Kendall Warm Springs Rhvnichthvs osculus E, FE R dace thermalis Catostomidae Bluehead sucker Catostomus discobolus N A Flannelmouth sucker Catostomus latipinnis E A Mountain sucker Catostomus platvrhynchus N C Razorback sucker Xyrauchen texanus E R Cottidae Mottled sculpin Cottus bairdi N C 1. N = Native, E = Endemic, FE = Federally listed as endangered 2. R = Rare, A = Abundant, C = Common Young-of-the-year Colorado squawfish are usually captured in shallow backwaters, shoreline habitats with silt and sand substrates and little or no current. High concentrations of juveniles are found in the Green River between Green River, Utah, and the confluence of the Green River with the Colorado River. The highest density of young-of-the-year fish occurs 100- 150 miles below the Green and Yampa River spawning areas. A high-density young-of-the-year area also occurs in the upper Professor Valley of the Colorado River. Humpback Chub Adult humpback chub occupy canyon habitats over a variety of substrates. Their distribution is primarily restricted to the Colorado River at Black Rocks and Westwater Canyon, Gray Canyon of the Green River, and Yampa Canyon of the Yampa River (Figure III-B-2). Confirmed spawning areas occur at Black Rocks and Yampa Canyon. Spawning occurs between April and July, depending on III-1