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Idtthyofauna of the Colorado and Green Rivers in Canyonlands National Park, Utah I. assess the distribution and relative abundance of all fish species, 2. determine spawning locations and nursery areas of endangered fishes, and 3. confirm the existence of a population of humpback chub in Cataract Canyon. :s- ~ 00 Richard A. Valdez BIO/WEST, fllc. 1063 West 1400 North Logal/, Utah 84321 The Colorado and Green rivers in and adjacent to CNP are among the last reaches of the upper Colorado River to be intensively surveyed for fishery resources. Valdez et al. (1982) first sampled the area from 1979 through 1981 and reported numerous young Colorado squawfish, small num- bers of humpback chub, and large numbers of nonnatives. The area received much allention in April 1980 when 45 adult Colorado squaw fish were cap- tured in the Lake Powell inflow as part of an investigation of striped bass (Morol/e saxililis; Persons et al. 1982). As a result of these findings, the Bureau of Reclamation radio-tagged adult Colorado squaw fish in the inflow from 1982 to 1985 in an allempt to locate fish concentrations, monitor movements, and identify possible spawning areas. The investigation we describe began as a pilot study in Cataract Canyon in 1985 to identify Colorado squawfish spawning sites and to confirm a reproducing populati9n of humpback chub. From 1986 through 1988, the investigation was expanded to characterize the ichthyofauna of the lower 80 km of the Colorado and Green rivers above their confluence; the Colorado River through Cataract Canyon; and the Lake Powell inflow (Valdez 1990). Robert D. Williams U.s. Fish al/d Wildlife Sen'ice Sail Lake City, Utah 84147 Abstract. Thirty-one species of fish were found in the Colorado and Green rivers in and adjacent to Canyonlands National Park during 1985-88 in the first intensive ichthyofaunal survey of the area. We found 8 native species (5% of total number) and 23 nonnative species (95%). The four species of endemic mainstcm fishes that are federally classified as endangered were present-Colorado squawfish (PI)'c/lOclleilus lucius), humpback chub (Gila c)'plla), bonylail (G. elegans), and razorback sucker (Xyraucllen lexallus). Numerous age-O (young-of-year) Colorado squawfish were found as were small numbers of juveniles and adults. A reproducing population of humpback chub was confirmed in Cataract Canyon, and six suspected bony tail were found. Only one adult razorback sucker was caplUred. Endemic roundtail chub (G. robusla) and flannel mouth sucker (Catostomlls lat;p;lIn;s), as well as nalive bluehead sucker (c. discobollls) and speckled dace (Rhillichtllys osclIIIIS), were also present in low numbers. The most common species in backwaters and shorelines were nonnative red shiners (C)'pr;ne/la IIIIrens;s), sand shiners (Notropis slram;lIells), and fathead minnows (Pimeplwles promelas), while channel catfish (lelalllms '" pllncla/us) and common carp (C)'prill/ls carpio) were Ihe dominant main channel E species. . .- - - 9 +' Study Area This investigation was conducted on the Colorado River in Utah from Potash (river kilometer (RK) 80) downstream to Imperial Canyon in upper Lake Powell (RK 316, 34 km below the confluence of the Colorado and Green rivers), as well as that portion of the Green River from Mineral Bottom (RK 80) downstream to the confluence (Fig. I). This area represents the lowermost free-flowing reach of the upper Colorado River basin (i.e., above Lees Ferry). Detailed maps of the Colorado and Green rivers in this area are available in two river guides (Belknap and Belknap 1974; Baars 1987). Distances above the confluence are measured in river kilometers from that point while distances below the confluence are measured from Lees Ferry (i.e., the confluence is 350 km upstream of Lees Ferry). The Colorado and Green rivers in the study area flow through lands administered by the National Park Service (CNP and Glen Canyon National Recreation Area (GCNRA]) and the Bureau of Land Management, and they enter CNP 55 and 76 km upstream from their confluence, respectively. The river leaves CNP and enters GCNRA at RK 328,22 km below the confluence. The Colorado River flowed into Lake Powell during this investigation be- tween RK 325 (1,123 m elevation) and RK 326 (at a maximum lake elevation Key words: Bony tail, Canyonlands National Park, Cataract Canyon, Colorado River endangered fish, Colorado River ichthyofauna, Colorado squawfish. humpback chub, razorback sucker. Our purpose was to characterize the ichthyofauna of the Colorado and ., Green rivers in and adjacent to Canyonlands National Park (CNP) and to ~ assess the importance of the area to the endangered Colorado River fishes: -G Colorado squawfish (PtycllOcheillls IllcillS), humpback chub (Gila cypha), .... bony tail (G. elegal/s), and razorback sucker (Xyrallchell texOfllls). The objec- .. tives of the investigation were to :> tt' 0'-2 =r- -