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229 <br />changes in species composition. Construction dis- <br />turbance of the river channel, habitat conditions of <br />the reservoir, and changes in conditions below the <br />dam all appeared to favor proliferation of certain <br />non-native species. The final provision of the bio- <br />logical opinion issued for the Taylor Draw Reser- <br />voir Project (U.S. Department of the Interior, Fish <br />and Wildlife Service, 20 May 1982) required devel- <br />opment of a fishery in Kenney Reservoir that would <br />not compete with endangered species in the White <br />River. While agency stocking programs empha- <br />sized a salmonid fishery to accommodate this provi- <br />sion, local enthusiasm for warmwater sport fishes <br />resulted in illicit introductions of warmwater sport <br />fishes from nearby impoundments in both Colora- <br />do and Utah. In this paper we document these <br />changes in the ichthyofauna in the White River, <br />Colorado, following the construction of Taylor <br />Draw Dam and formation of Kenney Reservoir. <br />Study area <br />The White River was one of the few remaining free- <br />flowing tributaries in the entire Colorado River Ba- <br />sin (Stanford & Ward 1986a). A major tributary in <br />the Green River subbasin (Fig. 1), the White River <br />drains more than 13 000 km' in Colorado and Utah. <br />The White River flows about 400 km from its <br />source in Colorado's Flattop Mountains to its con- <br />fluence with the Green River at Ouray. Utah. Loca- <br />tions along the river were demarcated as river ki- <br />lometers (RK) upstream from its confluence with <br />the Green River. <br />Taylor Draw Dam was completed on the White <br />River in October 1984, about 16 km east of Rangely, <br />Colorado, at RK 167.8. Kenney Reservoir, which <br />filled by January 1985, inundated about 10 km of the <br />river (to RK 176.9; Fig. 1). The reservoir was origi- <br />nally 275 ha. had a maximum depth of 15.2 m. and a <br />volume of 17 million cubic meters of water at a max- <br />imum elevation of 1620 meters above sea level; <br />however, these capacities have decreased an unde- <br />termined amount due to sediment deposition, par- <br />ticularly in the upper portion of the reservoir <br />(Trammell 1991). Kenney Reservoir is about 8 km <br />long and 1.2 km at its widest point. Aside from im- <br />poundment, the dam's influence on hydrologic and <br />thermal conditions in the White River were subtle <br />(Chart & Bergersen 1992). <br />Fish collections were made from RK 115.5, the <br />Colorado/Utah stateline, to RK 184.6, about 9 km <br />above the reservoir basin. The White River in this <br />area ranged in width from 20 to 50 m. Channel sub- <br />strates were primarily cobble and rubble in flowing <br />areas and silt and sand in slower moving sections. <br />The hydrologic regime is characterized by extremes <br />in flow, with highest discharge during snowmelt in <br />spring and early summer, and lowest in late summer <br />and early fall. Turbidities of the river are typically <br />high in spring and during summer rainstorms. Sum- <br />mer water temperatures exceed 20° C, and the envi- <br />ronment has been described as coolwater/warmwa- <br />ter (Martinez', McConnell et al.'). This segment of <br />the White River meanders through an agricultural <br />valley bordered by low rocky hills. Near the Col- <br />orado/Utah state line, surrounding lands become <br />more barren as the river flows through canyon ar- <br />eas. This topography supports vegetation charac- <br />teristic of this semi-arid region (Wullschleger 1990). <br />Investigations of the river's fish community in <br />Colorado in the years preceding construction of the <br />dam showed that native species dominated (Carl- <br />son et al.' and Tyus et al. 1982). Fish collections re- <br />ported in Carlson et al.' during 1975-1977 revealed <br />that seven native species comprised 94.0% of fishes <br />collected while five non-native species accounted <br />for 6.0%. Miller et al! recorded five native species <br />accounting for 75.8% of the ichthyofauna and six <br />non-native species comprising 24.2% in two <br />reaches included in our study area. Lanigan & Ber- <br />ry (1981) showed non-native species dominated fish <br />collections in Utah in 1978-1979, but native fishes <br />' McConnell. W.J., E.P. Bergersen & K.L. Williamson. 1984. <br />Habitat suitability index models: a low effort system for planned <br />coolwater and coldwater reservoirs (revised). U.S. Fish and <br />Wildlife Service FWS/OBS-82/10.3A, Fort Collins. 62 pp. <br />' Carlson, C.A., C.G. Prewitt. D.E. Snyder. E.J. Wick, E.L. <br />Ames & W.D. Fronk. 1979. Fishes and macroinvertebrates of the <br />White and Yampa River. Colorado. Biological Sciences Series 1. <br />Bureau of Land Management. Denver. 276 pp. <br />Miller. W.H., D.L. Archer. H.M. Tyus & K.C. Harper. 1982. <br />White River fishes study. Colorado River Fishery Project. U.S. <br />Fish and Wildlife Service. Salt Lake City. 23 pp.