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it is possible that Colorado squawfish movement was in response to a relationships among water temperature and other factors. Further work is needed to better assess these relationships. Red shiner and fathead minnow were also abundant in backwaters. However, their standing crops did not fluctuate with water temperature as did that of young Colorado squawfish. In their native range, these species can spend their entire life cycle in sluggish stream environs (e.g., see Pfleiger 1975), whereas Colorado squawfish do not (Tyus 1986, 1991). As recent invaders from more mesic environs, the former species may tolerate a wider range of environmental conditions than young Colorado squawfish, whereas the squawfish may compensate for a more narrow range of tolerances by incorporating movements into its life history. Because it is generally accepted that backwaters are preferred habitats of young Colorado squawfish in summer and autumn, stream managers may be inclined to provide flows to maximize the amount of backwater habitats rather than to provide a diversity of habitats. The results of my study demonstrated that young Colorado squawfish also use other habitats and may use a mixture of habitats in preference to backwaters. The Upper Colorado River Basin Recovery Implementation Program (U.S. Fish and Wildlife Service 1987) established an interagency monitoring program to sample standing crops of young Colorado squawfish in backwaters, determine their annual abundance, and assess their population trends. The program relies on backwater seine samples for determining the relative abundance of age-O Colorado squawfish. Because the abundance of age-O fish in backwaters can vary with time of day and water temperatures, backwater seining should be further refined to include water temperature criteria. Backwater habitats are extensively used by young squawfish, but the use of other habitats should also be evaluated. ACKNOWLEDGEMENTS This study was funded, in part, by the Bureau of Reclamation and Fish and Wildlife Service, U.S. Department of the Interior. J. Krakker, Jr, J. Kreitlow, B. Burdick, C. Mcada, M. Smith, W. Polinski, and others assisted with field sampling. G. Haines performed statistical analyses. C. Karp and four anonymous reviewers improved the draft manuscript. LITERATURE CITED Berry, C.R. Jr., and R. Pimentel. 1985. Swimming performances of three rare Colorado River fishes. Transactions of the American Fisheries Society 114:397-402. Brown, A.V., and M.L. Armstrong. 1985. Propensity to drift downstream among various species of fish. Journal of Freshwater Ecology 3:3- 17. Harvey, B.C. 1987. Larval stream fish mortality and multi-trophic level interactions among stream fishes. Ph.D. Thesis, University of Oklahoma, Norman. 85 pp. Haynes, C.M., T.A. Lytle, E.J. Wick, and R.T. Muth. 1984. Larval Colorado squawfish (Ptvchocheilus lucius Girard) in the upper Colorado River basin, Colorado, 1979-1981. Southwestern Naturalist 29:21-33. Holden, P.B. 1977. Habitat requirements of juvenile Colorado River squawfish. U.S. Fish and Wildlife Service Report FWS/OBS 77/65. Fort Collins, Colorado 50