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SUCKER WETLAND USE losses of floodplain wetland habitat, the potential negative influence of nonnative fishes cannot be dismissed. The numbers and biomasses of fishes in our study area were dominated by nonnatives, particularly lentic-adapted species. Marsh and Langhorst (1988) and Minckley et al. (1991) con- sidered predation to be the major factor limiting recruitment of razorback suckers in Lake Mohave, a main-stem impoundment on the lower Colorado River. The abundance of nonnative fishes in Old Charley Wash likely reduced razorback sucker sur- vival through predation or competition, particu- larly by species that reproduce in wetlands, such as black bullhead and green sunfish. However, de- spite interactions with nonnative fishes, some ra- zorback sucker juveniles survived to the end of the growing season. Because the study wetland was dry prior to spring flood flows, there was no impact of residual nonnative fishes. If residual nonnative fishes have an impact on razorback sucker recruitment in floodplain wetlands, then this study suggests that either draining wetlands before the spring or facilitating larval access to floodplain wetlands following low-flow years (i.e., years in which floodplains dry) would provide the best opportunity for razorback sucker recruitment. However, this study indicated that even in the pres- ence of large numbers of nonnative fishes, larval and juvenile razorback suckers survived in a nat- ural floodplain habitat. Although the greatest number of razorback suckers exist in lower Colorado River impound- ments, they represent senescent populations that recruited as the impoundments initially filled (Minckley et al. 1991). Floodplain habitats in the lower Colorado River are either flooded by res- ervoirs or isolated by levees or channel incision. The middle Green River retains much of its flood- plain habitat (Irving and Burdick 1995) even though inundation is less than under predam con- ditions (Flo Engineering 1996). The recruitment of razorback suckers is linked with high-discharge events (Modde et al. 1996), and this study provides evidence of larval and juvenile use of floodplain wetlands. Recovery of razorback suckers will de- pend on identification of impediments to recruit- ment (Wick et al. 1982). The growth and survival of larvae and juvenile razorback suckers in Old Charley Wash suggest that some natural recruit- ment is possible if suitable floodplain habitat is provided in a timely manner. If historical habitat can be restored for razorback suckers, predation by nonnative fishes may be a secondary rather than 1103 the prevalent force impacting the recovery of this species. Acknowledgments This study was funded by the Recovery Imple- mentation Program for Endangered Fish Species in the Upper Colorado River Basin. The program is a joint effort of the U.S. Fish and Wildlife Ser- vice, the U.S. Bureau of Reclamation, the Western Area Power Administration, the states of Colora- do, Utah, and Wyoming, upper basin water users, environmental organizations, and the Colorado River Energy Distributors Association. Ed Wick and Harold Tyus first suggested the linkage of wet- lands to razorback suckers in the Upper Colorado River basin and provided the impetus to initiate this study. Pat Nelson, Recovery Implementation Program floodplain restoration coordinator, pro- vided guidance and direction throughout the study. Special thanks go to Steve Brock and the staff of the Ouray National Wildlife Refuge for their per- mission to work on the refuge and their assistance in planning and implementing the study. Data on unregulated flow in the Green River were provided by Tom Ryan of the Bureau of Reclamation. Ap- preciation is extended to Peter Bayley, Eugene Maughan, and W. L. Minckley for their time and expertise in reviewing drafts of this manuscript. References Bestgen, K. R. 1990. Status review of the razorback sucker, Xyrouchen texanus. Colorado State Univer- sity, Larval Fish Laboratory Contribution 44, Fort Collins. Boehlert, G. W. 1981. Ontogenetic changes in growth and their relationship with temperature and habitat change. Pages 115-123 in G. Cailliet and C. A. Simenstad, editors. Proceedings of the third Pacific workshop. University of Washington, Washington Sea Grant Publication, Seattle. Boyd, C. E. 1979. Water quality in warmwater ponds, Auburn University Agricultural Experiment Sta- tion, Auburn, Alabama. Bulkley, R. V., and R. Pimental. 1983. Temperature preference and avoidance by adult razorback suck- ers. Transactions of the American Fisheries Society 112:601-607. Carlson, C. A., and R. T. Muth. 1993. Endangered spe- cies management. Chapter 15 in C. C. Kohler and W. A. Hubert, editors. Inland fisheries management. American Fisheries Society, Bethesda, Maryland. Flo Engineering. 1996. Green River flooded bottomland investigations: Ouray Wildlife Refuge, Canyonland National Park, Utah. Draft report submitted to the Recovery Implementation Program for the Endan- gered Fish Species in the Upper Colorado River Basin, U.S. Fish and Wildlife Service, Denver.