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Juvenile largemouth bass were collected in the Fall of all years between 1979 and 1993 (Appendix D) by seining backwaters of the Upper Colorado River during sampling by the U.S. Fish and Wildlife Service (1979-1985) or during the Recovery Program's Interagency Standardized Monitoring Program (ISMP) from 1986 through 1993 for Colorado squawfish and humpback chub (McAda et al. 1994a,b; 1995}. Fewer largemouth bass were collected in backwaters in the Colorado River reach between Fish Ford downstream to the confluence with the Green River (Appendix D). No largemouth bass were collected from backwaters in the Green River in any of those years (1979-1993) during Fall sampling for young-of-the-year Colorado squawfish (Appendix E). Few ponds occur in the floodplains along the Green River when compared with the Colorado River. The centrarchid fish species that occurs in the Green River is the green sunfish (Appendix E) and, in some reaches, the smallmouth bass (Salmoides dolomieui). In comparison, numerous floodplain ponds occur along -- the Upper Colorado River and largemouth bass were stocked in this area by the Colorado Division of Wildlife until 1985 and by private pond owners (F. ___ Pfeifer, 1994, Personal Communication). Osmundson (1986) concluded that survival of stocked Colorado squawfish (45 - 145 mm in total length) was significantly reduced from predation by largemouth bass that are over 100 mm in total length. Osmundson also reported that fingerling Colorado squawfish were more susceptible to largemouth bass predation than several common nonnative fishes (e.g., fathead minnows, red shiners, and young-of- the-year green sunfish) found in backwaters of the Upper Colorado River. The 1 argemouth bass i s an effective predator that can have an adverse impact on native fishes (Rivero 1936; Curtis 1942). Langhorst and Marsh (1986) reported that abundant razorback sucker larvae in a Lake Mohave backwater disappeared within 4 weeks after invasion by largemouth bass, green sunfish, bluegill, and some other warmwater fishes. Osmundson (1987) studied the use of ponds along the Colorado River for their potential in rearing Colorado squawfish. He reported that largemouth bass predation by fish over 100 mm TL significantly reduced the survival of stocked squawfish. In fact, squawfish were selected over fathead minnows, red shiners, and young-of-the- year green sunfish. The preference for soft-rayed forage fish (e.g., minnows) over spiny-rayed species (e.g., sunfish) by largemouth bass has been documented in the literature (e.g., Holton 1977; Lewis and Helms 1964). A bioenergetic study completed for the Colorado Division of Wildlife demonstrated that one 12-inch largemouth bass has the predatory effect of 200 redside shiners (Notropis lutrensis) (Appendix D of Martinez 1996). Osmundson (1986) reported that small squawfish were consumed more readily than larger ones by largemouth bass. Immediately after stocking Colorado squawfish in riverside ponds along the Upper Colorado River, largemouth bass completely switched their diets to squawfish that Osmundson related to prey abundance and vulnerability since the squawfish were in a strange environment and were probably stressed from handling prior to stocking. Largemouth bass are not numerous in the riverine habitat of the Colorado River but occupy the quiet backwater areas that are used by larval and juvenile endangered fishes (Miller et al. 1982; Tyus et al. 1982; Valdez et al. 1982). D. Osmundson (1994, Personal Communication) stated that young largemouth bass are commonly found in backwater habitats in late summer but 18