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from home ranges. In the Green River, adult Colorado pikeminnow used the following habitats in rank order: slow runs, slackwaters, eddies, and backwaters, where depths averaged 2.5 to 4.5 feet and velocities were 0 to 1.0 fps. In the unregulated Yampa ~ River, the fish occupied off-channel backwater and embayment habitats that were probably sources of food organisms (Wick and Hawkins 1989). The fish were found in depths that varied between habitats, averaging 2 to 3.5 feet in backwaters, embayments and runs, and 5 to 9.5 feet in eddies (Wick and Hawkins 1989). Movement of the fish into backwater habitats was attributed, in part, to feeding (Wick and Hawkins 1989). Winter habitat use was similar in the 15-Mile Reach, where pools ~ and runs were used 77-95% of the time (Osmundson et al. 1995). In spring and early summer, when rivers are rising; but prior to spawning migration, habitat use by adult Colorado pikeminnow depends on water conditions. The fish were most often located in seasonally-inundated shorelines, including backwaters or ~ bottomlands (Tyus 1990). Radiotracking data indicated use of shoreline backwater habitat in a low-flow year (1981) and use of flooded bottomlands during ahigh-flow year (1983) (Tyus and Karp 1989). Flooded shorelines were also used by adult Colorado pikeminnow during the iwo high-flow years, 1983 and 1984 (Tyus et al. 1987). Seasonally-flooded bottoms were used from late April to May of 1985 and 1987, during ~ flow events that represent average annual high flow events (i.e., 226 - 283 m3/s). Wick et al. (1983) noted in 1982 (an average-flow year), that adult Colorado pikeminnow used flooded shoreline areas in spring, but moved to backwater habitats as the river level dropped. ~ Hab~at use also is influenced by flow regime. Under moderate flow conditions, adults in the UCR were found in backwaters, eddies, and pools 90% of the time, and in runs only 10% of the time (Osmundson et al. 1995). When flows were low, adu~s were found in runs 97% of the time. The apparent shift in preference is probably the result of changes in habitat availability caused by changes in flow (e.g., inundated gravel pits simply do not exist at low flow; Osmundson et al. 1995). The availability of inundated gravel pits in the UCR can create a distorted view of the general habitat requirements for the species. In the UCR, Valdez et al. (1982) reported that the average water depth where adults were captured was about 6 ft, which is much deeper than the average depth recorded for adults in the Green River. The ~ difference probably reflects the importance of inundated gravel pits, which are present in the UCR, but not in the Green River. Adult Colorado pikeminnow are piscivorous (Vanicek 1967), but will consume other prey (Beckman 1953, USFWS 1991). Their na#ural prey were native suckers and ~ chubs, which are readily consumed. They also will consume nonnatives, but occasionally with deleterious consequences; there are several accounts of pikeminnow choking on the spines of channel catfish (Vanicek 1967, McAda 1983, Pimental et al. 1985, Quarterone 1993). 11