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50.94 m3/s than other flows tested (Pucherelli and Clark 1989). These authors also noted that flows higher than 50.94 - 68.571 m3/s reduced numbers of backwaters during their study. High spring flows may be needed to maximize backwater formation, and gradually decreasing flows may be required to produce good nursery habitats (Pucherelli and Clark 1989). Young Colorado squawfish were sympatric with adult and young of 15 other fish species in backwaters of the Green River, and comprised 6.2% of standing crops (Haines and Tyus, in review). No evidence of resource partitioning between young Colorado squawfish and these fishes was detected when fish densities were contrasted against backwater depth, temperature, size, or substrates; however, the abundance of most species was weakly correlated with the presence of Colorado squawfish (Haines and Tyus, in review). Effects of competition and predation by introduced fishes on growth and survival of young Colorado squawfish has yet to be adequately assessed, but the common use of backwater habitats and foods by young Colorado squawfish and other small introduced fish species (Jacobi and Jacobi 1982; McAda and Tyus 1984; Muth et al., in prep) suggests a potential for interspecific interactions. Karp and Tyus (1990) suggested that growth and survival of young Colorado squawfish may be adversely affected by the aggressive behavior of introduced green sunfish, Le orris cyanellus, red shiner, Notropis lutrensis, and fathead minnow, Pimephales promelas. This may be most acute when increases or decreases in river level reduces the availability of quality backwater habitat and causes resource limitation. There is some indication that abundance of non-native fishes may be adversely affected by periods of high flow, whereas native species appear to be little impacted (Haynes and Muth 1984; Minckley and Meffe 1987; T. Nesler, written communication). However, the hypothesis that native Colorado River fishes exhibit greater tolerance to extreme flooding has not been adequately tested. In the Green River, abundance of most fishes in backwaters was lowest in years of high spring and summer flows (Haines and Tyus, in review). Backwater nursery habitats were influenced by inundation and resuspension of organic material from shorelines during increased flows, and this energy source was important for standing crops of fish food organisms (Grabowski and Hiebert 1989). Backwaters in the Ouray area, where young Colorado squawfish were most abundant, were richer in food than upstream areas studied. Reduced water-level fluctuations in that area resulted in more stable backwater habitat, and possibly reduced the export of nutrients and food (Grabowski and Hiebert 1989). Juveniles Little is known about the habitat requirements of juvenile Colorado squawfish, but they have been captured in a variety of habitats including backwaters, shorelines, and flooded bottomlands. Although rare, juvenile Colorado squawfish are most abundant in the lower Green River (Tyus et al. 1987), and downstream drift of larvae suggests that a long-distance upstream movement by juveniles is needed to repopulate upstream areas. Such movement probably occurs during the late juvenile or early adult stage, because only large-sized fish are found in the upper Yampa River, and the highest concentration of juveniles is found in the lower Green river (Tyus 1986; Tyus et al. 1987). Evidence of predation by non-native fishes in both artificial and natural environments suggests that this factor may impact the survival of juvenile 20