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15 fed, and only smaller individuals with low lipid content died when starved 210 days at 3-4 °C. Thompson found that age-0 fish actively foraged in laboratory and field conditions, and it is assumed that healthy young survived the winters under 1985-1989 flow conditions (Tyus and Haines 1991). Late summer and autumn are critical periods for growth and survival of young Colorado squawfish, and historical flows in the Green River system at this time are predictably low. Juvenile temperature tests showed that preferred temperatures ranged from 21.9-27.6 °C. The most preferred temperature for juveniles and adults was estimated at 24.6 °C. Temperatures near 24 °C also are best for optimal development and growth of young (Miller et al. 1982b). Tyus et al. (1987) noted that abundance and growth of young Colorado squawfish in the Green River were negatively correlated with high, cooler late summer and autumn flows. During the late summer and autumn, catch and growth were highest in average flow years of 1979 and 1980 and lowest in abnormally high flow years of 1983 and 1984 (Tyus et al. 1987). In 1983 and 1984, unusually high releases from Flaming Gorge Dam in the late summer and autumn inundated backwater nursery areas, and survivorship of young Colorado squawfish was low. These relationships suggest that flows promoting growth and survival of small Colorado squawfish vary with time of year and that both reproduction and survival are highest in years when hydrographs more closely approximated natural flow conditions. This presumably relates to the availability of nursery backwater habitat in autumn (Tyus and Haines 1991). A summer flow range of about 1,100-1,800 cfs maximized the number of backwaters in the upper Green River basin on aerial photography and videography (Pucherelli and Clark 1989). These authors also noted that flows above 1,800 cfs reduced numbers of backwaters at Island Park and Jensen 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). Effects of competition and predation by introduced fish on growth and survival of young Colorado squawfish have yet to be adequately assessed, but the common use of backwater habitats and foods by young Colorado squawfish and small introduced fish species (e.g., channel catfish; green sunfish, Le orris cvanellus; red shiner, No~pis lutrensis (Jacobi and Jacobi 1982; McAda and Tyus 1984; Muth et al., in prep.)) suggests a potential for negative interactions. Karp and Tyus (1990b) suggested that growth and survival of young Colorado squawfish may be adversely affected by the aggressive behavior of introduced green sunfi"sh, red shiner, and fathead minnow, Pimephales aromelas. This may be most acute when increases or decreases in river level reduces the availability of quality backwater habitat. There is some indication that abundance of nonnative fish may be adversely affected by periods of high flow (Haynes and Muth 1984; Minckley and Meffe 1987; T. Kesler, written communication). Still, the hypothesis that native Colorado River fish exhibit greater tolerance to extreme flooding was not adequately tested. In the Green River, abundance of Colorado squawfish and red shiner in backwaters was lowest in years of high summer flows (Haines and Tyus 1990).