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there was a tendency for Colorado squawfish to be less common in small, shallow backwaters, or in cool backwaters. These same general observations were made by Haines and Tyus (1990). These observations are somewhat contradictory since small shallow backwaters are often the warmest backwaters. However, these data suggest that some minimum size or minimum depth is necessary for Colorado squawfish to use a backwater. Besides the obvious preference for backwater habitats, it is difficult to break down habitat preferences of YOY Colorado squawfish any further than that. More detailed studies currently being conducted by the Utah Division of Wildlife Resources may be able to provide more information about their preferences. Bates et al. (1993) found no significant difference in backwater use based on temperature using part of the data presented here. However, they did find a slight positive relationship between CPE and backwater temperature. McAda and Tyus (1984) sampled the same backwater over several days and found a significant positive correlation between CPE of Colorado squawfish and water temperature in the backwater. They speculated that some fish moved into the backwater as it warmed during the day and moved out of the backwater as it cooled at night. However, Colorado squawfish were always present in the backwater and CPE was always higher there than in the nearby river channel. They found no significant relationship in several other backwaters sampled. Analysis of temperature preferences using ISMP data is complicated because each backwater is only sampled once and Colorado squawfish abundance is different in every~backwater sampled. Although difficult to show with survey data such as ISMP, Colorado squawfish preference for warmer water is real. In the laboratory, yearling Colorado squawfish acclimated to a variety of temperatures all preferred water warmer than 20°C; they grew fastest in water held at 25°C (Black and Bulkley 1,985a, 1985b). ~mpatric S ep CIeS Nonnative species were the most common fishes collected during ISMP, with the three most common species being fathead minnow, red shiner, and sand shiner. These three species are typically the most common fishes collected by all investigators in the upper basin (e.g. Tyus et al. 1982, 1987; Valdez et al. 1982; Archer et al. 1985; Valdez 1990). Distribution patterns for these species are basically the same as reported by these other investigators, although relative abundance has fluctuated over time and space. In the Colorado River, these common nonnative fishes have apparently increased their abundance over the course of the monitoring program. The first year of the program (1986) had the highest runoff of all the years observed and the highest percentage of native fishes in the catch. Spring runoff has been considerably reduced since then and the percentage of nonnative fishes has increased. Several researchers (McAda and Kaeding 1989a; Osmundson and Kaeding 1991; Valdez 1990) have suggested that extended periods of low runoff allow populations of nonnative fishes to increase in Colorado squawfish nursery areas. Muth and Nesler (1993) found an earlier spawning period and higher CPE for the three most common nonnative fishes to be correlated with low peak discharge in the Yampa River. The large numbers of introduced species have led many investigators to hypothesize that nonnative fishes may have negative affects on small Colorado squawfish through predation or competition. However, demonstration of competition in field studies is problematic because controlled evaluations are difficult in that environment. Documentation of predation is also difficult because small Colorado squawfish are rare in many locations. These difficulties apply to ISMP data as well. Of ten significant relationships between CPE of one of these common introduced species with CPE of i Colorado squawfish, only one was negative. Of the 55 non-significant correlations, most were 22