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<br />250C, a temperature in which optimal growth occurs {Black and Bulkley <br />1985a, 1985b}. Our findings indicated that most fishes used average <br />backwater temperatures within years, but were most abundant in warmer <br />years. Young Colorado squawfish did not display temperature preferences <br />when backwaters averaged about 190C (lower Green River), but avoided cold <br />backwaters {<IOOC} in the upper Green River. Tyus and Haines {In Review} <br />demonstrated that growth of young Colorado squawfish was not affected by <br />cooler temperatures of the upper Green River, and this suggests that <br />other environmental conditions compensated for cooler than optimal water <br />conditions. <br />No evidence of habitat partitioning among Colorado squawfish, red <br />shiner and fathead minnow was evident for backwater temperature, maximum <br />depth or size. The greatest degree of habitat segregation was found <br />between Colorado squawfish and native suckers, the squawfish utilizing <br />slightly warmer and deeper backwaters. Others also have observed little <br />or no habitat segregation between young Colorado squawfish and other <br />sympatric species (C. M. McAda, L. R. Kaeding; written communication). <br />Backwaters that contained Colorado squawfish also contained other <br />fishes, and this may just be reflective of more productive habitat, i.e. <br />backwaters that were better suited for fish life than others, regardless <br />of species. <br />Although we did not detect effects of other species on the abundance <br />of young Colorado squawfish, Karp and Tyus (1990) reported aggressive <br />behavior toward Colorado squawfish by introduced species in aquaria, and <br />speculated that such interactions may occur in nature. Young Colorado <br />squawfish may also be prey for larger fish that enter backwaters, e.g., <br /> <br />11 <br />