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<br />red shiner, green sunfish, juvenile Colorado squawfish, channel catfish <br />and black bullhead. Osmundson (1987) found predation on squawfish by <br />largemouth bass, green sunfish and black bullhead in small, off-channel <br />ponds. In our study, larger predators could easily have escaped from <br />backwaters during seining and thus avoided our detection. One large <br />predator could distort backwater fish population structure and such an <br />effect could have biased our results. <br />Many introduced fishes co-occurred in backwaters with young Colorado <br />squawfish, and we presume that flows benefiting native fishes may also <br />benefit the introduced fishes. However, native fishes of the Southwest <br />may be more resistant to natural flood events than species introduced <br />from more mesic environments (Minckley and Meffe 1987). We did not <br />detect this phenomenon, but our correlations of maximum spring discharge <br />and autumn species abundance investigated long-term, rather than <br />instantaneous effects of flooding. Our sampling design did not permit a <br />separation of potential effects of maximum discharge from mean August <br />flows, and the occurrence of these two events were highly correlated (r = <br />0.93, P < 0.01) during this study. In addition, comparison of <br />hydrologic events in a large regulated river such as the Green River with <br />smaller, more natural desert streams, may not be appropriate. <br />Introduced species predominated in nursery habitats of the <br />endangered Colorado squawfish. The proliferation of these fishes has <br />resulted in a new fauna whose trophic structure and other <br />interrelationships are poorly known. Our macrohabitat evaluation of <br />certain environmental parameters did not detect resource partitioning <br />between Colorado squawfish and the most abundant non-native fishes. <br /> <br />12 <br />