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<br />Average macroinvertebrate abundance in backwaters increased progressively <br />downstream within the study reach, although variability was high among the <br />several backwaters sampled at a site. Total riverine benthos averaged 599, <br />359, and 461m2 in 1988 at Island Park, Jensen, and Ouray respectively. <br />Riverine substrate at Ouray was mostly shifting sand. In backwaters, total <br />benthos in the 1988 averaged 2,411, 2,111, and 3,326/m2 for Island Park, <br />Jensen, and Ouray, respectively. In many samples, chironomid larvae comprised <br />over 90 percent of the benthic fauna. <br /> <br />Benthic algae and detritus, although not sampled in this study, probably <br />contribute to the food base for the collector-gatherer chironomid larvae and <br />the other grazing macroinvertebrates. It comprised a large portion of the <br />stomach contents of the young suckers collected. Predatory chironomid larvae, <br />although few in number in the backwaters sampled, likely prey on the grazing <br />chironomids. Food web interactions at this lower trophic level may result in <br />nutrient recycling within some Green River backwaters. <br /> <br />Food habit studies of 16 species of native and nonnative fish collected from <br />backwaters, indicated some dietary overlap due to heavy utilization of <br />chironomid larvae by some young fish <20 mm TL. The 14 Colorado squawfish <20 <br />mm Tl collected in 1987 and 1988 consumed mostly chironomid larvae, while <br />Colorado squawfish >20 mm TL showed evidence of piscivory, but continued to <br />consume chronomid larvae. As the Colorado squawfish grow and include larval <br />fishes, primarily red shiner, in their diet, along with chironomid larvae, <br />dietary overlap with other fish species diminishes because of the expanded <br />food resource. The stomachs of some young fish, such as the native suckers, <br />contained mostly algae. Few fish species other than Colorado squawfish and <br /> <br />6 <br />