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<br />remains high (Thompson 1984), and it is unknown whether reduced sediment <br />levels as a result of the Aspinall Unit have affected the endangered fishes in <br />the Colorado River. <br />Streamflow <br />The most important change resulting from construction of the Aspinall <br />Unit has been the reduction of spring flows in the Gunnison and Colorado <br />rivers. Spring flow is the most important annual event that shapes the <br />channel, and thus the habitat of the two rivers. High spring flows create and <br />maintain the braided channels that provide a variety of important habitats for <br />the endangered fishes. Reduction of high spring flows allows the river to <br />gradually simplify its channel--side channels and backwaters fill with silt <br />and become unusable by the native fishes, sand bars are invaded by tamarisk <br />which stabilizes them and makes them resistant to erosion, and gravel-cobble <br />substrates become armored or imbedded in silt which reduces their utility as <br />spawning substrate. <br />Colorado squawfish <br />Osmundson and Kaeding (1990) showed that radiotagged Colorado squawfish <br />selected complex-habitat areas over simple-habitat areas in the upper Colorado <br />River. They divided their 33-mile study area into 0.4-mile segments and <br />categorized each segment as either complex or simple depending upon whether <br />islands, backwaters, or side channels were present or absent. Their study <br />area contained equal numbers of simple and complex segments, but radiotagged <br />Colorado squawfish were most often located in complex-channel segments. Of a <br />total of 428 observations of radiotagged Colorado squawfish, 85~ of spring <br />locations, 71~ of summer locations, and 63~ of winter locations were in <br />24 <br />