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EXECUTIVE SUMMARY <br />Winter flows in the middle Green River nursery area consist primarily of releases from <br />Flaming Gorge Dam. Several investigators have hypothesized that winter operations of Flaming <br />Gorge Dam influence age-0 fish survival. As power demands increase, higher flows inundate <br />nursery backwater habitats and transform them into unsuitable flow-through areas. It has been <br />speculated that fluctuating winter flows may dismantle ice cover which acts an insulator, allow <br />the creation of frazil ice, and may result in ice jams that increase river stage and inundate <br />backwaters. As a result, each of these additional stressors may impact overwinter survival of <br />young Colorado pikeminnow by causing the fish to redistribute to more suitable habitats at a <br />time that is very costly bioenergetically. However, the effects of flow fluctuations on overwinter <br />fish survival and nursery habitats have not been demonstrated in the field. <br />Previous studies in the Green River nursery area have shown that population estimates <br />can be made in 20-mile reaches of river, but that accuracy of overwinter survival estimates is <br />suspect, because of unknown immigration and emigration of fish to and from the study area. <br />This study attempted to use capture-recapture procedures to estimate overwinter survival and <br />movement of age-0 Colorado pikeminnow and relate the observed responses to stage fluctuations <br />in the Green River induced by hydropower operations at Flaming Gorge Dam. The following <br />objectives were developed for the study. <br />1) Determine if overwinter survival of age-0 Colorado pikeminnow is affected by winter <br />operations of Flaming Gorge Dam.. <br />2) Determine if backwater habitats are physically affected by fluctuating releases from <br />Flaming Gorge Dam during winter. <br />A-viii