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7 <br />mens, however, were collected in 1963 below Flaming Gorge Dam in the present <br />study,.,but gone was:found,during 1964-1966. This species was apparently very <br />-rare before the fish control operation and closure of Flaming Gorge Dam and <br />remains rare in this part of the Green River. The humpback chub" or a closely- <br />related Gila form, appears to be relatively common in Lake Powell and below <br />Glen Canyon Dam at present, however. The most abundant species in the first <br />50 miles below Flaming Gorge Dam is the introduced rainbow trout (Salmo aird- <br />neri). <br />All native forms except the humpback sucker have reproduced successfully <br />in the Green River below the mouth of the Yampa River in all post-impoundment <br />years. Time of spawning has varied with the water temperature patterns and year- <br />class strengths of all species have fluctuated for reasons yet unknown. Growth <br />-- rates of Colorado squawfi-sh and-Colorado chubs were studied in detail and have <br />decreased greatly since the closure of the dam. This was apparently a direct <br />response to altered water temperature patterns. <br />Species composition of the invertebrate fauna in 1965 was similar to that <br />reported in pre-impoundment years from Carr Ranch (43 miles below the dam) to <br />, >=the-end of the study, area a-t -Ourayi --Utah. In the 43-mile stretch between <br />Flaming Gorge Dam and Carr Ranch, however, the number of species decreased and <br />the standing crop increased with the highest densities present within 7 miles <br />of the dam. These changes were related to lowered water temperatures and re- <br />duced turbidity in this area. Dominant forms at present are major trout-food <br />organisms. In the entire study area, nine forms of invertebrates reported <br />prior to September,:1962, were-not--collected during the present study but all <br />are found elsewhere. Ten groups not previously reported in pre-impoundment <br />surveys were collected. <br />Changes in the ecology of the river below Flaming Gorge Dam are the <br />primary factors currently affecting the present distribution and abundance of <br />,u A--,LL---,t-in igenous-fishes--arid inverterbrates -in=-the Green River. Any effects of rotenone <br />in Dinosaur National Monument during the fish control operation in 1962 were <br />temporary as indicated by the presence of all previously-reported fish species <br />in this area in 1963. The observed reproductive success and presence ofc-all <br />species below the confluence of the Green and Yampa Rivers suggests that the <br />ecological requirements of all species, with the possible exception of the <br />humpback-sucker, are-being met"at the present time in the Green River below <br />the mouth of the Yampa. <br />9