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. " .- , .. f i t I .'-"-'-''"'-='-"''-"""",,,,,,,,,^--.._,,,,",-,,~,._,--,,,......, -----........,,-".. - e as far downstream as Little Hole have not reached the mid-60 F range at which native cyprinids and catostomids spawned below the mouth of the Yampa River. In two of the four summers since impoundment (1964 and 1966), water temperatures in the Green River above the Yampa mouth did not reach this temperature range assumed necessary for spawning, (Vanicek and Kramer, 1969) and no reproduction of any species was observed in this 65-mile stretch of the river proper during these 2 years. The impact of other major environmental changes resulting from closure of the dam, such as alteration of sea- sonal flow pattern and reduction of turbidity, is unknO\'Vll. It appears that the long-range ecological changes in the river have now over- riden any short-term effects the pre-impoundment fish-control opera- tion may have had on fish populations in the Green River below Flam- ing Gorge Dam. CONCLUSIONS. Twenty-one species (9 indigenous, 12 exotic) were collected from the Green River study area in 1963-1966. The rainbow trout was the most abundant species from Flaming Gorge Dam to at least 26 miles downstream; the redside shiner and the speckled dace were the most abundant species in Dinosaur National Monument; and the carp was the most numerous species in the Ouray area below the Monument, The flannelmouth sucker was the most ..yidely distributed fish in the study area, and was especially abundant in the Monument. All species reported in five pre-impoundment surveys were found in post-impoundment years below the confluence of the Green and Yampa Rivers. The closure of Flaming Gorge Dam in November of 1962 has had a major ecological effect on the Green River downstream by alteration of yearly flow and water temperature patterns. Native fishes have nearly disappeared in at least the first 7 miles below the dam, and a reduction in number of native species has resulted as far downstream as the mouth of the Yampa River (65 miles below Flaming Gorge Dam). Below the Yampa, abundance of indigenous and introduced species apparently has not been affected. High discharges of cold water from the dam reduce the summer water temperature significantly which evidently curtails fish reproduction in the 65-milestretch of the Green River from Flaming Gorge Dam to the mouth of the Yampa River. Financial support for this project was provided through the Bureau of Sport Fisheries and Wildlife from funds appropriated under the Colorado River Storage ", Project Act and from the Utah Cooperative Fishery UJDit, a cooperative venture J among the Bureau, Utah State Division of Fish and Game, and Utah State Univer- 313 -"~""-......-.---...~--...~---",,~,~, -'"", '~--'-'''-'-----'-''. ~"""l -#- , , 'I