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. .. ,- .. .. . ~._.....~--~~~.._---,.__. '-~--'--e ~ i 1 found in Flaming Gorge Reservoir basin (McDonald and Dotson, 1960). Mountain whitefish and humpback clmhs were also reported taken from the reservoir basin in 1959 (Gaufio.. Smith, and Dotson, 1960). The collection of humpback chubs in the study area in pre-impound- ment years has not been substantiated. Azevedo (unpublished fishery management report, Bureau Sport Fisheries aad Wildlife) reported taking two specimens in Split Mountain Canyun on July 23, 1962. Closer examination of these fish by Utah Cooperative Fishery Unit personnel, however, indicated that they were the bonytail fonn of the Colorado chub. Hagen and Banks (1963) reported collecting two hump- back chubs in Echo Park in October 1961, and ooe specimen at Echo Park on September 17, 1962. In an earlier report, however, Hagen (1962) stated that the identification of the two 1961 fish as humpback chubs was not positive though both had prominenahumps and enlarged fins. Banks (1964) included the 1961 and 1962 collections cited above in his thesis, which (for the purpose of the present study) was used as the latest and presumably most accurate analysis of the earlier reports. Apparently subsequent examination revealed that none of the three specimens were humpback chubs because]lanks (1964) did not include this species in his lists for the same collections in which they had appeared as cited by Hagen (1962) and Hagen and Banks (1963). ,I 1 I I DISCUSSION. A valid comparison between pre- and post-impound- ment fish populations is difficult since post-impoundment sampling efforts were much more intensive than the p~impoundment efforts. In general, species composition in Flaming GoIge Reservoir basin prior to impoundment was very similar to that in Dinosaur National Monument in both pre- and post-impoundment collections. Though few pre-impoundment collections were made from the damsite to Browns Park (26 miles), we made the assumption that the species composition in this area before impoundment was similar to that reported in the reservoir basin before 1963. If this assumption is cor- rect, the most notable changes in species composition is this stretch of river after impoundment have been the disappearance of Colorado .. squawfish, Colorado chub, humpback chub, and hllmpback sucker, and the appearance of rainbow trout. Species composition in the river from Browns Park to Echo Park has been altered to a lesser degree, but composition of fish populations is still considerably different from those present at Echo Park. Fish species composition has not changed in the Green River down- stream from its confluence with the Yampa. All native species known 311 - '--~---"--'_.-'----:'---'-'''-'-''~'' ~~4~ '_:_"_"';'~~_"'"'""__'__~_"'"":"__~.____' ~ ~ ____...--r<_........,..._,___+__~~~,_' _,~ ~..._':-"_ ~ " , "" ~-,--_ .........-.00