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• • project in the early 1960's. After closure of the outlet structure, razor- back suckers did not occur in the Green River below the reservoir to the mouth of the Yampa River, although they could still be found from Echo Park to Ouray, Utah in the Green River. In 1970, Holden (1974) collected 10 to 15 razorback suckers from the mouth of the Yampa River. Seethaler and McAda (1974) also collected razorback suckers in Echo Park area. Although authentic razorback sucker collections do not exist for several likely tributaries of the Colorado River (in Colorado) i.e., the White, San Juan and Dolores Rivers, it is docu- mented that they occurred in the Gunnison River upstream to Delta, Colorado, in the Colorado River upstream to DeBeque, Colorado, in the Green River upstream to the Flaming Gorge Reservoir site, in the Yampa River near its mouth, and at one unnamed location in the Animas River. There is doubt that razorback suckers were ever abundant in the Yampa and Green Rivers but general agreement that they have declined to a point of extreme rarity in the Gunnison and Colorado Rivers, as well as the entire upper Colorado River basin. Historical distribution of the bonytail chub was probably similar to that of the razorback sucker, yet somewhat more difficult to identify because the names "roundtail chub" and "bonytail chub" were used synonomously in the early literature. Holden and Stalnaker (1970) partially resolved the taxonomic confusion in the genus Gila by elevating Gila robusta subspecies to separate species, Gila elegans, bonytail chub, and Gila robusta, roundtail chub. Pre-impoundment studies for Flaming Gorge Reservoir by Gaufin et al. (1960) and Banks (1964) revealed bonytail chubs in the main channel of the Green River and in the deep pool near Hideout Canyon. From 1957 to 1966, Vanicek and Kramer (1969) collected 67 adult bonytail chubs from the Green River between Flaming Gorge and the mouth of the Yampa River. Strong year - 5 -