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Therefore, tha historical distribution of Gila ~pha probably included most of the larger, swift-avatar canyons on the Colorado and Green rivers above Lake Mead, and two Graea River tributaries, the Yampa and White rivers. The absence of reliable data makes it difficult to adequately assess pre-1950 humpback chub abundance. Their abundance in the canyon areas listed above was usually limited, although they were common is one or two particular spots within those areas (Smith 1960; Holden and Stalnaker 1975; Kidd 1977; Seethaler et al. 1976). Occurrence of humpback chub bones in caves used by Indians suggests a fair abundance at one time in the area near Hoover Dam (Miller 1955). However, the general impression is that during historical time, this species-may have bees uncommon when compared to other endemic fishes. Present Distribution and Abundance - Available data indicate that several major changes have occurred in humpback chub populations. Humpback chubs were eliminated from the Green River above the mouth of the Yampa River in Colorado, Utah, and Wyoming whey Flaming Gorge Dam became operational in 1962 (Vanicek et al. 1970). Humpback chubs were common in fishery samples from La1ce Powell soon after closure in the 1960'x, but they have not been collected during the last few years (personal communication, Dale Hepworth, Utah Division of Wildlife Resources). The cold tailwaters of Glen Canyon Dam (Lake Powell) have apparently caused major reductions is both distribution and abundance of humpback chubs in Marble and Grand canyons (Hinckley 1973; Holden and Stalnaker 1975; Suttkus et al. 1976). Recent researchers in Marble and Grand canyons have found humpback chubs distributed from River Mile 27 to River Mile 108, with a concentration occurring in and near the mouth of the Little Colorado River (Suttkus et al. 1976;~personal communica- tion, C. Hinckley, Museum of Northern Arizona). ~ C. Hinckley (1977) recently recorded humpback chubs 13 ion upstream is the Little Colorado 81ver. Due to the recent discovery of humpback chub populations in Desolation Canyon and the Black Rocks area, no population changes have been documented. Recent collections in the White River (Anonymous 1977) and the Colorado 4