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I I I I I I I I I I I I I I I I I I I these changes in flow than the other large river fishes. The reduction in bony tail populations in the upper Colorado River probably occurred prior to those in the Green River since none have been coll ected si nce the early 1900's. This reduction is probably related to reductions in flow (CRFRT 1982b) since the Colorado River was reduced in flow before the Green River (Joseph et al 1977). Razorback Sucker Distribution, Abundance, and Ecology: The razorback sucker is a Candidate Species for listing under the Endangered Species Act. It has been proposed for listing and may be again in the near future. It was originally found in the main channel s and larger tributaries of the Colorado River system. It is presently found in large numbers in several lower basin reservoirs and associated riverine areas, and is found in the upper basin in the Green, Colorado, and San Juan rivers, as well as larger tributaries. In the upper Colorado River it is found from Lake Powell to near Rifle, Colorado, as well as in the Gunnison River below Delta, Colorado (Valdez et al 1982; Kidd 1977). Concentrations have recently been found in flooded ground pits near Grand Junction during high water, al though they are seldom found in such numbers at other times of the year (Wick et al 1982). The population in the De Beque area has not been well studied, and only a few specimens have been found in this area, although large con- centrations were noted several years ago (Kidd 1977; Sealing 1983). This population is cut off from other populations by the diversion dams between De Beque and Grand Junction. Adult razorbacks are usually collected in flooded gravel pits or nearby river locations in the Colorado River. In the Green River they are generally collected in backwaters. These collections are ordinarily - 28 -