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that they had disappeared from this area by 1937. Reservoir impoundments apparently do not affect adult razorback suckers as much as they affect other endemic species. When Lakes Mohave and Mead were formed on the Colorado River, the Colorado squawfish, bonytail chub, and humpback chub were drastically reduced in numbers, but the razorback sucker remained abundant in Lake Mead and common in Lake Mohave (Wallis 1951). Jonez and Sumner (1954) found many razorback suckers in the Colorado River below Davis Dam, but none have been reported from this region recently (Minckley 1973-. As late as the 1940's, razorback suckers supported a commercial fishery in Arizona. One fisherman harvested some 5.4 metric tons from Sahuaro Lake, an impoundment on the Salt River, in 1949 (Hubbs and Miller 1953-. However, no razorback suckers were found when Sahuaro Lake was drained in 1966 (Minckley and Deacon 1968). In fact, the species has apparently disappeared from the entire Gila River arm of the lower Colorado River basin (Minckley 1973-. Lakes Havasu, Mead, and Mojave still contain razorback suckers, but only mature fish are found, indicating that successful reproduction has been greatly curtailed or does not occur. The razorback sucker appears to be more widespread in the upper Colorado River basin, but has never been reported to be abundant there (Banks 1964; Deacon 1968; Vanicek et al. 1970; Miller 1972; Stalnaker and Holden 1973; Holden et al. 1974; Holden and Stalnaker 1975a,1975b). There are few early reports about the abundance of the razorback sucker in the upper basin. Jordan (1891) wrote that razorback suckers were abundant in the area, but documentation is limited. The inacces- sibility of the canyon areas and the violent turbulence of the river made sampling of fish difficult, and early efforts were cursory at best. Vanicek et al. (1970) reported the elimination of razorback suckers from the tailwaters of Flaming Gorge Reservoir, but theorized that they were uncommon there even before the reser- voir was impounded. Holden and Stalnaker (1975b) found scattered individuals throughout most of the upper basin and discovered concentrations of 10 to 15 fish in the mouth of the Yampa River in March and November 1970. Razorback suckers were reported recently in a pond separated from the lower San Juan River near Bluff, Utah (N. Armentrout, personal com- munication, but their abundance was not determined. During the present investigation, razorback suckers were found to be most common, though never numer- ous, at two locations-the mouth of the Yampa River at station 3 (Echo Park) during early spring, and the Colorado River at station 8 (Walker Wildlife Area) throughout the year. Occasional razorback suckers were also found at station 3 during the fall and at sta- tions 4 and 7 (Table 1-. Table 1. Numbers of razorback suckers collected from the upper Colorado River basin, by dates and location, August 1974-November 1976 Year and stations Dates No. collectedb 1974 Walker Wildlife Area (8) 24 Oct.-1 Nov. 22 Echo Park 131 14-18 Nov. 3 Sand Wash (7) 9-12 Dec. 1 1975 Walker Wildlife Area (8) 3-10 Apr. 11 24-28 May 24 (8) 15-17 June 3 4-9 Oct. 9 Island Park (4) 4-16 Apr. 2 29 Oct.-1 Nov. 1 Echo Park (3) 1-22 May 24 (1) 14-16 Nov. 1 1976 Echo Park (3) 2-5 May 1 Walker Wildlife Area (8) 12-16 Apr. 5 sSee Fig. 1 for locations of stations. bNumbers in parentheses indicate number of tagged recap- turesincluded in total. The razorback suckers moved into the area of the confluence of the Yampa and Green rivers (Echo Park; station 3) in late fall and apparently remained there through the winter (Table 2-. Although considerable sampling was done in the lower sections of the Yampa River during summer and early fall, no razorback suckers were collected during that period in 1975 or 1976. Nor were razorback suckers collected farther than 2 km upstream in the Yampa River, despite con- siderable collecting effort at our stations 1 and 2 (Table 3). However, a single razorback sucker was col- lected at station 1 in July 1979 by investigators from Colorado State University (E. Wick, personal com- munication. Sampling was not possible during winter because of ice cover and the inaccessibility of the canyon areas. Some razorback suckers probably remained in the area over winter, where they were joined the following spring (in late April) by other fish moving from the Green River into the mouth of the Yampa. A female razorback sucker, captured and tagged in the Green River at station 4, was recaptured 2 weeks later at the mouth of the Yampa River, 21 km upstream. Inasmuch as the fish was ripe when recap- tured, it may have been collected during a spawning migration. Razorback suckers apparently leave the mouth of the Yampa River in late spring or early summer as streamflow decreases and water temperature in- creases. A total of 23 razorback suckers were collected at