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.. . .. . ... .. 55 ur AH ACADEMY PROCEEDINGS, VOL. 51, PART 2, 1974 and other lower basin reservoirs. Spawning has been observed, but no juveniles have been found. Upper basin populations appear much lower than in the late 1800s, and no large reservoir populations have been noted. Holden (1973) found only 53 humpback suckers in four summers of collecting in the upper basin and listed them as rare. In Utah they are found in the Green and Colorado Rivers, and a few have been reported from Lake Powell. Factors Influencing Decline: Similar to other large river fishes of the Colorado basin, habitat destruction through dam construction, water diversion, and competition with introduced species are considered major decimating factors for humpback suckers. This species has not fared well during the 20th century while man has been altering its habitat. Recent Studies Holden (1973) documented the abundance lInd distribution of the Color~do squawfish, bony tail chub, humpback chub, and humpback sucker in the Upper Colorado basin. Adults of these species are currently being sought to obtain brood stocks for artificial propagation and eventual restocking of suitable habitats in the lower basin.2 Squawfish and humpback suckers are presently being held in the Willow Beach National Fish Hatchery. At this date over 3,500 juvenile humpback suckers and 6,000-7,000 squaw fish have been hatched from these fish. Utah State University has initiated a radio telemetry study of humpback suckers and squawfish in Dinosaur National Monument. The Lower Colorado River Drainage Recovery Team is funding a life history study of humpback suckers in Lake Mohave. .. Recommendations Ut.ah populations of the four endangered Colorado River system species should be monitored frequently. Monitoring of the Desolation Canyon area is critical as all four species are found and apparently reproduce there. Spawning sites of the four species in the Green River should be elucidated and protected. tife history studies are recommended to determine require- ments for spawning and juvenile survival. Recovery attempts should be made or continued for the four species, as should determinations of suit. able habitat for artificially reared individuals. The culture program could allow for hybridization studies to help clarify the taxonomy of the Gila .. 2. Lower Colorado River Drainage System Endangered Fishes Recovery Team, Gail Kobetich, Fish and Wildlife Service, Parker, Arizona, Chairman. ., --- ~ .. . t. , .