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The largest existing population of bonytail chub is found in Lake Mohave in the Lower Basin. The bonytail chub have been artifically propagated in the hatchery where they have produced offspring. At this date it appears doubtful that the bonytail chub will survive without intensive species management. Razorback suckers, like the bonytail, are rare in the Upper Basin. However, a few razorbacks were observed at spawning time near the Ashley Creek confluence on the Green River, the Walker Wildlife Area, and a gravel pit on the Colorado River near Clifton, Colorado. Reproduction seems to be a major problem and no young razorback have been recorded from the Upper Colorado River in recent years. Almost all fish observed in this study were old individuals. Competition with exotics appears to be a serious problem for the razorback, although only limited data collected during this study and observations recorded in Lower Basin work supports that conclusion. Again, the survival of razorbacks will proba- bly require some intensive species management. Recommendations Any program developed to protect the rare Colorado River endemic fishes should focus on three concerns. First, the protection of existing spawning and rearing areas; second, the continued development of habitat improvement areas with associated facilities to ensure propagation and management of the species, in case natural production fails; and third, protection and maintenance of migration routes for Colorado squawfish to ensure access to spawning, feeding, and rearing areas. A Colorado River endangered fish monitoring program which would evaluate recommended river flow requirements and the use of specific natural and man-made areas by endemic fishes is required. These studies should be reduced in scope to verify flow needs and assess existing reproductive success on known spawning areas. Further, the studies would help arrive at some practical solutions for the propagation of rare fishes which may need intensive management. Potential problems relating to hybridization of chubs may also require monitoring. Minimum instantaneous flow requirements at selected sites for the Colorado squawfish and humpback chub are presented in the table on the following page. These minimums are based upon computer simulation, physical habitat modeling, and actual flow for 1979-81. The flow of the river at these selected points should not fall below the required level to ensure the present levels of reproductive success. However, it should be noted that the Colorado squawfish populations in many areas are decreasing under present conditions and additional measures will need to be implemented to stabilize or increase the numbers of this endangered species. • Any future water development program in the Colorado River system should be compatible with the known requirements of the endangered Colo- rado River fishes. The Fish and Wildlife Service is presently developing a conservation plan to provide guidance for future management of the endangered Colorado River fishes. We believe that eventually a manage- ment program including habitat improvement, a hatchery, and stocking will be required for some, if not all, of these endangered fishes. 2