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varies from site to site. Some populations seem to be pure, but others contain a high percentage of hybrids. Prospects for the Future Because of its more widespread distribution and greater abundance, and its utilization of artificially created habitat, the razorback sucker seems to have a more hopeful future than do the three species pre- viously discussed. The problem of successful repro- duction must be solved before the continued existence can be assured and increased abundance can be effec- ted. Adult razorback suckers flourish in reservoirs and pond type environments, but the young have not been found in such environments. It would be most important to know what the optimum spawning condi- tions are, in regard to depth, velocity, and sub- strate. It will also be important to learn what associated non-native fishes are least harmful and what species are most harmful to successful reproduc- tion. 1982 Studies by California Fish and Game Department biologists in Senator Wash Reservoir, California, and by biologists of the University of Nevada's Lake Mead Laboratory in Lake Mohave, have provided some docu- mentation on the spawning of razorback suckers and the role of non-native fish predation as a limiting factor for successful reproduction. Razorback suckers were observed to spawn over rocky-gravel bottems along lake shores. The spawning attracted many non-native fishes such as bass, sun- fish, carp, and channel catfish which rapidly con- sumed the newly spawned eggs. In Senator Wash Reservoir, predation evidently was completely effec- tive in suppressing reproductive success -- no young razorback suckers have yet been found. In Lake Mohave, some eggs do escape predation and a few newly hatched fish have been found. More intensive samp- ling of Lake Mohave has revealed the abundance of razorback suckers is much greater than previously thought and the wide range of sizes represented in collections indicate that past reproduction has been successful, at least in some years. Artificial propagation of razorback suckers has been conducted for several years at the Willow Beach Federal Hatchery, Arizona. Populations could be main- tained in reservoirs by stocking fish reared in a hatchery, but if reproduction is not successful in a reservoir or a section of a river, reproduction by stocked razorback suckers cannot be expected. Because the razorback sucker has not yet been listed as endangered or threatened by the federal government, it has not been eligible for federally funded projects on endangered species, and has re- ceived much less attention than have the squawfish and humpback chub. It would be useful, for a better understanding of the species, to document its occur- rence in all off-channel pond habitats, correlating the abundance of razorback suckers with habitat char- acteristics such as size, shape, depths, and associa- ted fish species. An analysis of the common demoni- nators of the factors that favor the success of the species could then be made. If this were done, future man-made modifications might be designed to benefit the razorback sucker and perhaps the squawfish. UPDATE The aggregations of razorback suckers noted every spring in the Walter Walker pond and the Clif- ton gravel pond along the Colorado River near Grand Junction can now be interpreted as fish seeking these pond type environments for spawning. The problem is, however, that these man-made environments also harbor the same array of non-native fish predators observed consuming razorback sucker eggs in the lower basin reservoirs. The recovery of the razorback sucker will depend on eliminating or controlling the num- bers of non-native fishes in preferred spawning sites or constructing sites that would fill during the run- off period, allowing spawning and rearing of the newly hatched razorback suckers, and then drain during low flow to prevent the establishment of non-native fishes. The artificial propagation program for the razorback sucker is now carried out at the Dexter, New Mexico, National Hatchery. Large numbers of hatchery-produced fish were stocked into the Salt, Verde, and Gila rivers of Arizona in 1981 and 1982, and future introductions are planned for the San Juan River of New Mexico. 27