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2. To conserve genetic diversity of wild endangered fish stocks through recovery efforts that will protect or restore viable wild stocks by removing or significantly reducing limiting factors that caused population declines. 3. To maintain genetic diversity in captive-reared endangered fish broodstocks that is similar to the wild stock used as founders. IV. Endangered Fish Stocks in the Upper Colorado River Basin Although thirteen stocks of endangered fishes are currently identified in the Upper Colorado River Basin (Wydoski 1994 a; Table 1), eleven stocks appear to be based on definite spawning aggregations. A stock is defined as a randomly breeding group of individuals that has spatial, temporal, and behavioral integrity from other randomly breeding groups of that same species. This definition applies to multiple stocks within the same river (e.g., humpback chub stocks in Black Rocks and Westwater Canyons of the Colorado River) or a single stock comprising fish from various rivers (e.g., Yampa River stock of Colorado squawfish that contains fish from the Green, White, and Yampa rivers). While the remaining bonytail in the upper basin is listed as a stock, a definite stock (i.e., breeding group of animals) has not been identified to date. In reality, bonytail in the upper basin should not be considered a stock since they are extremely rare in the upper basin with infrequent captures and long time periods between captures. The humpback chub stocks in Desolation-Gray Canyons of the Green River and Cataract Canyon of the Colorado River are in question because they appear to be hybrids with roundtail chubs based on morphological analyses (McElroy and Douglas 1995) and allozyme analyses (W. Starnes, 1995, personal communication). If these two stocks are deleted from the eleven because they are hybrids, nine endangered fish stocks occur in the Upper Basin. The presumptive stock of razorback suckers from the Colorado River arm of Lake Powell should not be considered a stock since actual spawning has not been documented at this location. Razorback sucker larvae have been collected from razorback bar in the Green River near Dinosaur National Monument downstream to the inlet of Lake Powell. The large adult razorbacks (6 in 1980 and 10 in 1981) that were collected in the Colorado River inlet to Lake Powell by Persons and Bulkley (1982) have apparently declined in numbers based on the single adult razorback collected by Valdez (1990) between 1985 and 1988. The Genetics Panel and Recovery Program participants agreed that adult razorback suckers in Lake Powell should be used for broodstock development for the Upper Colorado River Basin and that all razorbacks in Lake Powell may be from one stock (Wydoski 1994b). An attempt to collect wild adult razorback suckers from the San Juan River arm of Lake Powell during the spring of 1995 was unsuccessful (G. Mueller, 1995b, personal communication). A single captive-reared razorback 2