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1 5. defines hatchery facilities required to meet identified propagation needs, 6. addresses endangered fish needs that can be met by existing hatchery. facilities as well as the need for additional hatchery facilities including facilities in different parts of the upper basin, 7. provides recommendations for expansion or modification of existing facilities or new construction, with estimates of costs for construction and operation of these facilities, and 8. provides specific recommendations for consideration and action by the Program participants on the propagation of endangered Colorado River fishes as a recovery element. This plan is intended to serve as a reference document or guide for the propagation of the four endangered Colorado River fishes. IV. BACKGROUND The Colorado River and its tributaries flows through 2,317 km (1,440 miles) of arid land and serves over 15 million people with water for municipal use, irrigated agriculture, industry, and mining. Water development in the Upper Colorado River Basin to serve these multiple uses has altered the natural river system. This development has resulted in changes in the historic water regime of this important river system that, in turn, has affected water temperatures and habitat such as backwaters and flooded bottomlands that were apparently crucial to successive recruitment of the endangered fishes. Construction of dams in the upper basin also blocked natural migrations of endemic fishes. Subsequently, non-native fishes were introduced, either intentionally or accidentally, that have become established in the river and are suspected to be competitors with, or predators on, the native fishes in this unique river system. These changes have resulted in the four endemic large river fishes (Colorado squawfish, bonytail, humpback chub, and razorback sucker) being listed as "endangered" under the Endangered Species Act of 1973, as amended.. These endemic fishes played a positive and important role in the lives of Upper Colorado River Basin residents (Quartarone 1993). Although spawning has been documented and larvae and juveniles of some of the endangered fishes have been collected in the upper basin, the primary limiting factor is the lack of recruitment to maintain self-sustaining wild stocks. Survival of young fish appears to be affected most by predation and competition by non-native fishes and loss of nursery habitat that provides sufficient food of the right size at the right time (e.g., match-mismatch principle). The four endangered Colorado River fishes are known to be long-lived (Henrickson and Brothers 1993; Miller et al. 1982; McCarthy and Minckley 1987). The Colorado squawfish, bonytail, and roundtail chub (Gila robusta) were reported to produce strong year classes that were correlated with streamflows (Vanicek and Kramer 1969). McCarthy and Minckley (1987) concluded that 24 to 44 year-old razorback suckers in Lake Mohave were hatched prior to or coincidental with construction and filling of the reservoir and that some year-classes were stronger than others. Finally, Kaeding and Zimmerman (1983) provided evidence of differences in numbers of humpback chub juveniles between years. High flows in the Little Colorado river during 1993 was accompanied by 10