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EXECUTIVE SUMMARY Curren Status: The razorback sucker, Xyrauchen texanus (Abbott), was listed as endangered on October 23, 1991 (56 FR 54957). A final rule designating critical habitat was published on March 21, 1994 (59 FR 13374). An endemic fish of mainstream rivers in the Colorado River basin, the razorback sucker was once abundant and widely distributed. It now occurs only in remnant populations in a few lakes and river reaches. The largest extant population occurs in Lake Mohave, Arizona, and the largest riverine population occurs in the Green and Yampa rivers, near Vernal, Utah. Habitats and Limiting Factors: Razorback sucker populations have been declining for much of this century. This decline is a result of major alterations to the historical physical and biological environment. Extensive water development projects have depleted flow, altered flow regimes, changed water quality, and fragmented habitat. At the same time, the nature and composition of the fish community has been altered dramatically by the introduction of many nonnative fish species. Predation by nonnative fishes and loss of habitat are primary reasons for the virtual failure of recruitment in razorback sucker populations. Recovery Objectives: Protection and expansion of three existing populations, and establishment of five new ones from remnant stocks or reintroductions. Recovery Criteria: The three steps for recovery of the razorback sucker to a less endangered status are: prevent immediate extinction, downlist to threatened, and delist. The short-term goal, which is to prevent extinction of the razorback sucker, will be considered accomplished when decline of extant stocks in Lake Mohave, the middle Green River and the lower Yampa river has been reversed, those populations are stabilized, and target population sizes are maintained or exceeded for at least 5 years. The long-term goal is to sufficiently recover the fish to allow down listing and then delisting. Down listing to a threatened status would signify that immediate extinction in the wild has been averted, and will be possible when a remnant population has been reestablished in the lower Green River, one additional population has been established in the upper basin, and one additional population has been established either in the upper or lower basin. Delisting will be possible after the fish has been down listed to threatened, and two additional populations have been established and protected. One of these additional populations shall be in the upper and one shall be in the lower basin. Actions Needed: (1) Maintain existing genetic diversity in hatchery refugia and increase diversity if possible. (2) Reverse the decline, increase, and stabilize three existing populations by management actions: Lake Mohave, middle Green River, and lower Yampa River. (3) Protect habitats of these populations from further degradation. (4) Restore habitats to make them compatible with recovery goals. ((5) Augment or reestablish five additional populations of the fish in its critical habitat. vi