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EXECUTIVE SUMMARY Current Status: The razorback sucker, Xyrauchen texanus (Abbott), was listed as endangered 01\ 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 distnbuted. 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 L1mltlno 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 is a primary reason for the virtual failure of recruitment in razorback sucker populations. Recovery O~ectlves: Protection and expansion of three existing populations, and establishment of four 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, down list 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, and the Green and Yampa rivers has been reversed and target population sizes are maintained or exceeded for at least 10 years. The long-term goal is to sufficiently recover the fish to allow downlisting and then delisting. Downlisting to a threatened status would signify that immediate extinction in the wild has been averted, and will be possible when one additional population has been established in the upper basin and one additional population has been established in the lower basin. Delisting will be possible after the fish has been down listed to threatened, and two additional populations of the fish have been established and protected in either the upper or the lower basin. Actions Needed: (1) Reverse the decline, increase, and stabilize three existing populations by management actions: Lake Mohave, middle Green River and Yampa River, and lower Green River. (2) Protect habitats of these populations from further degradation. (3) Restore habitats to make them compatible with recovery goals. (4) Maintain existing genomes in hatchery refugia and increase diversity as necessary. (5) Augment or reestablish populations of the fish in its critical habitat. vi I