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20 past 20 mm in size. The lack of recruitment places this species in a precarious situation. Because of its recent listing, there is no formal recovery goal for the razorback sucker. However, the immediate goal is to prevent their extinction in the wild. Adults ~, In the Upper Colorado River Basin, adult razorback suckers were captured predominantly from the upper Green River (Mile 176-345) and in the lower 13 miles of the Yampa River (Azevedo 1962; Vanicek et al. 1970; Holden and Stalnaker 1975; Seethaler et al. 1979; McAda and Wydoski 1980; Miller et al. 1982a; Tyus et al. 1982b; Tyus 1981; Tyus and Karp 1990). Catch-effort estimates suggest that adult razorback suckers are rarer than other native suckers and the endangered Colorado squawfish. Radio-tagged razorback suckers overwintered in the Jensen, Island Park, and Echo Park reaches of Green River (McAda and Wydoski 1980; Valdez and Masslich 1989). In winter, razorback suckers used slow runs, slackwaters, eddies, and backwaters in the Green River, where local movements increased with flow fluctuation (Valdez and Masslich 1989). Razorback suckers in breeding condition were captured primarily on several cobble/gravel/sand bars in the lower Yampa and upper Green Rivers (including Echo Park and the reach from Ashley Creek to near the lower boundary of. Dinosaur) but also were collected in flooded shorelines, bottomlands, and tributary mouths (including Old Charley Wash, lower Ashley Creek and Ouchesne River, and Stewart Lake Orain (Tyus and Karp 1990)). From 1987 to 1989 (low and moderate water years), most ripe fish (98 percent) were collected in riffle areas, but during the high water of 1986, 30 percent of all ripe or tuberculate razorback suckers were captured in flooded river bottoms of Old Charley Wash and Stewart Lake Drain. Twelve ripe adults were observed in Old Charley Wash in late May-early June 1986 at flows of about 19,000-20,000 cfs (Tyus and Karp 1990). Minration Razorback suckers exhibited both local and long-distance spring and summer movements (Tyus 1987; Tyus and Karp 1990). Two spawning migrations-were detected with fish movement between lower Yampa and upper Green Rivers and movement between upper Green River and Ouray area (Old Charley Wash and lower Duchesne River (Tyus and Karp 1990)). Soawnina Spawning of razorback suckers occurred during ascending and highest spring peak flows, as indicated by capture of ripe fish (Tyus and Karp 1989 and 1990). Ripe fish were captured in main channel habitats at water temperatures of about 14-15 °C (Tyus 1987; Tyus and Karp 1990). However, temperatures averaged 19.6 °C (range 17.5-21 °C) in flooded areas (Old Charley Wash and Stewart Lake Drain) in spring 1986 when ripe razorback suckers were present. Main channel temperatures were colder (mean 15.6 °C, range 15-16.5 °C) at this time, which suggests that razorback suckers may seek warmer habitats in the