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Spawns under decreasing flow regimen with increasing temperatures in summer. In the Green River, Wyoming, spawns July-August, apparently when water temperature is at least 20-22 C. In the lower Yampa River, western Colorado, apparently spawned as early as mid-June or as late as August in different years. Eggs hatch in 3.5-6 days at 20-22 C. Survival and hatching best at 20 C. Larvae enter stream drift and are transported downstream for about 6 days, traveling an average distance of 160 km to reach low gradient nursery areas. Sexually mature in 5-7 years (at 50 cm TL in the Green River). May live 30 years or more . Makes extensive spawning migrations; spawning migration of up to 205 km (one-way) has been documented; in late spring, different individuals migrate upstream from Green River and downstream in Yampa River to common spawning area. |
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Restricted to large rivers of the Colorado River basin, formerly in the mainstream Colorado River and major tributaries (Gunnison, White, Yampa, Dolores, San Juan, Uncompahgre, Animas, and Green rivers), from Mexico and Arizona to Wyoming. Present distribution drastically reduced from original. By the mid-1980s occurred only in Upper Colorado River basin of Colorado, Utah, New Mexico, and Wyoming; mainly in the Green River in Utah and in the Yampa and Colorado rivers in Colorado and portions of Utah; not seen below Glen Canyon Dam since 1968. Adults predominate in the White and Yampa rivers, young in the Green River.
Medium to large rivers. Young prefer small, quiet backwaters. Adults use various habitats, including deep turbid strongly flowing water, eddies, runs, flooded bottoms, or backwaters (especially during high flow). Lowlands inundated during spring high flow appear to be important habitats. |
