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Spawning Thirty-nine humpback chub (16 males, 5 females, and 18 fish that were tuberculate but not ripe) were captured in breeding condition. These fish were captured in shoreline eddy habitats in a 48-km reach (km 20.8-68.8) in Yampa Canyon and in a 2-km reach (km 545.6-547.2) in Whirlpool Canyon (Figure 1). River turbidity precluded observation of actual spawning behavior and spawning microhabitat. All ripe fish were silvery colored with "golden aspects" on the dorsal portion of the body. Ripe males always had some orange coloration on the sides of the skull, opercles, abdomen, and paired and anal fin bases. Both ripe males and ripe females usually bore a light tuberculation on portions of the head, nuchal hump, opercles and paired fins, and was more robust in males. Ripe fish ranged from 232 to 382 mm TL; males averaged 311 mm TL (N=16, range 232-370 mm) and 229 g (N=14, range 130-348 g) and females averaged 300 mm TL (N=5, range 280-333 mm) and 230 g (N=4, range 160-336 g). Tuberculate fish that were not ripe averaged 303 mm TL (N=18, range 232-382 mm) and 203 g (N=17, range 92-356 g). From mid-May to late June, 1987 to 1989, ripe humpback chub were collected following highest spring discharge (Table 1; Figure 2, spawning period delineated by first and last capture of ripe fish). Captures of tuberculate but unripe fish also occurred within this 5-6 week period of gradually decreasing river flows (Table 1). Although sampling in 1986 did not include pre-runoff conditions and thus, was excluded from Figure 2, four humpback chub in breeding condition (2 females, 2 males) were collected in July. Ripe fish were captured in water temperatures of about 19.50C (range: 14.5 to 230C). 9