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17 It is known that the fish spawn soon after the highest spring flows when water temperatures approach 680 F (Kaeding et a1. 1990: Karp and Tyus 1990a: USFWS 1990b). The collection of ripe and spent fish indicated that spawning occurred in Black Rocks during June 2-15, 1980. at water temperatures of 530 to 610 F: in 1981, spawning occurred May 15-25, at water temperatures of 610-61.70 F (Valdez et al. 1982b). Humpback chub spawned in Black Rocks on the Colorado River in 1983 when maximum daily water temperatures were 550 to 630 (Archer et al. 1985). Backwaters, eddies. and runs have been reported as common capture locations for young-of-year humpback chub (Valdez and Clemmer 1982). These data indicate that in Black Rocks and Westwater Canyon, young utilize shallow areas. Habitat suitability index curves developed by Valdez et al. (1990) indicate young-of-year prefer average depths of 2.1 feet with a maximum of 5.1 feet. Average velocities were reported at 0.2 feet per second. Valdez et al. (1982b) and Wick et al. (1979. 1981) found adult humpback chub in Black Rocks and Westwater Canyons in water averaging 50 feet in depth with a maximum depth of 92 feet. In these localities, humpback chub were associated with large boulders and steep cliffs. Generally, humpback chub show fidelity for canyon reaches and move very little (Miller et al. 1982c: Archer et al. 1985: Burdick and Kaeding 1985; Kaeding et al. 1990). Movements of adult humpback chub in Black Rocks on the Colorado River were essentially restricted to a one mile reach. These results were based on the recapture of Carlin-tagged fish and radiotelemetry studies conducted from 1979 to 1981 (Valdez et al. 1982b) and 1983 to 1985 (Archer et al. 1985: USFWS 1986: Kaeding et al. 1990). Critical Habitat Critical habitat has been designated within the humpback chub's historical range in the following sections of the Upper Basin (59 F.R. 13374). Colorado. Moffat County. The Yampa River from the boundary of Dinosaur National Monument in T. 6 N.. R. 99 W., section 27 (6th Principal Meridian) to the confluence with the Green River in T. 7 N., R. 103 W., section 28 (6th Principal Meridian).