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20 <br />River in 1963 when maximum daily water temperatures were 12.6° to 17° C <br />(Archer et al. 1985). In Grand Canyon humpback chub spawn in the <br />spring between March and May in the Little Colorado Ri~rer when water <br />temperatures are between 16° and 22° C. Swimming abilities of young- <br />of-year humpback chub were determined to be significantly reduced when <br />laboratory water temperatures were reduced from 20° to 14° C. Many <br />young-of-year humpback chub are displaced from the Little Colorado <br />River into the mainstem by monsoonal floods from July through <br />September (Valdez and Ryel 1995). Young humpback chub are found in <br />low velocity shorelines and backwaters. Survival rates are extremely <br />low and believed to be less than 1 in 1,000 to 2 years of age. Low <br />water temperatures and predation are believed to be that primary <br />factors. Valdez and Ryel (1995) estimate that 250,000 young humpback <br />chub are consumed by brown trout, rainbow trout, and channel catfish. <br />Backwaters, eddies, and runs have been reported as common capture <br />locations for young-of-year humpback chub (Valdez and Clemmer 1982). <br />These data indicate that in Black Rocks and Westwater Canyon, young <br />utilize shallow areas. Habitat suitability index curves developed by <br />Valdez et al. (1990) indicate young-of-year prefer average depths of <br />2.1 feet with a maximum of 5.1 feet. Average .velocities were reported <br />at 0.2 feet per second. <br />Ps1F]~yation D~+namics <br />Population estimates for the Blackrocks area is 3,500 aidulte and for <br />Westwater Canyon the adult population is also estimated to be 3,500. <br />Anal dais of Sn .i c( riti al Hahitat 1ik 1y to be Aff ec,r„~A <br /> <br />Valdez et al. (1982b) and Wick et al. (1979, 1981) found adult <br />humpback chub in Black Rocks and Westwater Canyons in water averaging <br />50 feet in depth with a maximum depth of 92 feet. In these <br />localities, humpback chub were associated with large boulders and <br />steep cliffs. <br />Generally, humpback chub show fidelity for canyon reaches and move <br />very little (Miller et al. 1982 c; Archer et al. 1985; 13urdick and <br />Kaeding 1985; Kaeding et al. 1990). Movements of adult humpback chub <br />in Black Rocks on the Colorado River were essentially restricted to a <br />one mile reach. These results were based on the recapture of Carlin- <br />tagged fish and radiotelemetry studies conducted from :L979 to 1981 <br />(Valdez et al. 1982b) and 1983 to 1985 (Archer et al. :L965; USFWS <br />1986; Kaeding et al. 1990). <br />`J <br />