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The Westwater Canyon anc! Slack Roclts populations exist in <br />short river reaches that possess ~;rc.at depths, p;re:~t water <br />velocities, and substrates of bedrock, boulder, and sand (Miller <br />et al. 1982c). Black Rocks is a narrow, turbulent, deepwater <br />area where the Colorado River passes through an erosion resistant <br />layer of gneiss and schist rock. This 1 mi (1.7 km) reach has -- <br />depths of 19 m (56 ft.) (Archer et tr1. 1985). Shelf areas exist <br />along the edges of deeper water; these provide resting and feeding <br />areas for chubs {Miller et a1. 1982c). <br />Humpback chubs in Black Rocks are found in backwaters, eddies, <br />pools and runs (Valdez et o1. 1982). Adults used areas as deep <br />as 12.2 m (40 ft) in Black Rocks. They can navigate swift water but <br />appear to prefer low-.velocity micro-habitats because most of their <br />time is spent in pockets or eddies (Miller et aI. 19$2c). <br />Adults used shallow water (<5 m or 16.4 ft) during dawn and evening, <br />mid-depth water (5-7 m or 16.4-23 ft) in midmorning and afternoon, <br />and deep water {>7m or 23 ft) at midday and midnight (Valdez and <br />Nilson 1982). <br />Suspected juvenile humpback chubs in Black Rocks and Westwater <br />Canyon were found in low-velocity water, usually over boulder and <br />bedrock substrates (Valdez e.t ~rl. 1Jt32). They usually occupied <br />runs, eddies, or pools, but a few were found along shorelines or in <br />backwaters. Suspected age-0 humpback. chubs in Black Rocks and• <br />Westwater seem to prefer small F~ockets and quiet water adjacent to <br />boulders and swii't water. <br />7 <br />