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deep water, swift currents, and rocky substrates (Service 2002c). Individuals show high fidelity <br /> for canyon reaches and move very little. <br /> Mature humpback chub typically spawn on the descending hydrograph between March and July <br /> in the Upper Basin (Karp and Tyus 1990). Humpback chub are broadcast spawners who may <br /> mature as young as 2 to 3 years old. Eggs incubate for three days before swimming up as larval <br /> fish (Service 2002c). Egg and larvae survival are highest at temperatures close to 19 to 220C <br /> (Service 2002c). Unlike larvae of other Colorado River fishes (e.g., Colorado pikeminnow and <br /> razorback sucker), larval humpback chub show no evidence of long-distance drift(Robinson et <br /> al.1998). <br /> Recruitment appears to be successful in all known Upper Basin populations (Service 2002c). <br /> Survival of humpback chub during the first year of life is low, but increases through the first 2 to <br /> 3 years of life with decreased susceptibility to predation, starvation, and environmental changes. <br /> Survival from larvae to adult life stages was estimated at 0.1 percent(0.001) (Service 2002c). <br /> Survival of adults is high,with estimates approximating 75 percent based on Grand Canyon <br /> adults (Service 2002c). <br /> Growth rates of humpback chub vary by populations,with fish in the Upper Basin growing <br /> slower than those in the Grand Canyon (Service 2002c). Individuals in Cataract Canyon were <br /> 50, 100, 144, 200, 251, and 355 mm total length from 1 to 6 years,respectively(Service 2002c). <br /> Based on sexual maturity and age-to-length ratios, adults are classified as those fish 200 mm or <br /> longer. Maximum life span is estimated to be 30 years in the wild. <br /> Humpback chub move substantially less than other native Colorado River fishes,with studies <br /> consistently showing high fidelity by humpback chub for specific riverine locales occupied by <br /> respective populations. Despite remarkable fidelity for given river regions, individual humpback <br /> chub adults are known to move between populations. Movement by juveniles is not as well <br /> documented as for adults,but is also believed to be limited in distance. For example,no <br /> out-migration by young fish is seen from population centers such as Black Rocks and Westwater <br /> Canyon. <br /> 2.3.3 Population dynamics <br /> Currently, five wild humpback chub populations occur upstream of Glen Canyon Dam and two <br /> downstream. In the Upper Colorado River Basin the two most stable populations are found near <br /> the Colorado/Utah border: one at Westwater Canyon in Utah; and one in an area called Black <br /> Rocks, in Colorado (Upper Colorado River Endangered Fish Recovery Program and San Juan <br /> River Basin Recovery Implementation Program 2010). Smaller numbers in the Upper Basin <br /> were found in the Yampa and Green Rivers in Dinosaur National Monument, Desolation and <br /> Gray Canyons on the Green River in Utah, and Cataract Canyon on the Colorado River in Utah <br /> (Service 2002c). The two populations in the Lower Colorado River Basin occur in the mainstem <br /> Colorado and Little Colorado Rivers. The Little Colorado River population, found in the Grand <br /> Canyon, is the largest known population, harboring up to 10,000 fish (Service 2002c). <br /> 24 <br />