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, ~, ! ~ , velocity water current microhabitats such as areas behind boulders, eddy channels, and eddy fences (the zone of water between eddy and mainchannel) (Valdez and Nilson 1982). 'I ::. i. ':~ In the Grand Canyon, habitat use by the humpback chub has been reported by Kaeding and Zimmerman (1983), Maddux et al, (1987), and the present GCES Phase II work by Arizona Game and Fish Department and BIG/WEST. By radio-tracking adult humpback chub, Valdez et al. (1992a) found 70% of the contacts were from eddies, 18% from return current channels, and 17% from runs. Surface mapping (flows from about 4,000 to 16,000 cfs) showed the availability of those same habitats was 20% for eddies, less than I % for return channels, and 56% for runs. Boulders and sand were the dominant substrate, water velocities were low, and depths ranged from 1.2 to 12 m (n= 11). Preliminary information from the on-going studies in the Grand Canyon and from studies conducted in the upper basin (Valdez and Nilson 1982, Kaeding et al. 1990) found humpback chub to have an affinity for specific locations. In the Grand Canyon, movement of 48 humpback chub over a period of 5 to 149 days was an average of 1.3 kilometers from release site to last contact site. Movements of humpback chub in response to daily changes in flow (ramping) may be due to feeding behavior or to changes in habitat (Valdez et al. 1992a). t'.'.'.1 . " {, ,;:' t~ ~ , , Migratory movements such as those observed for the Colorado squawfish have not been reported for the humpback chub. In the,Black Rocks radio-tracking study, adult humpback chub rarely . moved from the area suggesting that habitat requirements, including spawning, are met in that area (Archer et al. 1985). The longest movement recorded for the humpback chub in the Grand Canyon was an individual PIT and radio-tagged near the LCR and captured 261 days later about 98 kilometers downstream (Valdez et al. I 992a). Humpback chub feed on aquatic and terrestrial invertebrates throughout the water column including the bottom of eddies or other such areas where food organisms may collect (Minckley 1991). Mormon crickets (Anabrus simplex) were a significant food item in one upper basin study (Tyus and Minckley 1988). Kaeding and Zimmerman (1983) sampled stomachs of humpback chub from the LCR (n =26 with 12 empty) and Colorado River (n = 18 with 5 empty) and found immature Chironomidae and Simuliidae larvae dominant. They noted that the amphipod GammlJrus was uncommon in stomachs although abundant in the mainstem, Two stomachs from the LCR contained fish, including a fathead minnow (Pimephales promelas). Mainstem collections had a larger number of organisms than those from. the LCR. Valdez et al. (1992a) evacuated eight stomachs from mainstem humpback chub and found primarily aquatic invertebrates; the dominant species was GammlJrus with the algae Cladophora glomerara also represented. "1 !.. .~:- (.", ;.>J ., :""1 t.". ::~~' 1<':" "'" ~,,: "'1 .",-. ;f;, ':':1 .."1 Spawnini Environmental variables important to the reproductive process of the humpback chub are believed to be hydrology and water temperature; but other external' stimuli such as photoperiod and internal conditions such as genetic lineage are influential yet undefined (Tyus and Karp 1989). Nesler et al. (1988) found agreement in the literature that temperature and photoperiod 13 October 1993 Draft biological opinion 2,21-93,P-167 10