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<br />velocity wat~r current microhabitats such. as areas .behind, boulders, .,eddychannels, and eddy
<br />.fences (the zone of water between eddy andmainchannel) (Valdez and Nilson 1982). ' ~.l
<br />
<br />In"U1,e Grand Canyon; habitat use by the humpback chull..nas been reported ,by' Kaeding and
<br />Zimmerman (1983), Maddux et al. (1987), and the preseilCGCES Phase II work by AGFD and
<br />. .. ..,~Q/WESr..l",Qver,;8l1%.iio~1h.e eAultMumpbaek::clwb.:.captured..:or..:contactedcby.;ndio-tracking
<br />we,;e found by. Va,ldezandHugentobler-.( 1993),,10 beJromteddycomplexes :(activereeirculating
<br />eddies and eddy return channels). Surface mapping (flows, from about 4,000 to 16,000 cfs) .
<br />.' showed the availability ,ofthosesame.habitatswas;20% .for.eddies,:less'.tharr 1%. for return
<br />channels, and. 56%',fo! runs (Valdez,et aLI992a);",',Boulders,and'sandwerethe dominant
<br />substrate, . water. velocities wereJoW,.,and: depths 'ranged from 1.2 to 12 m (n= 11).
<br />
<br />PrelimiRary iQformatio.n 'from theon-going studies.in .the Grand Canyon and from studies
<br />conducted in the upper basin (Valdez and Nilson 1982;' Kaedinget -al.1990) found humpback
<br />chub to have an affinity for specific locations. . In,the Grand Canyon; movement of 48 humpback
<br />chub over a period of 5 to 149 days was an average of 1.3 kilometers from release site to last
<br />contact site. Movements of humpback chub in response to daily changes in' flow (ramping) may
<br />be due to feeding behavior or to changes in habitat (Valdez e.t al. 1992a).
<br />
<br />Migratory movements such as those observed for the Colorado squawfish have not been reported
<br />for the humpback chub. In the Black Rocks radio-tracking study, adult humpback chub rarely
<br />moved from the area suggesting that habitat requirements, including.spawning, are met in that,
<br />area (Archer etal. 1985). The longest movement recorded for the humpback chub in the Grand
<br />Canyon was an individual PIT and radio-tagged near the LCR and captured 261 days later about
<br />98 kilometers downstream (Valdez et al. 1992a).
<br />
<br />Humpback chub feed on aquatic and terrestrial invertebrates throughout the water 'co1umn
<br />including the bottom of eddies or other such areas where food organisms may collect (Minckley .
<br />1991). Mormon crickets (Anabrus simplex) were a significant food item in one upper basin
<br />study (Tyus and Minckley 1988). Kaeding and Zimmerman (1983) sampled stomachs of
<br />humpback chub from the LCR (n=26 with 12 empty) and Colorado River.fli=18 with 5 empty)
<br />and found immatureChironomidae and Simuliidae larvae dominant. They noted that the
<br />amphipod Gammarus was uncommon in stomachs although abundant in the mainstem. Two
<br />stomachs from the LCR contained fish, including a fathead minnow (Pimephales promelas).
<br />Mainstem collections had a larger number of organisms than those from the LCR. Valdez et
<br />al. (l992a) evacuated eight stomachs (non-lethal'pumping) from mainstem humpback chub and
<br />found primarily aquatic invertebrates; the dominant species was Gammarus ..with the algae
<br />Cladophora glomeraraalso represented.. In 1992; stomachs_of 43 humpback, 'Chub were sampled
<br />in. themainstem, andSimulids were..62.% oLallfood.,items;,' amphipodS: were 24%, and '
<br />chironomids were B%', (Valdez and Hugentobler 1993).
<br />
<br />Spawning
<br />
<br />Environm.entalvariables.importanLto.. the reproductive .process of,.the humpback. chub are '
<br />believed.to he'hydrology, water temperature,andl'hotoperiod, but'endogenousfactors such as
<br />stage of maturityand.genetic lineage appear influential: but,.undefined,(Tyusand.Karp 1989).'
<br />
<br />15 December 1994 final biological opinion 2-21.93.F.167
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