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_ ._-,.a,u`•t;,,r~ of nat?ve fish species (H~~lden and Stalnaker 1`17~I,;. <br />.. - <br />• scam ]e 'water t~.mperatures in the Colorado--'~iv/ i~rar.d <br />For e. p <br />Canyon below Glen Canyon Dam allow gonadal development of iemaie <br />humpback chubs, but are too cold fc~r successful developmec~t of <br />fertilized eggs (Kaeding and Zimmerman 1983). Water temperatures <br />there were about 10-1~ C during spawning time (Kaeding and Zimmerman <br />1983). Similar temperatures in laboratorys caused nearly complete <br />mortality of humpback chub eggs and fry (Hamman 1982, Marsh 1985). <br />Humpback chub abundance in the Upper Colorado ,Basin may be <br />limited by the availability of suitable habitats (Archer et al <br />1985). Deep water habitats are uncommon in the Upper Colorado River <br />Basin; they comprise only 12e of the 386 km (230 mij between upper <br />Lake ?oweil and DeBeque, CJ (Archer et al.'1985). Dependence on <br />limited habitats makes populations vulnerable to environmental <br />change (Archer et al. I985). Upsfream developments that alter-flow <br />and temperature regimes could adversely affect humpback chub <br />reproduction (Archer et al. 1985) or~create new habitats for <br />competitor and predator fishes that previously could not survive <br />there (Kaeding and Zimmerman 1982). <br />Hybridization between G.i.le resulting from habitat <br />alteration is considered a threat t~ the genetic integrity of <br />humpback chubs (USFWS 1979). Such hybridization is physically <br />Possible (Hamman 1981, Archer et al. 1985}. The existence of <br />"intermediate" Ci.l~~ firms may be evidencr_ of hybridization <br />(holden and Stalnaker 1970). Ilowevcr, few specimens appear <br />"intermed.iatc.", inciicatin~; that reproductive isolation mechanisms <br />10 <br />