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<br />Olh17.i5 <br /> <br />tively large populations occupying quality <br />habitat) are believed critical for persistence <br />ofmetapoPI..!ations(SchoenerIQQ1,Harri- <br />sonl991,1994,Stanfordetall9(6) In <br />rivers, large alluvial reaches often support <br />corepopulationsoffishes{Lichatowichand <br />Mobrandl995) Thecurrentdistributionof <br />Colorado pikemmnow and the historic <br />distribution of razorback Sllckerin the <br />upper Colorado River appears to fit thi, <br />model, "ith oore populations centered in <br />thealluvialCJfand Valley, <br />To understand the habitat needs of <br />Colorado pikeminnowand rawrback suck- <br />er,anecological persp<.'Ctive IS rcquired that <br />takes imo account all phases of their life <br />cyclesandrecogni7esthatpopulationd)'TIa- <br />micsoccur at a scale enoompas.sing hun. <br />drcds of miles of river Thus, the relative <br />importal}(:eofa particulararca, Sllchasthe <br />15_milereacb, cannot be viewed in isola- <br />tioll,bul must be viewed in the wIltext of <br />howitfl1sintothelargerlifehistorypiclllre <br />A river without good adult habitat cannol <br />support a viable population, just asariver <br />withoul itood spawning or nurSCl)' habitat <br />cannot The reach downwe.am of Moab, <br />lltah is critically important in a similar way, <br />because it contains the best nursery habitat <br />intheC(lloradoRiver. FailuretocoMider <br />these Iacls can lead to the false conclusion <br />that becauloC the 15-mile reach conslitutes <br />only8%oflhe 185 occupied miles of the <br />Colorado River (above the Green Ri"er <br />connuence), it plays only a small role in <br />mainlaining populations of Colorado pike- <br />minnow and razorback sucker Tothewn- <br />lrary, the dala suggest that prime adult <br />habilatisrestrictedtotheupper60milesof <br />this 185-mile-long Colorado River reach, <br />withthebesthabilatandgreatestCOnCenlra- <br /> <br />tionsofaduhslocaled inlhe 33-mile-long <br />Grand Valley. Withthisperspective,lhe <br />importance oflhe IS-mile reach become5 <br />apparent <br />The Re<:overy Implementation Program <br />for Endangered Fish Specie1l in the Upper <br />Colorado River Basin hu plans to provide <br />fish passage at diversion structures up- <br />stream of the 15-mile reach 10 allow Colo- <br />rado pikeminnow and ru.orback sucker <br />access 10 upstream portionsoftheir histori- <br />calrange TheI5_mllereach,ar>dlheshort <br />3_milereachjustupslream,currentlyeonsti- <br />lute the upslream limit of the Colorado <br />pikeminnow's range in Ihe mainstem Colo- <br />rado Ri~r. The Price-Stubb Dam has <br />blockedupslreammovemcnlsoffishessince <br />its con-,lruction in 1911 Razorbacksucker <br />have been found upstre.amofthese diver- <br />sion~ relatively recenlly~ one was caplured <br />in 1991 ncar Rifle, Colorado, some 55 miles <br />up5lrcam of Palisade (Burdick 1992) <br />However, 1\0 similar upstream capture <br />rl:>Cords, either recent or hislonc, e~ist for <br />Colorado pikeminnow despite intensive <br />sampling ITom Price Stubb Dam 10 Rine <br />duringlhe pa5t three decades (Kidd 1977, <br />1979, Valdel. el al 1982~ Anderr.on 1997, <br />Osmundson 199')a) Numbers of pikemin- <br />now in this reach likcl)' diminished over <br />time as a resu1t of the long-lerm elTects of <br />lhedivcrsiondamsprcventingretummigra- <br />tion after larvae or adults moved down- <br />stream Providing passage to lhis area <br />should prove beneficial to the Colorado <br />River population by increasing the amounl <br />of adult habitat Becauseadulthabitatisin <br />short supply, the e~tent 10 which Ihis up- <br />stream reach "ill pro\ide suitable habitat <br />has a beanng on the relativeimponance of <br />the IS-mile reach <br /> <br />8 <br />