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<br />000151 <br /> <br />nooded olf-~hannel habitats whcfe Ihey <br />concentrated during spring (Kidd 1977, <br />Valdezetal 1982) Asrecenllyuthelale <br />I 980s, rawrbad. sucker were still occa- <br />sionally captured in the IS-mile Teach, <br />primarily during their spring spav,lling <br />season(OsmundsonandKaedingl99l) In <br />IhC' 1990s,onJy fourl'iLlorback sucker were <br />captured in the Colorado River and these <br />were found in l~ reach immediately down- <br />stream of the IS-mile reach Adult ((llo- <br />rado pikenllnnow, though rare. are rou- <br />tinely captured in the IS-mile reach <br />throughout the year (Osmund.....n Bnd <br />Kaedin8191l9,OsmundsonetaJ J9'l8).and <br />spawning there has hi.>cn verified by the <br />lXllleClion of lan'ae in 1982 and 1<:195 <br />(MeAda and Kaeding 199], "ndcr~n <br />Ill')9) <br /> <br />SYl'<'THESIS <br /> <br />Di<frihullfm of ";nJ./J/~aetl F;,,'h m (h( <br />Uppa C%m"" Rn't'f <br /> <br />Thuugh more is known about the life <br />history of Colorado pikeminnow lhan of <br />razotback sucket, both specil'S evidenlly <br />tl'<luirelargem~'1chesofriverlofulfilllh~'lr <br />respective life history needs Asindividuals <br />progress through .arious life stages. their <br />hahitatrl'<jlliremenlschange Forinstancc, <br />young Colorado pikeminnow rear in reach. <br />cs\\oherenurseryhabital ismosl suilable, <br />whereas larger and olderindi.-iduals move <br />tomoreupstreamhabitatswhefCfllodfor <br />aduhs is more abundant (Osmundson et al <br />1998) ThisdiSlributionrancmappcarsto <br />bcconsistem in both Colorado and Green <br />river systems Coloradopikeminnoware <br />the top prcdat(lrin theriveriTle food chain <br /> <br />They subsist almostexcll.lsivelyonadietof <br />fishes and prefer areas where prey lhh are <br />abundant In the Colorado River,thegtCllt_ <br />est fish production and consequently the <br />grealestnumbcrofadultColllradopikcmin_ <br />now occur upstream of Westwater Canyon <br />During recent studies (O.mundson 1999a), <br />e1ectrofi,'1hingcatch ratesofforage-size fish <br />(moslly native suckers) were 3-4 times <br />higher in reaches upstreamofWeslwaler <br />Canyon lhan in reaches d()Wflstre.am (see <br />Fig 2) InlheGreenRiver,themajorilyof <br />adult Colorad() pikeminnow are also found <br />in upper reaches as well as in two major <br />tributaries. the YlImpa and White rivers <br />(/-.-lcAda et al 1994) <br />Upstream reaches generally havegre3t. <br />ernumbers of forage fish becausc food for <br />these fishes {algae and aquatic insects) IS <br />more abundant than in downslream reaches <br />(Lamarra 1999) lligherwaterclarily,and <br />lhercl"nrede..perlightpcnClralion.allo..... <br />greater production of phytoplankton (free- <br />floating algae) IInd pcriphyton (algae that <br />grows on rock surfaces) ThC5e algae ale <br />food f(lf various sPCclcs of aquatic IIlvertc. <br />bralcs Also,uppcrri.erreachesgenerally <br />have Slttpel gradientslhan the more d,)wn. <br />sneamlcachcs, causing water to flow more <br />sv.lflly o\'er lhe subslrate Thi~ serve~ 10 <br />clean silt and sand from theuppt'T layer of <br />gravelandcohble Silt.freecrcvicesaround <br />rocksprovideimponalllal1l1chrnent~itesand <br />living spaces for aquatic invencbratel <br />(Osmund.sonandSchcer 1998) Algacand <br />aqualicinvencbrateslivingintheseciean <br />substrates are fooo for nativ'c fishes such as <br />bluehcad sucker (('/O,'I/om".>- dl'n",,,t,,.>-, <br />llannc1mouth sucker ('a"'.>/o",I<11<IIII'IIIIII_'- <br />and roundtail chub Gi/t,mf""w which are <br />potential prey for Colorado pihminno....... <br /> <br />3 <br />