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<br />U0i1756 <br /> <br />Eleetwfishing surveys between the <br />Priee Stubb D~m and Rille, Colorado dem- <br />onstratethatanatJundaneeofnativesuckcrs <br />and chubs live in this reach and could serve <br />as forage for adult Colorado pikeminnow <br />(Wydoski 1994,Anderson 1997,Osmund- <br />son 19<Na). Uowever,becauseofprogres_ <br />sivcJy cooler water tempe'TItures. the mar. <br />gin ofthl" historic range for these warm. <br />waler species occurs somewhere within <br />these upstream reaches. UpslreamofPaJi- <br />sade, a transition l.onebegins~tween a <br />downstream warm.waler fish community, <br />historically domInated by chubs, n~hve <br />suckers,andCotoradopikeminno"",andan <br />upstream coltl.water fhh community. dumi. <br />naledbysalmonidspeciessuchastroutand <br />mountain whilefish Ilowtheendan~ered <br />fish uliliu this reach oncc access is again <br />provided remains to be secn. Inlheintcrim, <br />predicting habitat suilahitity forlhcse fish <br />requires an ewluatlon of the thermat re- <br />quirementsofthe species Bnd the thcrmal <br />regime of the reach <br /> <br />H..t<ll;mr._hll' 8"""':../1 h'ml',:mlUre "',.} <br />""..Jr!)Ufrlf>ulw/I <br /> <br />Positioningofaduhs, both localtl' and <br />along the length of the river, is likely driven <br />by growth maximitlltion (f1ughes t998), <br />and grov,1h is largcly dependent on the <br />interaction of food availability and water <br />temperamre(Weathcrley1972) Achieving <br />ma~imum grnwth potential enhances the <br />atJility of the individual to survive and n". <br />produeesuccessfiJlIy In many fish species. <br />large females produce more and larger eggs. <br />thcrebyenhancingtarvalsurvival(Monte1e. <br />one and Houde 1990; Brandt and Kirsch <br />I99J) Although temperatules in the <br /> <br />Palisade.to--RiOe reach are only a few de- <br />grees centigrade (C) lower than in the <br />Grand Valley on any given dllY, this differ. <br />encecan result in a significant reduction in <br />thermal units needed for fish growth over <br />thccouf$Cofayear <br />Controlled.laboratoryexpcnmcmtshave <br />shown thai growth rate of yearling Colo- <br />rado pikeminnowi! maximized at lS'C. ,\t <br />20'C, growth rate is 54% oflhe mUJmum; <br />al 15'C, gro"1h is only 180/0 (B1ack and <br />Bulkley 19115a), at IJ'C, Colorado pike. <br />minnow cease 10 grow (Kaeding and Os. <br />mundson t9SS) Otherlabstudiesdcmon. <br />straled that 2S'C is the prefcrred tempera- <br />mreofyellrling and subaduttpikeminnow <br />(Black and Bullodey 198~b) and preftrred <br />temperature generally corresponds 10 lhe <br />oplimum temperature for many physiotogi- <br />calproccssesindudinggrowth(eg Mag- <br />nusoncl al 1979) ToreveaJ the effect of <br />low temperature on habitat SUitability, <br />annual,accumulatedlhermalunitsa".ilabte <br />for growth can bec.alculated for various <br />rcachesofriwr, For comparative purpoSt's, <br />Kaeding and Osmundson(IQII8) developed <br />an index wherd>y mean daity tcmperalures <br />areconn.'1tedt(\valuesrelahvetothemaxi. <br />mum potemia] (1 0) for grov,1h al thcopti. <br />mum tcmperature (250 C) These thermal <br />units can then be l\IJmmed to provide an <br />annual value for a specific location <br />Usingmulti-yeardala from a series of <br />tllermographs located at various sites along <br />theri\'Cf(seeFig 1). Osmundson (Ima) <br />conwr1ed daily temperatures to thermal <br />units fOf Cotorado Plkeminnow gro"1h <br />Average annual thermal units (ATU) at <br />Palisade were 79~~ of tht: average at the <br />ColoradolUtah state line (about 48 milCll <br />downstream) At Cameo, the aVl'fage was <br /> <br />9 <br />