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<br />UO.158 <br /> <br />is at the lop oflheI5-mi!e reach (Fig_ 6) <br />Thus, in lemu Orr<lrage and suitable temper_ <br />ature regime. the IS-mile reach may be <br />located Iocr ncarthc moSI optimal part of <br />the Colorado River for Colorado pikemin- <br />"OW <br /> <br />Low water temperature might also in- <br />hibilsuccessfulspalloTlingbypikeminnowm <br />reachesupSlfeamofPalisadc.lnDeReque <br />Canyon, temperatures necessary for spawn. <br />ing are met, bullheoverall thermal regime <br />may be less than optimal in some years The <br />inilial;ono(spawning in the ColOlado River <br />generally occurs wben river temperatures <br />c,cced 18"CandspawningactivitylaslsJ.g <br />...eeks(TrammellarldChart 1999) Hamman <br />(198]) reponed that females held in race- <br />ways did IIOlspawnuntiltemperaturese,. <br />c.eeded 20'C. In comrolled e~periments. <br />Marsh (19115) found thaI forc!Qls spa....ned <br /> <br />andfcniliudatIS'C,hatchingsuccessand <br />embryo survival was highesl al 20'C, <br />AJlhough some spa\lllT1ing occurs al cooler <br />lemperatures (see BeSlgen el al 1998), <br />maSI spa"ning in lhe Colorado, Green, and <br />Yaml'~ rivers occurs al waler temperalures <br />between 18-22"C (McAda and Kaeding <br />199], Tyus ]990, Bestgen et al 1998, <br />Anderson 1999, Trammel and Chart 1999) <br />Analyses of tempera lure records at Cameo <br />(1986-1996)indicalelhaI18"C ise~ceeded <br />in bolh wel and dry years, bul inwel)'ears. <br />20'C maybe only brielly attained IFig 7) <br />Thus, in some years su;lableoonditinns for <br />spawning may be ofshon duralion [n <br />addilion. the delayed annual warming of <br />upstream reaches will likely delay the onWI <br />ofspa\lllT1l11J1., resulting m larvae havinll a <br />shorter first.yeargrowing se8son than if <br />produced in moredo\lllT1slream reaches, <br /> <br /> 25 <br />- <br />u <br />0 <br />$ 20 -~----, <br />$ SP"'W~I'-'G <br />~ -------- <br />~ <br />~ <br />- <br />$ 15 <br />~ <br />0 <br />- 1993 <br />m <br />~ <br />Ii 10 <br />E <br />$ <br />.... <br /> 5 <br /> MAY JUN JUl AUG SEP OCT <br /> Month <br /> <br /> <br />Figure 7. Main channelll.'1Tlperatures (May-OClobcr) allwo ~ites ill t~c Colorado River during <br />a wet year, 1993, Measurements are from USGS gauging Slal10ns al. Cameo and the <br />C'olorado_Utah Slale line Ploued daily \alues are Ihe avera8e oflhe dally ma~imum and <br />mimmum readings Timingand duration oflemperalures in e~eess of I S" and 20. C (see le"t) <br />at lhetwosilesare shown foroornparison <br /> <br />" <br />