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83 <br />Sigler and Miller (1964) noted the phenomenon in the blue- <br />head sucker populations in Utah and hypothesized a relative- <br />growth rate alteration in young fish developing in fast <br />currents. The caudal peduncle of such fish would simply <br />grow more slowly as the fish matured and comprise a smaller <br />percentage of the standard length at maturity. The narrow <br />peduncle, as suggested by Miller (1946), confers an hydrau- <br />lic efficienc;,- advantage upon fishes in rapid currents. <br />Bolden and Stalnaker (1975) collected bluehead suckers <br />throughout the upper Colorado River drainage and found broad- <br />and narrow-peduncled forms intermixed with intermediate <br />forms at all locations. They noted that broad-peduncled <br />forms predominated in the upper part of the basin, and nar- <br />row forms were more common in the middle Green River sections.. <br />No collection data were presented, but it is assumed that <br />intermixture at a station would indicate presence of both. <br />i <br />extreme forms (CP/SL percentages 4 and 9, respectively) <br />plus a broad range of intermediates. <br />Minckley (1973) also described Folymorphism in this <br />sucker and noted that Colorado River populations showed <br />individuals less pigmented than the morphotypic description, <br />while headwaters populations were more pigmented than the <br />descriptive standard. <br />George Kidd and Clee Sealing of the Colorado Division <br />of Wildlife, having captured and observed thousands of <br />bluehead suckers from the Colorado River near Grand Junction, <br />Colorado, believed that the broad- and narrow-peduncled