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<br />"roundtail" and "bony tail" chubs. <br /> <br />However, these may have also <br /> <br />been the consequence of size-dependent intraspecific variation. <br /> <br />Those Westwater specimens plotting into the gap tended to be <br /> <br />smaller individuals. <br /> <br />The Colorado River chubs belong to the same <br /> <br />genus; consequently, congeners might resemble each other wh8n <br /> <br />smaller. <br /> <br />Comparisons between fishes caught in 1953 and specimens obtained <br /> <br />in 1985 suggest that a shift in morphology may have occurred <br /> <br />during the interlude between collections. <br /> <br />. "'"il7 <br />Tn8 former sample was <br /> <br />taken before the existence of dams such as Flaming Gorge and Lake <br /> <br />Powell, so the shift may be due to changed or changing environ- <br /> <br />mental conditions. <br /> <br />The above is suggested with great caution, <br /> <br />since comparisons were made between preserved specimens and live <br /> <br />fish. Fixation and preservation can alter morphometry (Parker, <br /> <br />1963; Lockwood and Daly, 1975) and there arc no data to calibrate <br /> <br />such changes for the 1953 Green River sample. <br /> <br />Specimens col- <br /> <br />lected over the years since 1953 <and curated by the University <br /> <br />of Michigan Museum of Zoology' may permit detection of temporal <br /> <br />shifts in morphology. <br /> <br />Additionally, some of the 1953 specimens <br /> <br />may have been small "bony tail" chubs, evaluated superficially on <br /> <br />the basis of a narrow caudal peduncle and the lack of a large <br /> <br />nuchal hump. <br /> <br />Their presence may have somewhat confounded the <br /> <br />analysis; ho~ever, the data may indicate conspecifity for the <br /> <br />"humpback" and "bony tail" chubs. <br /> <br />1 3 <br />