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<br />io <br /> <br />... <br />. <br /> <br />INTRODUCTION <br /> <br />The Colorado River and its tributaries have been significantly <br /> <br />alt"red by man (Joseph et al., 1977; Carlson and Carlson, 1982). <br /> <br />Presumably because of this circumstance, there have been changes <br /> <br />within populations of the native chub (genus ~) species <br /> <br />complex. <br /> <br />The situation for chubs in the Upper Colorado River is <br /> <br />well documented in Tyus et al. (1982) and summarized below. <br /> <br />Bony tail chubs (~.elegans) used to be very abundant (Jordan and <br /> <br />Evermann, <br /> <br />1896) but now appear to be <br /> <br />almost extinct. <br />. ~';-rn <br /> <br />HumpJack <br /> <br />chubs (G. cypha) have also undergone a substantial decline in <br /> <br />numbers. Roundtail chubs (Q.. robusta), on the oth.:>rh?nd, appe3r <br /> <br />common in certain areas. Supposed morphological intermedia~es or <br /> <br />intergrades also occur (rHnckley, 1973; Tyus et al., 1982), their <br /> <br />existence thought to be due to interspecific hybridization (Minc- <br /> <br />kley, 1973). <br /> <br />The dynamics and interrelationships of chub populations are <br /> <br />confusing due to our ignorance of the species complex. <br /> <br />Horpho- <br /> <br />logical discriminations among chubs are based on insufficient <br /> <br />criteria (Valdez and Clemmer, 1982), the result of these fishes <br /> <br />never receiving adequate systematic examination (Miller, 1946, <br /> <br />1 961 ) . <br /> <br />Consequently, chubs are often not confidently identified <br /> <br />to species. <br /> <br />Because of th3 taxonomic uncertainties among the Colorado River <br /> <br />2 <br />