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Wyoming <br />N <br /> Yampa <br /> ~i <br /> Q- White <br />0 100 200 <br /> c q <br /> <br />Kilometers °~ <br />~ Colorado <br /> ~ <br />Utah <br /> Gunnison <br />Nevada <br />t <br />e <br />Q;\~ <br />Co% <br />raao <br /> San Juan <br />B <br /> New Mexico <br />Arizona <br />California <br />C <br />Gila River <br /> Mexico <br />FIGURE 1. Map of the Colorado River basin showing rivers that <br />historically provided habitat for Colorado sgauwfish (light <br />lines) and those that presently contain Colorado squawfish <br />(heavy lines). (Modified from Seethaler 1978.) Sites of <br />telti~erature-data collection in upper (A), middle (B) and lower <br />(C) river reaches are indicated. <br />for other species. Behnke and Benson (1983) speculated slow growth <br />of Colorado squawfish in the upper basin resulted from limited food <br />availability, but this seemed an unlikely explanation because prey <br />species are abundant (cf. Tyus et al. 1982). A plausable <br />explanation for slow growth remained elusive until the study of <br />Osmundson (1986). He stocked five-month-old Colorado squawfish 50- <br />75 mm long into a pond that had abundant age-0 common carp <br />(Cvprinus carpio). One year later these squawfish averaged 231 mm <br />TL and the largest was 304 mm long (Figure 2), clearly indicating <br />potential growth is much greater than that shown by squawfish in <br />upper basin rivers. Moreover, because the pond warmed earlier in <br />the season and thus had a longer growing season than did the <br />-109- <br />