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, L <br />adequate to evaluate the reproductive success of humpback chub. Their <br />restriction to specific river reaches may require more intensive investigation <br />of the areas where they are most common--Black Rocks, Westwater Canyon, and <br />Cataract Canyon. It is also likely that spring runoff is important in <br />maintaining these unique habitats. Valdez and Clemmer (1982) suggested that <br />runoff may contribute to reproductive isolation between humpback and roundtail <br />chubs; however, Kaeding et al. (1990) felt that other isolating mechanisms may <br />be more important. Further investigation into isolating mechanisms may be <br />necessary. <br />Bonytail <br />Bonytail are so rare that it is impossible to estimate the effect <br />reduced spring runoff may have had on this species. However, like the other <br />native species of the Colorado River Basin, bonytail are accustomed to <br />regular, high-runoff levels and the reduced frequency of these events was <br />probably detrimental to the species. Reduced spring runoff could affect any <br />reintroduction program attempted for the species. <br />SUMMARY <br />Water Temperature <br />Water temperature is essentially unchanged in the Colorado River, but <br />reduced somewhat in the Gunnison River within the historic range of razorback <br />sucker and Colorado squawfish. The reduced temperature could affect spawning <br />success of either of the two fishes if remnant populations still exist there. <br />The success of future reintroductions of either species might be improved by <br />relatively minor temperature increases in the Gunnison River. <br />29 <br />