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data. Nonetheless, they suggested that there are 100-2,000 humpback chubs in Yampa <br />Canyon, with a best estimate of about 400 individuals. <br />Robust size estimates for the different populations of humpback chub in the upper <br />Colorado River basin are necessary to monitor current management efforts designed to lead to <br />recovery of the species (USFWS 2002). Early efforts indicate that population estimates can <br />be made, but confidence intervals around the estimates are large and determination of <br />significant differences between estimates is difficult. Increased sampling (i.e., four versus <br />three sampling. passes) can improve the reliability of estimates (measured by lower CV and <br />tighter confidence bounds), but may increase unmeasurable negative effects on existing <br />populations. Direct mortality was very low in this study, but the potential for delayed <br />mortality could not be measured. The recapture of two chubs with obvious fungus problems <br />suggests that delayed mortality is possible and should be considered. <br />Initial concern was for direct mortality from the trammel nets which was the major reason <br />for delaying sampling until water temperatures began to cool and for keeping net sets <br />relatively short. The salt bath was also intended to mitigate stress associated with handling. <br />However, water temperatures were still relatively warm (mean daily temperature of 18-20 °C <br />in late August to mid September) and injuries to the skin associated with net wounds or other <br />aspects of handling could lead to fungal infections that the fish might not be able to overcome. <br />Water temperature is an important factor in a fish's ability to deal with fungus that might be <br />associated with skin injuries. Sampling could be pushed farther back into the fall when water <br />temperatures are cooler. However, completing three or four sampling passes with intervening <br />rest periods means that sampling could only be delayed by a few weeks at most; mean-daily <br />temperatures are still 15-19 °C in mid to late September. Mean-daily temperatures decline to <br />~10 °C by mid October which might result in a reduced catch rate because fish move less at <br />the lower temperatures. <br />Alternate sampling methods could also be used. Trammel nets are generally considered to <br />be most effective for capturing humpback chubs (personal observation; Chart and Lentsch <br />19996), but electrofishing and angling can also effectively capture humpback chubs (e.g., <br />Karp and Tyus 1990, Haines and Modde 2002). However, catch rates for those two <br />14 <br />