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if efforts are undertaken to disrupt spawning and reduce survival of early life stages of <br />smallmouth bass. <br />Fast growth of smallmouth bass observed in the Yampa River in 2005 suggests that <br />smallmouth bass may be even more problematic than previously thought. This is because our <br />unpublished simulations showed that age-0 smallmouth bass should grow fast enough in most <br />years to grow to a size large enough to capture and consume most age-0 native fishes in the same <br />summer. This should be true even if native fish hatched substantially earlier than smallmouth <br />bass. Higher flows in non-drought periods and accompanying cooler water temperatures may <br />partially ameliorate this situation by slowing growth of age-0 bass. It also seems clear that <br />smallmouth bass abundance needs to be reduced to in order to increase survival rate of native <br />fishes. It is not clear if a return to more normal hydrologic conditions will restore native fishes <br />now that smallmouth bass are so well established. <br />Yampa River fishes, hypotheses regarding native fish response.-There are several <br />hypotheses that may explain why native fishes have not responded to predator removal (J. A. <br />Hawkins, annual reports) in the study area. The first and most obvious explanation is that an <br />insufficient number of predator fish may have been removed. Evidence from Anderson (2002) <br />and our own isolated pool data suggest that in the recent past and now, that native fishes are able <br />to survive in the Yampa River in certain situations. Those situations have a common factor, low <br />or no smallmouth bass present. Even though present removal efforts are intensive and <br />reasonably successful, many smallmouth bass still remain in the study area. It may be that <br />removal efforts need to be increased both within the study area, and outside of it, to prevent <br />immigration. It may also be that age-0 smallmouth bass reductions in the treatment reach <br />happen too late in the year to benefit native fishes. However, first sampling to remove age-0 <br />smallmouth bass occurs just after smallmouth bass swim-up. Further reductions in age-0 <br />smallmouth bass abundance may also be realized if hydrologic conditions return to a non- <br />drought state. Higher and cooler flows will likely reduce the suitability of the Yampa River for <br />smallmouth bass and may act as a riverwide mechanism to reduce bass abundance. <br />19 <br />