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<br />GG25=-3 <br /> <br />measures. The chief problem with any fish removal measure is one of selectivity. How <br />can the method be applied i,n space or time so that the "by-catch" of natives is <br />minimized? The decision process by which a method is selected must include <br />consideration of any adverse effects the method may have on natives. <br /> <br />Workshop participants ranked control measures according to their potential for <br />controlling nonnatives (Table 9). Some participants expressed great hope in the <br />potential of commercial harvesting to remove channel catfish and perhaps common <br />carp. However, the fear of unintended mortality to some of the native fishes also was <br />of concern. It was thought that choice of bait and placement of traps could make the <br />harvesting technique sufficiently selective to minimize concerns about by-catch. <br />Northern pike and common carp are thought to be relatively susceptible to other <br />mechanical techniques such as nets, electrofishing, or traps. Centrarchids are also <br />susceptible to mechanical techniques but may not be present in sufficient abundance in <br />the main channel to justify the effort. <br /> <br />Management of the flow regime has been suggested as a mechanism for <br />reducing populations of small cyprinids that are reproducing in the main channel as <br />well as centrarchids. There is some concern however that the potential for success <br />with this technique is unproven. <br /> <br />Most mechanical techniques have potential for reducing the abundance of <br />nonnatives in the river. However, if the recruitment of nonnatives cannot be curtailed <br />or eliminated, removal becomes a continuing obligation. The single most important <br />mechanism for reducing recruitment of those nonnatives that do not spawn in the river <br />channel is either to eliminate stocking in the floodplain or to install effective <br />escapement controls on reservoirs and smaller water bodies connected to the river. <br />Populations in the floodplain can be eliminated by chemical techniques, but the risk for <br />loss of natives in the main channel may be too high for chemicals to be applied in some <br />locations. <br /> <br />Ultimately the control measures must reduce the threat of negative interactions to <br />the point where natives will have successful recruitment. To the extent that exclusion <br />structures may enhance recruitment of natives, they would be worth considering. <br />However there are considerable logistical obstacles. <br /> <br />The goal for controlling the nonnative fish populations is to increase recruitment <br />of native fish populations. Control efforts should therefore be focused on various <br />nonnative species that pose the most serious threats and in the locations where control <br />of nonnatives would be the most beneficial. Ideally, each of the promising techniques <br />should be evaluated in scientific trials that would test efficiency and cost effectiveness. <br />Unfortunately, stocks of some native fishes are dwindling and, despite a clear need for <br />more research, the urgency of the situation dictates that actions be taken on the basis <br /> <br />30 <br />