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<br />CJ25=-4 <br /> <br />of best professional judgment. Participants were therefore asked to describe scenarios <br />that could be used for applying a specific control technique for the control of one or <br />more nonnative species at particular geographic locations. <br /> <br />Solutions <br /> <br />Scenarios for control of nonnative fishes involve four significant dimensions: <br />(1) geographic scope, (2) nonnative species, (3) source of the non natives, and <br />(4) control techniques. The geographic considerations are arguably the most important <br />of the four dimensions for defining a scenario. For example, a scenario could target <br />critical habitat of one or more listed species, or it could specify the most important <br />sources of the nonnatives. The selection of a target nonnative species is an important <br />consideration that will shape a control scenario. Once the target location and <br />nonnative species have been selected, the control technique can be tailored to the <br />target species and the principle source of the nonnatives. <br /> <br />An abbreviated version of the many scenarios presented at the workshop is <br />shown in Table 10. The scenarios generally follow three basic themes. The first theme <br />involves preventing nonnative fishes from entering the system. For example, <br />escapement controls could be installed on major reservoirs like Starvation, Elkhead, <br />Kenney, and Highline. For ponds in the floodplain, chemical techniques can be applied <br />to eliminate nonnatives. In general, however, stocking policy may be very important <br />especially for floodplain sources. The second theme deals with removal of non natives <br />from the main channel. Typically mechanical techniques such as trapping, would be <br />applied in critical habitat for the removal of larger nonnatives such as channel catfish, <br />carp, and perhaps some centrarchids. Flow management, especially in high gradient <br />areas, has some potential for reducing populations of small cyprinids and the <br />centrarchids, if timed correctly. The third theme involves excluding non natives from <br />interactions with native fish species chiefly during early life history stages. Backwater <br />exclusion devices and the active management of the inundation cycle for backwaters <br />and floodplain ponds could reduce predation on larval nonnative fishes, <br /> <br />The specific geographical area selected for applying control techniques would <br />depend on the theme being pursued and the scope of the control activity. Participants <br />adopted a two-tiered approach in which control strategies were proposed basin wide, or <br />they focused on specific geographic locations. In general, the geographic locations <br />identified in Table 10 conformed with priority areas designated for recovery and for <br />interactions with nonnative fishes (Tables 3 and 4). Important geographical locations <br />included the Lower Yampa and Green rivers (Y1, G1-4) and the upper Colorado River, <br />UC1 and UC2). A few of the strategies were less specific about geographic locations <br />(e.g., "critical habitat", or "nursery areas"), but it was relatively easy to associate the <br />strategies with important habitats described in Tables 3 and 4. Thus, for the most part, <br />participants recommended only a few key geographic areas for implementation of <br /> <br />31 <br />