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<br />LR <br /> <br />temperatures relative to the river. These factors taken in aggregate suggest that flooded bottom lands are <br />extremely productive areas. <br /> <br />Because of enhanced productivity of food organisms, floodplain wetlands facilitate rapid fish growth and <br />survival within the areas (results of Osmundson) and enhance fish survivorship and growth within the river <br />system. Native young-of-the-year (YaY) fish that leave the river and utilize floodplain wetlands should be <br />a larger size than if they would have remained in the river. Larger native yay fish should be less <br />susceptible to predation by most nonnative fish in the main channel. The increase in size, therefore, should <br />enhance survivorship. These potential benefits could be offset, however, if important nonnative fish <br />species also utilize these hahitats and enhance their growth and survivorship. The potential exists for <br />nonnative fish to he enhanced to a greater degree than native fish because of the lentic nature of floodplain <br />wetlands. Management and maintenance of these wetlands, therefore, will require considerahle <br />information and insights with respect to their use by both native and nonnative species. <br /> <br />The enhanced productivity of floodplain wetlands may also he an important factor in enhancing <br />survivorship of adult native fish. Modde, Tyus and Karp, and Holden and Crist have all documented the <br />use of floodplain wetlands or low velocity areas by adult razorback sucker. Wick (personnel <br />communication) has speculated that these areas may be important post-spawning resting areas. The adult <br />fish may utilize these highly productive areas to replace valuable energy reserves that were used for <br />spawning. Resting habitats, therefore, may be important to enhance the survivorship of the senile <br />population of razorback suckers in the Upper Basin. <br /> <br />To date, most of the effort in understanding the benefits of floodplain function to endangered species <br />within the upper basin has focused on "manipulated" sites that utilize human intervention to control <br />flooding. Little, if any attention, has been given to naturally flooding wetlands in the basin and it appears <br />that a substantial amount of area floods naturally. This scope-of-work adds to previous studies by <br />determining the fish production dynamics ofa range of natural floodplain wetlands and specific application <br />(levee removal) sites as they become available. The application sites will be directly compared to naturally <br />occurring floodplain areas of similar size within specific reaches. <br /> <br />Manipulated sites (i.e., Old Charley, WalterlWalker, etc.) have and will remain important in addressing <br />some specific questions concerning floodplain wetland function. These sites, with their control structures, <br />offer an opportunity to answer questions that would be far to difficult to address in open wetlands. They <br />also alllJW the opportunity to determine the effectiveness of different gears in capturing all life stages of <br />endangered fish (razorback sucker). This information will be critical in future efforts within the Basinwide <br />Monitoring Program as well as the Levee Removal Program. In addition, they also offer an opportunity to <br />use the control structures to increase the effectiveness of fish sampling. A separate scope-of-work will be <br />submitted for experimentation within Old Charley Wash or other manipulated sites. <br /> <br />Emphasis will be placed on the differential utilization of floodplain habitats and the additional food <br />resources available from these habitats between native and nonnative species. Research by Crowl and <br />Lentsch, and that of others, has provided information suggesting that many nonnative species now present <br />in the Colorado River Sysrem are potentially very important as limiting factors to native fish survivorship <br />and recruitment. Channel catfish, northern pike, green sunfISh and smallmouth bass all pose significant <br />threats in terms of their consumptive effects on native species survivorship. Green sunfish, smallmouth <br />bass and northern pike are known to inhabit littoral habitats in Midwestern lakes and reservoirs. Thus, if <br />we are to develop and manage flooded bottom lands to benefit native fish species, we must ascer.ain <br />whether these habitats will also benefit nonnative fishes. First, we must determine whether important <br />nonnative predator species utilize these habitats and whether the increased spatial complexity (and <br />enhanced yay survivorship) provided by aquatic macrophytes will offset losses of native species due to <br />p~dation. Second, if nonnative species do utilize these habitars;we must ascertain whether the additional <br /> <br />3 <br />