Biomanipulation of the largemouth bass Micropterus salmoides population to control invasive species and eutrophication at the Nature Conservancy's Emiquon Preserve

Thompson and Flag lakes were historically known as two of the most productive backwater lakes of the Illinois River. Diminishing natural resources from overharvest and a poor economy encouraged land owners to begin leveeing and draining the Illinois River floodplain in order to pursue agricultural prospects. A long legal battle ensued over ownership of the Thompson and Flag lake area. In the early 1920's, Thompson and Flag lakes were declared private property, leveed from the Illinois River, drained, and farmed.;The Nature Conservancy (TNC) purchased over 2,700 ha of floodplain that included the former Thompson and Flag lakes in 2000 with intentions of restoring the landscape back to what it once was: a fully functional floodplain. Aquatic restoration began in spring 2007 with a large-scale rotenone effort to rid the water in the former Thompson and Flag lake beds that existed in remnant agricultural ditches of nuisance and invasive fish species. Following the rotenone, the area was allowed to naturally flood. A large piscivore population (primarily Largemouth Bass Micropterus salmoides) was established immediately through stocking in an attempt to control two common ecosystem stressors: eutrophication and Common Carp Cyprinus carpio.;I tested the potential of the Largemouth Bass population to control eutrophication and Common Carp over the first two years of restoration of Thompson and Flag lakes (2008--2009) through diet analyses. I also used bioenergetics modeling, a Largemouth Bass population estimate, and observed prey proportions to determine consumptive demand of the population. The Largemouth Bass population foraged optimally in 2008 and 2009. A shift in prey use was observed in July of both years. However, cannibalism, reduced body condition, changes in diet breadth, and high consumptive demand may be suggestive of a density-dependent response by the Largemouth Bass population in 2008, whereas density-dependent responses were not evident in 2009. Increasing water levels at Thompson and Flag lakes reduced consumption of prey fish by the Largemouth Bass population in 2009. Secchi disc transparencies decreased, while Common Carp total catch increased since the beginning of restoration. My results suggest that the Largemouth Bass population may have had greater potential to control eutrophication and Common Carp in 2008 than in 2009. Also, maintenance of water levels and/or piscivore density may be an important factor in biomanipulations of the fish community.;TNC plans to reconnect Thompson and Flag lakes of the Emiquon Preserve to the mainstem Illinois River. I conducted a comparative diet study on Largemouth Bass inhabiting backwater lakes with varying levels of connectivity to the Illinois River (contiguous, seasonally isolated, isolated) and bioenergetics modeling to predict the response of the Largemouth Bass population at Thompson and Flag lakes to various reconnectivity scenarios. Prey use by Largemouth Bass in seasonally isolated lakes was similar to that of contiguous and isolated lakes, but different in contiguous and isolated lakes. Largemouth Bass consumed more prey fish biomass in seasonally isolated lakes than other habitats; however prey fish diversity was greater in their diets. My results suggest that potential eutrophication and Common Carp control may be greater in seasonally isolated management scenarios and water level and/or piscivore density management may be important when attempting to minimize these two ecosystem stressors. The Emiquon Preserve has a vast historical heritage and has been important to the ecology of the Illinois River and its floodplain for millennia. The Emiquon Preserve is among the largest restoration efforts of its kind and has the potential to provide many ecological benefits to the Illinois River. It may also provide invaluable information for managers and future floodplain restoration efforts around the world.