Biomanipulation of the Largemouth Bass Population to Control Invasive Species and Eutrophication at the Nature Conservancy's Emiquon Preserve

The Nature Conservancy’s (TNC) Emiquon Preserve is a 2,800 ha floodplain restoration effort located in Lewistown, Illinois.  The area is historically significant in that it once maintained two of the most productive backwater lakes in the Illinois River Valley: Thompson and Flag lakes. The area was leveed, drained, and converted into agricultural land in the 1920’s.  TNC purchased the property in 2000 with hopes of restoring it to its natural state.  The area was allowed to naturally flood following a large-scale rotenone of the remnant agricultural ditches to rid the existing water of nuisance and invasive fish species in 2007.  A large piscivore population (mainly Largemouth Bass Micropterus salmoides) was immediately established to reduce the effects of two common ecosystem stressors: eutrophication and Common Carp Cyprinus carpio.  I tested the potential of the Largemouth Bass population to control eutrophication through trophic cascading interactions and Common Carp populations through diet analyses and bioenergetics modeling over the first two years of restoration, 2008-2009.  Largemouth Bass showed a shift in prey use from less profitable prey types (i.e. benthic invertebrates) to highly profitable prey types (i.e. fish) in early July in 2008-2009.  There was evidence to suggest density dependence occurring in 2008, but an increase in lake surface area reduced prey fish consumption (no/ha) in 2009.  Secchi disc transparencies significantly decreased, while Common Carp catches increased from 2008-2010.  Additionally, no Common Carp were collected in Largemouth Bass diets.  My results suggest that the Largemouth Bass population may not be controlling eutrophication or Common Carp populations presently.  Further, 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 used bioenergetics modeling to predict the response of the Emiquon Preserve Largemouth Bass population to various reconnectivity scenarios.  Largemouth prey use in seasonally isolated lakes was similar to both contiguous and isolated lakes, while prey use was dissimilar in contiguous and isolated lakes.  Largemouth Bass inhabiting seasonally isolated lakes consumed more prey fish (W) and fish of greater diversity than in other habitats. The potential for eutrophication and Common Carp control was estimated to be highest in a seasonally isolated reconnectivity scenario at low water levels or high piscivore densities.