ACTIVE VERSUS PASSIVE MANAGEMENT OF COMMON AND GRASS CARP FOR BACKWATER LAKE 
NATIVE FISH RESTORATION: A CASE STUDY FROM THE NATURE CONSERVANCY’S EMIQUON 
PRESERVE

Greg G. Sass, Kevin S. Irons, T. Matt O’Hara, Thad R. Cook, Michael A. 
McClelland, Nerissa N. Michaels, Melissa L. Smith, and Matt R. Stroub

Illinois River Biological Station, Illinois Natural History Survey, 704 North 
Schrader Avenue, Havana, IL  62644

      Non-native common (Cyprinus carpio) and grass carp (Ctenopharyngodon 
idella) have been implicated for preventing the establishment of submersed 
aquatic vegetation and for negatively influencing the sustainability of native 
fish communities in backwater lake restoration efforts.  The Nature 
Conservancy’s Emiquon Preserve, a >2,833 hectare backwater lake restoration 
effort on the Illinois River, is faced with the dilemma of actively managing for 
common and grass carp with rotenone or allowing native/exotic species 
interactions to determine the success of the restoration effort.  The Emiquon 
Preserve is only rivaled by the Florida Everglades in restoration size, and thus 
serves as an important model to guide future backwater lake restoration efforts.  
We sampled the fish populations of the Emiquon Preserve in 2001 using variable 
mesh-size gill nets, and more recently in the winter of 2006 using a multiple 
gear approach that included mini and large fyke nets, boat electrofishing, and 
gill nets.  In 2001, common and grass carp comprised 20% of the fish sampled and 
represented 2 of the 5 fish species encountered.  Since 2001, anecdotal 
observations suggested that common and grass carp dominated the fish community 
of the Emiquon Preserve.  However, in 2006, we observed a fish community 
dominated by native Illinois River backwater fishes that included members of the 
families Catostomidae (suckers), Centrarchidae (sunfishes), Clupeidae (shads), 
native Cyprinidae (minnows), Ictaluridae (catfishes), Lepisosteidae (gars), and 
Sciaenidae (drums).  Common carp comprised only 9% of the fish sampled and no 
grass carp were captured.  Analyses of length-frequency distributions for the 
native fish species assemblage suggested strong representation of multiple year 
classes and the likelihood of natural recruitment occurring within the Emiquon 
Preserve.  Data from the Long Term Resource Monitoring Program (LTRMP) on the La 
Grange Reach of the Illinois River suggests that the native fish species 
assemblage of the Emiquon Preserve is not reflective of the present-day mainstem 
Illinois River fishery.  Therefore, the Nature Conservancy is faced with the 
trade-off of: 1) actively removing all fish from the preserve in order to 
establish an augmented native fish community; or 2) passively allowing the 
native and unique fish community to remain with carp present.  Evidence from the 
Nature Conservancy’s Spunky Bottoms Preserve suggests that passive management of 
carp may be achievable given certain native fish species assemblages and water 
level management, which may guide managers in future efforts to restore 
backwater lake ecosystems despite abundant carp populations.  

Keywords:  backwater lake, common carp, Emiquon Preserve, grass carp, 
restoration