Identifying Recruitment Sources of Asian Carps in the Illinois River

Knowledge of recruitment sources for Asian carps (bighead carp Hypophthalmichthys nobilis and silver carp H. molitrix) inhabiting the upper Illinois River and Chicago waterways would be valuable for directing population reduction efforts intended to supplement electrical barriers in the Chicago Sanitary and Ship Canal and limit the probability of Asian carps invading the Great Lakes.  However, it is unknown whether Asian carps in the upper Illinois River and Chicago area waterways are of local origin or are primarily migrants that have recruited from downstream river reaches.  The extent to which the Mississippi and Missouri Rivers contribute Asian carp recruits to the Illinois River is also unknown.  The objectives of this study are to identify natal environments of adult Asian carps collected from four reaches of the the Illinois River using stable isotope and trace element analyses of otolith cores.  Results to date indicate that adult silver carp collected from the upper Illinois River originated primarily from within the Illinois River itself, but some individuals emigrated from the middle Mississippi River and others recruited from floodplain lakes along the lower Illinois River valley.  Because of the geographically widespread points of origin for individual fish, our results suggest that efforts to substantially reduce Asian carp abundance in the Illinois River drainage and limit propagule pressure on the electric barriers should be directed at a similarly broad geographic scale.