Foodweb Effects of Asian Carp in the Illinois River

Bighead and Silver Carp are large, planktivorous fish native to Asia, but have become established throughout much of the Mississippi River drainage.  Although Asian carp are present in high densities in the Illinois River, little is known about their effects on native fishes.  Our objectives were therefore to determine changes in food web structure in response to Asian carp in the Illinois River.  We sampled fish communities from high and low Asian carp density sites in the Illinois River and, using stable isotope analysis of δ¹³C and δ¹⁵N, we compared these with historical samples from prior to the Asian carp invasion.  We found that most native fishes at the high density Asian carp site fed at lower relative trophic positions than those at the low density site and from historical samples.  There were also shifts in relative contributions of benthic and pelagic nutrient pathways to the native fish communities.  We propose that these observed effects may be related to Asian carp feeding on zooplankton, resulting in declines in zooplankton trophic structure.  Asian carp thus appear to cause profound changes to food web structure and function in the Illinois River, and have the potential to similarly alter Great Lakes food webs.