ECOLOGICAL IMPACTS OF INVASIVE FISH CONTROL: EVIDENCE FROM ZOOPLANKTON RESPONSE TO ASIAN CARP ARRIVAL AND SUPPRESSION IN A LARGE RIVER

Commercial fishing across the invasion front on the Illinois River has been used since 2010 to stop the spread of Asian carp from the Mississippi River basin into Lake Michigan. The total annual harvest yield has steadily increased to over 300 tons (> 88,000 fish) removed and the upstream distribution has stalled less than 100 rkm from Lake Michigan. While the goal is carp control, this suppression has also produced some positive ecological responses for the native fish and plankton of this large floodplain river. Overall, while abundance and composition of fish and plankton are still altered there is evidence of ecosystem resilience including increases in rotifer numbers where harvest occurs and, subsequently, the rebounding body condition of important native planktivorous fishes. From a theoretical perspective, these results give further evidence of the importance of biotic mechanisms in ecosystems believed to be controlled by physical factors. From a more practical standpoint, we can conclude that ecosystems can be resilient to invaders (at least on a decadal scale) and that control efforts can be an effective management tool for conserving the structure and productivity.