The nearly-20-pound bighead carp captured in Lake Calumet in June—taken as proof that an
"Asian carp" invasion
had stormed past electrical barriers and was about to overrun the Great Lakes—appears to have been living in the local waters for a long time. The discovery of the carp had worsened a dispute between Chicago and Michigan about whether it would be necessary to shut down commercial waterways and achieve "ecological separation" of the Great Lakes from the Mississippi River Basin.
Now tests on the six-year-old fish by experts at Southern Illinois University Carbondale suggest it wasn't the advance scout for invaders after all:
The tests looked at chemical markers in the inner ear bones, or otoliths, of the fish. Otoliths incorporate chemicals into their structure that are unique to the environments in which they live. They have been used in recent years to reconstruct the environmental history of individual fish or fish stocks.
"The inferences about the environmental history of this fish should be viewed as preliminary and inconclusive given the data limitations and assumptions. But it is very plausible that this fish originated in the Illinois River and then moved or was transported to Lake Calumet or Lake Michigan during the early portion of its life" said Dr. Jim Garvey, director of the SIUC Fisheries and Illinois Aquaculture Center.