The Chicago area waterway is so polluted that scientists call it a “toxic dump,” but that toxicity may be keeping invasive carp from migrating into, and ravaging, the Great Lakes and huge swathes of North America.
That conclusion comes from research conducted at the University of Illinois at Urbana-Champaign. Cory Suski, associate professor in the university’s Department of Natural Resources and Environmental Sciences, co-authored the paper resulting from the first phase of the study.
“Nothing can really stop them,” Suski said. “They can swim through locks; they can swim through dams. So there’s really nothing that slows them down.”
But, he said, the carp have been stalled at one point in the Illinois River south of Chicago for about a decade, and no one understood why they were not traveling farther north.
“A group from the U.S. Geological Survey went out and did some water quality sampling along the same in the same areas where we were sampling fish,” he said. "And what they saw was that the contaminant loads in the water lined up perfectly with the leading edge of the fish and the stress indices that we were seeing.”
Suski’s group tested for possible nutritional reasons, but found none. It did find, however, that the livers of carp at the stopping point showed signs of more intense detox activity than those of fish downstream, indicating that they stop migrating to avoid contaminants.
The U.S. Geological Survey is examining the fish to identify and quantify the contaminants they ingest.
As the river gets cleaned up, Suski said, “We need to be aware of this, because the fish could start moving again in the future if water quality continues to improve – which would actually be a good thing – so if we can understand why they're not moving, then maybe we can make some predictions about why they might move in the future.”