A new study suggests that invasive silver carp may have stop short of settling in the Great Lakes due to pollution.
Since their accidental release in North America in the 1970s, silver carp have expanded their range in the Mississippi River Basin and have been moving northwards towards Lake Michigan. However, for the past decade, the invading front has not moved past Kankakee.
The possible reason for this may be simply because the fish did not want to enter the polluted waters up north, stopping short of the Kankakee River.
A study on this was published in the Comparative Biochemistry and Physiology Part D: Genomics and Proteomics journal.
"It's a really toxic soup coming down from the Chicago Area Waterway, but a lot of those chemicals go away near Kankakee. They might degrade or settle out, or the Kankakee River might dilute them. We don't really know what happens, but there's a stark change in water quality at that point. That's right where the invading front stops," said co-author Cory Suski, associate professor in University of Illinois' Department of Natural Resources and Environmental Sciences.
The researchers' theory originated from a 2017 US Geological Survey water quality report in which changes in chemistry in a pocket of water was tracked as it travelled from Chicago downstream through the Illinois River. Approximately 280 chemicals had been documented in the Chicago Area Waterway and downstream sites. It was near Kankakee that many of the pharmaceuticals, volatile organic compounds and wastewater indicators dropped off the charts.
In their own research, the team examined gene expression patterns in blood and liver samples from the silver carp taken at three locations along the Illinois River (at Kankakee and two locations downstream).
Based on the results, Suski said, “Fish near Kankakee were turning on genes associated with clearing out toxins and turning off genes related to DNA repair and protective measures. Basically, their livers are working overtime and detoxifying pathways are extremely active, which seem to be occurring at the cost of their own repair mechanisms.”
Such results were not seen in the other two groups of samples, taken downstream.
Whether or not pollution flowing downstream from Chicago is truly the reason silver carp are avoiding the Great Lakes is yet to be confirmed. If their researchers' hypothesis is correct, more research is needed to find out which pollutants the silver carp are avoiding, the answer to which those responsible for fisheries management would be keen to find out.