Is Chicago 'pollution' halting Asian carp?

UIUC study explains why invasive silver carp haven’t moved beyond the Kankakee River

Silver carp leap to elude capture by researchers. (U.S. Fish and Wildlife Service)

Silver carp leap to elude capture by researchers. (U.S. Fish and Wildlife Service)

By Ted Cox

Is Chicago pollution in effect blocking Asian carp from invading Lake Michigan?

That’s the theory posed by a new collaborative study led by scientists at the University of Illinois at Urbana-Champaign. The study, “Physiological Status of Silver Carp in the Illinois River: An Assessment of Fish at the Leading Edge of the Invasion Front,” attempts to determine why silver carp — one of the species of invasive Asian carp — haven’t turned up in the Illinois River beyond its being joined by the Kankakee River well south of Chicago and Lake Michigan.

“It’s a really toxic soup coming down from the Chicago Area Waterway, but a lot of those chemicals go away near Kankakee,” said Cory Suski, associate professor in the Department of Natural Resources and Environmental Sciences and a co-author of the study, in a news release put out this week by the UIUC College of Agricultural, Consumer and Environmental Sciences. “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.

“And this fish never stops for anything,” Suski pointedly added.

Asian carp were released accidentally in the United States in the ‘70s and have been moving up the Mississippi River and now the Illinois River — among many other waterways — ever since. But the migration up the Illinois has been especially troubling in that it’s believed to be a threat to the $7 billion Great Lakes fishery.

Asian carp are perhaps most famous for their tendency to leap out of the water at the activation of an outboard motor or other water stimulation, but their effect on the environment is no joke. They challenge other fish for food and space, they tend to lower water quality, endangering more sensitive species like freshwater mussels, and silver carp feed on plankton critical to mussels and larval fish.

But, with a few exceptions, their course to Lake Michigan has been halted about 50 miles from Chicago for the last decade, and researchers wondered why. According to the UIUC ACES release, the new study was inspired by “a 2017 water-quality report from the U.S. Geological Survey, (which) tracked changes in water chemistry in a single pocket of water as it moved from Chicago downstream through the Illinois River. Right near Kankakee, many of the pharmaceuticals, volatile organic compounds, and wastewater indicators dropped off the charts.”

In short, wastewater “polluted” with substances humans take for granted — hormones, ibuprofen, estrogen, to name just a few — were found at relatively high concentrations on the Illinois River as it traced its course out of Chicago toward the Mississippi, until it was joined by the Kankakee, which diluted it enough to sustain the invasive fish.

But at a cost. According to the UIUC release, “Suski says many of these compounds have been shown in other studies to induce avoidance behaviors in fish, but his team didn’t look at behavior. Instead, they examined gene expression patterns in blood and liver samples from silver carp at three locations along the Illinois River: at Kankakee, approximately 10 miles downstream near Morris, and 153 miles downstream near Havana.”

What researchers discovered was not only that the carp’s livers — charged with filtering out impurities — were being taxed the closer they got to Chicago, it was also altering their genetics.

“We saw huge differences in gene expression patterns between the Kankakee fish and the two downstream populations,” Suski explains. “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. We didn’t see that in either of the downstream populations.”

A map from the study shows its three sampling areas along the Illinois River.

A map from the study shows its three sampling areas along the Illinois River.

“It’s really cool science,” said Kevin Irons, aquatic nuisance species program manager for the Illinois Department of Natural Resources. “They’re under stress. In layman’s terms, it’s genetic stress. The fish are experiencing something that’s not good.

“Their livers are in hyperdrive,” he added.

Irons said of the study that “it’s disappointing they use the word ‘pollution’ here, but really that’s what it is.” It’s really anything that gets flushed down a toilet or a drain, and the main culprits could be flame retardants, psychiatric drugs, birth-control pills, or even just caffeine. “These biological chemicals are hard to filter out,” he added. There could be interactions with agricultural chemicals too.

Both Irons and Suski emphasized that didn’t mean Chicago should be proud of its wastewater and keep it coming down the river to deter Asian carp.

“We’re not saying we should pollute more to keep silver carp out of the Great Lakes. That’s not it,” Suski said. “Right now, things are stable, but that might not always be the case. There’s a lot of work in Chicago to clean up the Chicago Area Waterway. Already, water quality is improving, fish communities are getting healthier. Through the process of improving the water quality, which we should absolutely be doing, there’s a possibility that this chemical barrier could go away. We don’t need to hit the panic button yet, but at least we should be aware.”

Irons added there are always new developments in water treatment, and whatever chemicals are deterring the fish could one day soon be removed before the treated water is dumped into the river, thus removing the chemical deterrent to their movement upstream.

So Irons said IDNR is continuing its efforts to create other physical barriers to bar the fish, as well as a harvesting program that takes a million pounds of the invasive fish out of the Illinois River each year from three different sites: Starved Rock, Marseilles, and Dresden Island. He said that’s lowered their population 96 percent since 2012.

Earlier this year, Gov. Pritzker joined other Great Lakes governors in committing to do all they can to block Asian carp, although they did flinch at the increasing cost estimates for an effective barrier (approaching $1 billion). Irons pointed out there are already three electric barriers set up to deter Asian carp between Starved Rock and Chicago. According to Irons, IDNR will be announcing new measures in the campaign against invasive fish species next week.

“We’re trying to leave nothing to chance. It’s a big issue for us. We are a Great Lakes state,” Irons said, adding, “The risk now is enough to be concerned about, but is relatively low.”