Invasive silver carp have been spreading throughout the Mississippi River Basin since they were introduced over 50 years ago. However, these fish have not been able to move past a certain section of the Illinois River located north of Kankakee. Research indicates that they are likely steering clear of pollutants found in the Chicago Area Waterway, which flows south before ending near Kankakee.
Invasive silver carp have been spreading throughout the Mississippi River Basin since their introduction a half-century ago. Yet, try as they might, the fish have not advanced beyond a particular stretch of the Illinois River north of Kankakee. Research from the University of Illinois Urbana-Champaign shows the fish are likely avoiding contaminants from the Chicago Area Waterway, which flows south before petering out around Kankakee.
A recent study released in Scientific Reports demonstrates that silver carp alter their behavior and metabolism when exposed to water from the Illinois River north of Kankakee, which represents water from the Chicago area.
“When animals encounter a stressor, they sometimes decide to leave. They might think, ‘This situation is awful, I’m out of here,’ and they escape. However, at other times, they might choose to lower their activity and endure the situation, waiting for conditions to improve. When we introduced the carp to water from the Chicago area, they opted to lower their activity and remained still,” explained Cory Suski, a professor in the Department of Natural Resources and Environmental Sciences (NRES) at the College of Agricultural, Consumer and Environmental Sciences (ACES) at Illinois, and co-author of the study.
Suski and his partners from the University of Texas and the U.S. Geological Survey (USGS) transported water from the Kankakee region to a USGS fish hatchery, where they compared the behavior of silver carp in both water from the Chicago Area Waterway and from controlled laboratory conditions.
“We placed fish in buckets and recorded their behavior with video cameras,” Suski said. “Fish in the lab water would explore, almost as if they were saying, ‘Hey, I’m in a new bucket. Let’s see what’s around!’ Initially, they would become bored and stop moving, but carp in the Chicago area water reduced their activity immediately, indicating they were under stress.”
Interestingly, while carp in the Chicago area water were less active, they were also consuming more energy than those in laboratory water. Suski suggests that this indicates the fish were exerting extra effort to manage their exposure to contaminants.
The behavioral and metabolic results align with a 2019 study by Suski’s team that found wild silver carp sampled north of Kankakee were activating genes associated with toxin elimination while deactivating genes linked to DNA repair and protective responses in their livers. This suggests that the fish prioritized detoxifying pollutants over maintaining their internal repair processes.
Neither study pinpointed the exact contaminants that might be influencing the carp’s behavior, but a USGS report highlights that several pollutants from the Chicago area drastically decrease around the Kankakee region.
“Volatile organic compounds, pharmaceuticals, and many other contaminants are much higher upstream, closer to Chicago,” Suski remarked. “There is a significant shift in contaminant levels right at this specific area of the Illinois River. While carp are proliferating and becoming abundant in other locations, they are absent in this one area, and this phenomenon has persisted for at least the past decade.”
Amy Schneider, the study’s lead author and a former NRES graduate student, stated, “By examining the physiology and behavior of invasive fish like silver carp, researchers can further develop and refine methods to deter these species.”
While it seems that contaminated water effectively keeps invasive carp out of the $7 billion Great Lakes fishery, adding contaminants to hinder carp movement is not a viable solution. In fact, Suski mentioned that recent initiatives to improve the quality of the Chicago Area Waterway have been successful, leading to healthier fish populations. Nevertheless, improving water quality could accidentally remove the natural deterrent that keeps silver carp at bay.
“Enhancing the water quality in the Chicago area is positive, but it’s important to recognize that this improvement might unintentionally eliminate the barriers preventing invasive carp from moving in,” Suski noted. “Continuing research on this topic is crucial to understanding why the population boundary has remained stable for such a long time and what might happen if the deterrent is lost.”
