The Illinois River was once considered a fine sport fishery, home to a variety of native and sport fish populations that attracted anglers from around the region. Then in 1998, researchers learned of a silent invasion underway. Invasive carp (then known as Asian carp) had made their way into the 273-mile Mississippi River tributary and were quickly becoming entrenched in their newfound territory. At the time, few could imagine just how problematic these carp would become.
Flash forward to the mid-2010s. The carp invasion had turned into a full-fledged ecological disaster. Like a swarm of locusts, invasive carp were everywhere. At one point, it was estimated the central section of the river was home to 1,200 carp per kilometer. The carp population had grown so large that they had pushed out many of the native fish populations that, at one time, made fishing on the Illinois River great.
Now, South Dakota researchers are trying to prevent a similar situation from happening here.
Alison Coulter is an assistant professor in South Dakota State University’s Department of Natural Resource Management. She is all too familiar with the situation in Illinois. As a postdoctoral fellow, she conducted research on invasive carp in the Illinois River.
“The Illinois River is the classic case where bighead and silver carp have reached incredibly high abundances and become very problematic,” Coulter said. “In some places, they are over 80% of the biomass in the river. So, if you go out and fish, you’re most likely to catch one of these carp.”
Coulter and her colleagues are working with state and federal agencies to keep invasive carp out of South Dakota’s bodies of water, particularly in Lake Oahe, home to some of the best walleye fishing in the country. If South Dakota sees even a fraction of the problems Illinois faced, there is little doubt the fishing industry’s $271 million contribution to the state’s economy would be severely impacted.
Currently, invasive carp have made their way into the Missouri River, Vermillion River, James River and Big Sioux River. While carp have been found all the way up in Jamestown, North Dakota, physical barriers, like Gavin’s Point Dam, are preventing the invasive fish from encroaching any further into South Dakota — and anglers, researchers, officials and water recreation enthusiasts are eager to keep it that way.
Misconceptions
In the United States, there are two distinct types of carp: common and invasive. Anglers in South Dakota are probably more familiar with common carp, which were brought to the U.S. from Europe in 1831 and were distributed throughout the country as “food fish” by the government. Today, while still technically an invasive species, they can be found in nearly every body of water in South Dakota and are more or less naturalized to the state’s waterways.
Invasive carp, on the other hand, are a much different story.
Invasive carp — a catch-all term for grass, black, silver and bighead carp — are native to Eastern Asia and were brought to the U.S. during the 1970s to help clean commercial stock ponds, aquaculture ponds and wastewater treatment ponds. Flooding allowed the fish to escape, and they eventually found their way into most of the country’s major river basins, wreaking havoc at every turn.
Bighead and silver carp — collectively “bigheaded” carp — are the most common, abundant and problematic types of invasive carp. Bigheaded carp feed on zooplankton and phytoplankton, in direct competition with many native fish species. They eat so much and grow so fast that they not only gobble up most of the available food, but they also quickly outgrow all their natural predators. When bigheaded carp populations become established in a waterway, early research has shown they can — and will — squeeze out native fish populations.
“What we see from other places is that first, you see changes in your plankton and zooplankton, which overall can mean less food for your native species,” Coulter said. “If silver carp and bighead carp are then eating all of this food, then there’s less available for our young walleye each year, and you can see impacts then on the number of native fish that we have, as well as their ability to grow to bigger sizes or in their overall health.”
Silver carp pose a unique problem to boaters as they will leap up to 10 feet in the air in the presence of loud noises (like boat engines). While flying carp are a spectacle, it is not unheard of for these fish to knock water recreation enthusiasts unconscious while out on the water. On the Illinois River, empirical evidence has suggested that boating activities on the river are down, likely due to flying carp.
What can be done?
When invasive carp become entrenched in a waterway, they become nearly impossible to remove. This is why preventative measures are crucial to halting carp invasions before they happen, Coulter said.
To protect South Dakota’s waterways, Coulter and her colleagues in SDSU’s Department of Natural Resource Management have a number of ongoing projects, all in collaboration with officials from South Dakota’s Game, Fish and Parks department.
One of the projects includes modeling flood scenarios along the James River, where invasive carp may be able to expand their range. Another project, led by graduate research assistant Hannah Mulligan ’23, is working to understand the Missouri River Basin’s live bait trade. Releasing live bait is one of the most common ways in which invasive fish — and other invasive species — spread. Identifying potential pathways for how invasive carp can spread is at the heart of Mulligan’s research.
“Anglers should have a good understanding of what the regulations are,” Mulligan said. “For example, in South Dakota you are not supposed to catch live bait for yourself at one waterbody and move it somewhere else. Nor are you allowed to release live bait.”
In Illinois, there is some good news to report. After millions and millions of dollars have been spent on removal efforts, the invasive carp problem is showing signs of subsiding. Just this last December, the state announced it had removed 750,000 pounds of silver carp — in just nine days during an “intensive harvest operation.” Annually, the state is now removing over 1 million pounds of invasive carp from locations along the river.
In South Dakota, it will take a collective effort to prevent further invasion. As a preventative measure, Coulter suggests anglers refresh their knowledge of state fishing laws, best disposal practices surrounding live bait, and identifications of native and non-native fish before getting out on the water next time.
Addison DeHaven
