Seven Wild Ways Scientists Are Trying to Stop Invasive Carp

Invasive carp are swimming north through American waterways and wreaking havoc on ecosystems. The fish can withstand a variety of environments, survive for decades and lay millions of eggs, which allows them to supplant native species. The filter feeders eat plankton and small fish, outcompeting other fish for food.

In the 1970s, carp were introduced to wastewater and aquaculture facilities in Arkansas as a sort of natural vacuum cleaner to remove parasites and weeds. During a flooding event, carp escaped into nearby waterways. Since then, carp have traveled to every state in the continental United States. Black, bighead, grass and silver carp occupy numerous lakes, rivers and streams. Now, government officials and ecologists are waging a massive battle to keep carp out of the Great Lakes, where they could be devastating. Not only could their takeover be an ecological catastrophe, but a full-blown carp invasion could also be detrimental to local economies by destroying the Great Lakes fishing industry, which produces approximately $7 billion in revenue annually.

“If these fish get in, everybody is estimating that it will devastate the Great Lakes fisheries,” says Jim Dexter, who led the Michigan Department of Natural Resources (Michigan DNR) Fisheries Division until his retirement last month. 

Grass carp have already entered Lake Erie and caused some damage, but other varieties of carp that have not yet been found in the Great Lakes pose a larger threat. Silver carp are perhaps the most notorious because of the uncontrollable above-water flailing they perform when the noise from boat motors disrupts their habitat. A 30-pound silver carp can fly out of the water and hit a boater traveling at full speed with enough force to break the victim’s jaw. To try to keep these invasive carp out of the Great Lakes, scientists, activists and inventors have come up with several innovative methods.

Chefs have put them on the menu

The Illinois Department of Natural Resources (Illinois DNR) renamed invasive carp “copi” this past summer to make them seem more appetizing. The Choose Copi campaign encourages restaurant owners to add carp to the menu. Carp have been a popular delight in China and other Asian countries for centuries. Carp meat is high in protein and low in water contaminants that heavily infiltrate other fish. 

Across the Midwest, restaurant owners are serving up copi tacos, dips and burgers. “It’s so mild, it’s not fishy at all,” Kevin Irons, assistant chief of fisheries at the Illinois DNR, who led the copi rebranding, told the State Journal-Register. “You can flavor it up like a taco meat and it will taste like taco meat. It doesn’t get in the way of any of those flavors. It’s so flexible in how you use it when processed correctly. It won’t even taste like fish.”

The invasive species cookbook Can't Beat ‘Em, Eat ‘Em! includes tasty recipes for at-home copi meals. Officials hope that by creating a consumer demand for copi, more of the species will be fished out of local waterways.

Officials are promoting more fishing

Every year, the Redneck Fishing Tournament in Bath, Illinois, hosts hundreds of anglers for three days and encourages them to catch as many jumping silver carp as possible. The tournament was founded 18 years ago, in response to the destruction of the environment by invasive carp. Anglers boat through the Illinois River and try to catch flying carp out of the air. Last year, the winning team caught 346 fish and the tournament brought in 20,000 pounds of carp.

Some Illinois DNR officials hope that through copi rebranding and increased fishing efforts, carp could be fished down to the point of endangerment in the United States. But Michigan DNR aquatic species expert Seth Herbst says that to fish carp to a point where their population could not recover, around 80 percent of the fish would have to be removed.

“The problem is fishing in general isn’t a very effective manner of removing such an abundant species that has an ability to reproduce very quickly,” says Herbst. 

Once invasive carp are in a waterway, it is almost impossible to eradicate them. State officials would rather spend their resources on preventing carp from further spreading than on managing the populations that have already been established. 

“There is no track record of getting rid of an invasive species. Once it comes in, you end up managing the invasive species, and that becomes another added expense,” says Dexter. “So, the best thing to do is to be proactive, and to keep them out first.”

Government agencies have built electric barriers

In 2013, the U.S. Army Corps of Engineers built permanent electric barriers in the Chicago Area Waterway System to keep carp at bay. The charged barrier, which sits about 30 miles southwest of Chicago, produces 2.3 volts of electricity per square inch. The jolt isn’t enough to kill carp, but it does temporarily paralyze them, so they drift back downstream.

The barriers work well, according to Herbst, but smaller carp can sometimes sneak through them when the electric current is blocked by shipping barges. 

“Sometimes there’s gaps in between those barges that kind of create a refuge for those small fish,” says Herbst. “They’ll actually be able to go past or go through that electric barrier and get pushed upstream.”

The electric barriers have not been completely reliable for other reasons. “There are times when the barriers are not going to be operating at full efficiency,” says Christa Woodley, a senior research biologist for the U.S. Army Corps of Engineers. “That mainly has to do with the fact that you are dealing with something that’s reliant on physics.” 

Woodley says changing water levels and salt concentrations bring challenges. When spring snow melts into the water, the salt sprinkled to treat the roads alters the water chemistry. The dissolved salt ions increase the conductivity of the water, declining the flow of electricity. So some fish feel the zap of the barrier less, and others may not be impacted by the barrier at all and pass freely. Ultimately, this makes electric barriers slightly unreliable. 

The electric barriers also disrupt the behaviors of native fish, potentially impairing their spawning and migration. Even with these problems, scientists are still implementing this method because it is mostly effective in preventing carp from moving upstream.

Engineers are building bubble walls

In Illinois, scientists are working on implementing bubble walls to prevent the movement of carp. The technique, which involves a perforated pipe at the bottom of a waterway shooting up a continuous boil of bubbles, has not been used on a large scale in the U.S., according to Woodley. Such walls block the line of sight for fish. If fish continue to swim into the bubble wall, they face unpleasant sensations and disorientation. Woodley says this makes fish less likely to go through the area. Fish can also hear the bubbling curtain, which Woodley says functions like a warning.

“One of the cool things about bubble curtains is that they work on multiple levels,” she says. 

But scientists also fear that carp will eventually adapt to the bubbles and pass through the barrier without difficulty. And, like the electric barrier, this type of deterrent disrupts native fish. Despite these concerns, scientists and engineers hope to start implementing bubble walls by 2024 in Illinois. 

Scientists are also experimenting with something called cavitation curtains. Normal bubbles get larger as they go up, but cavitation bubbles break apart, and the imploding bubbles feel like a zap to a fish. The curtains also create a noise that is irritating to the carp. 

To feel the effects of this deterrent, fish need to be close to an imploding bubble. This means cavitation curtains must be dense to impact the fish. Unlike bubble barriers, cavitation curtains are not visible to the fish, so the animals are much more likely to swim into the barrier unknowingly. The environmental impact of cavitation curtains has also not yet been studied, and scientists fear that the bubbles could non-selectively kill up to 30 percent of the fish that try to pass through. Because of these limitations, cavitation curtains are unlikely to be used in the near future.

Scientists are blasting the fish with noise

Due to their dangerous habit of jumping when they hear boat motors, silver carp strike fear in boaters. Now, scientists are using this trait against the carp by installing underwater speakers to irritate them. 

“Carp are hearing specialists and should theoretically react to sounds that we’re developing in ways that native fish may not,” says Marybeth Brey, a U.S. Geological Survey fish biologist specializing in invasive species research. “We’re hoping to use that and knowledge about their already existing behaviors to hit their Achilles’ heel.”

Different fish species can hear varying pitch ranges, meaning scientists can blast an unpleasant noise underwater that only carp can hear. The hope is that this might intimidate carp enough to prevent them from moving past a given point. “We’re working on sensory systems and trying to elicit a behavior,” says Brey. “That makes acoustics very promising.”

Efforts to implement acoustics at Lock 19 in Keokuk, Illinois, have already proved fairly successful. But Brey says that scientists worry about the large-scale practicality of this method, because some individual fish are more susceptible to unpleasant noises than others. Also, she worries that the fish might get used to the noise and develop a way to move past the barrier.

Engineers will create a “zone of chaos”

At dams, carp are blocked from swimming upstream. But some dams have locks, which are water elevators that help boats pass. Locks create a weak spot in the system for invasive species to pass through.

At the Brandon Road Lock and Dam in Joliet, Illinois, scientists are working full force to create a "zone of chaos” that will make it nearly impossible for carp to pass through the lock. Starting in 2024, the Corps of Engineers will add acoustic, electric and bubbling deterrents. The $858 million project is still in the planning stage, but officials view the lock as a key battleground.

North of the lock and dam is the Chicago Area Waterways System, which feeds into Lake Michigan. South of the lock and dam is the Des Plaines River, which is fed by the Illinois River. The Illinois River is heavily infested with carp. But past the Brandon Road Lock and Dam, few carp have been found. The goal of the zone of chaos is to prevent the carp from passing the dam at all costs.

“We can hopefully achieve a higher deterrence rate overall when we stack these things together,” says Woodley.

The government is paying inventors to come up with new ideas

In 2017, the Michigan department of natural resources hosted a competition with a hefty reward to anyone who could invent a product that would prevent carp from entering the Great Lakes. The competition, dubbed “Carp Tank,” drew pitches from around the world. 

The top prize of $200,000 went to Edem Tsikata, who came up with the idea of the aforementioned cavitation bubbling curtain barrier. Other winning ideas included a poisoning system, a velocity barrier that could forcefully push fish back downstream, and an imaging and sorting system that would let native fish pass and push away invasive carp.

“We would want to make sure that any given solution wouldn’t also wipe out or dramatically impact the native community, in particular some of the threatened, endangered species that may be in our waters,” says Herbst. “They would be highly sensitive to any one of these given proposed solutions for preventing the spread of invasive carp.”

According to Herbst, the winning ideas are still in the research and development phase, but some are being considered at Brandon Lock and Dam. 

“There’s a lot of smart people thinking about ways to keep [carp] out,” says the Michigan DNR’s Dexter. “To enact these things that are going to do that is going to be very expensive, and it’s going to be something that’s going to have to continue—likely forever.”

Editor’s note: The author’s father works for the Michigan DNR in emergency planning and operations, but had no involvement in the writing of this story.

Carolyn Hagler | READ MORE

Carolyn Hagler is a former Smithsonian intern from Northwestern University.