Scientists working to protect the waters of South Dakota from invasive species are calling for people to help out by catching and eating invasive carp—"America's most unwanted fish."
Once established in a body of water, these species can outcompete their native counterparts, and are incredibly difficult to fully remove.
South Dakota State University biologist Alison Coulter and her colleagues have teamed up with local Game, Fish & Parks officials to try to stop invasive carp expanding their range.
They are working to model flood scenarios along the James River, where the carp are already found and that runs downward from north of Jamestown to meet the Missouri River east of Yankton and downstream of the Gavins Point Dam.
The goal is to work out where the troublesome fish might cross into the section of the Missouri River that lies upstream of Gavins Point and harm its native species, particularly walleye.
Two types of carp can be found in the United States: common carp, and invasive carp, which was formerly known as Asian carp.
The former is technically also an invasive species. Common carp were introduced into and distributed across the U.S. from Europe as a "food fish" in 1831.
In South Dakota, for example, they have become so established that they are now considered naturalized to the state's lakes and rivers.
Invasive carp, native to Eastern Asia, are relative newcomers to the U.S., having first been brought over in the 1970s to help clean ponds for aquaculture, commercial stock and wastewater treatment.
Unfortunately, flooding eventually allowed the fish to escape these settings, and by the early 2000s, invasive carp had established themselves across both the Mississippi and Missouri River basins, as well as in rivers across Illinois and Ohio.
Four different species make up invasive carp, and each present a slightly different problem to the local flora and fauna. The most prolific are bighead and silver carp.
Bighead carp eat species of zooplankton and silver carp consume phytoplankton, meaning that they compete with many native fish for resources, and established populations of the invaders can squeeze out their domestic rivals.
"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 in a statement.
She continued: "You will then have feeding conditions for the native fish and eventually that will affect the native fish populations."
Silver carp also have an odd ability that can harm humans enjoying time on the water; they can jump as high as 10 feet (3 meters) into the air.
They often do this in response to the noise of motorboats—with these "flying carp," to use their other name, having been known to smack into boaters and water-skiers and even knock some people unconscious.
The other two species of invasive carp are the grass carp and the black carp. The former feed on aquatic vegetation, threatening the wetlands that serve as home not only to native species of fish but also amphibians, birds and reptiles.
Black carp feed on crayfish, insects, freshwater shrimp, mussels and snails—meaning that they directly compete with native fish as well as birds, otters, muskrats, raccoons and turtles for food.
Coulter is no stranger to the devastating potential of invasive carp, having previously conducted research along the Illinois River, a waterway that is "all but overrun" by the fish.
In the Chicago area, billions are being spent on special barriers aiming to stop invasive carp from making their way into the Great Lakes.
Experts fear that, should the fish establish themselves there, they could disrupt both the commercial fishing industry, which is estimated to be worth some $7 billion annually, as well as the $10 billion tourism industry.
In South Dakota, where Coulter is focusing her research efforts, rising water levels and increased flooding have enabled invasive carp to spread into new areas.
Back in 2011, for example, flooding caused the Missouri River to spill into Lake Yankton—a 250-acre, artificial body of water just downstream of Gavins Point Dam that sports largemouth bass, bluegill, channel catfish and walleye, as is thus popular for fishing.
The flood brought invasive carp to both this lake, which saw fisheries and water quality decline until a controlled kill was undertaken in 2014, and the James River, where silver carp are now so abundant near Yankton, it is "common" for them to jump directly into boats.
Coulter added that, in the James River, "they have found young-of-the-year fish, which means they are probably reproducing with the river.
"They're not a problem anywhere else in the state yet, but if people don't know about them and what they can do, they could become a growing problem."
Another way the fish can spread is via the live bait trade. By releasing fish in a different location to where they were first caught, humans can allow invasive carp to move into new areas.
Anglers in South Dakota, the team's research has revealed, often struggle to tell native and invasive juvenile fish apart, making accidental introductions more likely.
Understanding the regulations is important, noted Coulter, adding: "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."
Even as fishing provides a means for invasive carp to spread, it also offer a way—while not terribly efficient, but potentially quite effective—to help manage the invaders.
And in one piece of good luck, invasive carp have a very mild taste, one said to be on a par with tilapia. This is quite unlike common carp, which despite having been introduced to the U.S. as a food fish, are typically considered rough, with a poor taste.
"That's why you see pushes for people to eat them, because they taste pretty good," Coulter said of invasive carp.
She added: "You are also seeing people developing other products [from them] like fertilizers. There's also dog food and then, of course, cut bait."
Anglers and bow fishers in South Dakota who snag an invasive carp in a location not previously known to harbor the fish are encouraged to report the catch to South Dakota Game, Fish & Parks officials.
Uncommon Knowledge
Newsweek is committed to challenging conventional wisdom and finding connections in the search for common ground.
Newsweek is committed to challenging conventional wisdom and finding connections in the search for common ground.
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Ian Randall is Newsweek's Deputy Science Editor, based in Royston, U.K. His focus is reporting on science and health. He ... Read more
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