There’s a war being fought amid the vast Mississippi River system. At stake are populations of native fish and a multibillion-dollar fishing and boating industry. Human lives and health are also on the line.
The enemy, two non-native species of fish collectively known as Asian carp, likely number in the tens of millions, experts say. Some are 100 pounds. One of the species, silver carp, wildly flies into the air in fear as boats pass.
“Drivers have been knocked over the back of their seat, so you have a boat going with nobody driving it. I’ve seen it with my own eyes,” said Duane Chapman, a U.S. Geological Survey research biologist based in Columbia, Missouri. “I know there have been broken jaws, and ribs have been disconnected from vertebrae.”
Asian carp have already decreased some native sport fish populations like bass and crappie over 90% in some waters, Chapman said.
Asian carp “eat plankton, so they eat the bottom out of the food chain and things can crash,” said Chris Steffen, Kansas Department of Wildlife, Parks and Tourism’s aquatic invasive species coordinator. He added that a thriving population could be “disastrous” in a Kansas reservoir.
State and federal agencies are taking the fish super seriously.
“In 2020, our budget (for battling the invasive carp) went up to $25 million, up from $11 million,” said Mike Weimer, senior fisheries biologist for the U.S. Fish and Wildlife Service.
A proposed plan from the U.S. Corps of Army Engineers would cost more than $700 million to battle the carp. States are also spending millions: In addition to continued funding of $5.1 million for invasive species prevention and control, $8 million toward costs of an Asian carp barrier in Illinois was part of Michigan’s most recent budget.
Fortunately, progress is being made.
“We’ve spent a lot of money on these fish and learned a tremendous amount of knowledge,” Chapman said. “We’re learning how to control these fish.”
An unhappy history of carp importation
Common carp, which resemble overgrown goldfish, were imported from Europe, where they were popular sportfish and table fare over 150 years ago. Within a few decades, they were competing with native species across the U.S. They also destroy aquatic plants and lead to water quality issues.
But bighead and silver carp were first brought from Asia about 50 years ago, Chapman said. Being plankton eaters, the carp were imported with the hope they could clean waters of unwanted materials, including sewage lagoons.
It didn’t work out that way.
“There’s never been a fish brought in for large-scale aquaculture that hasn’t escaped into the wild,” Chapman said. “Somebody wasn’t paying attention.”
The first escapees were probably in Arkansas and were soon found in the Mississippi River. Populations stayed low for many years and caused few problems.
But that changed in the mid-1990s, when two years of high water gave the fish the long stretches of flowing water needed for their eggs to hatch. And Asian carp don’t need many opportunities.
“One (Asian) carp can lay millions of eggs in their lifetime,” Chapman said.
That results in range expansion up a home river and into another, he said.
After one such high-water year, biologists found a huge school of 3- to 5-inch silver carp in the Kansas River in Johnson County. The most conservative estimate by Kansas Department of Wildlife, Parks and Tourism biologists at the river was at least 350,000 of the young invasive fish in that single school.
Carp in Kansas
So far, Kansas has fared better than many states, thanks to the Bowersock Dam in Lawrence blocking further upriver movement. Silver carp trying — and failing — to jump over the dam are a common sight.
But a roughly 54-mile stretch of the Kansas River, which connects Lawrence to the Missouri River in Kansas City, is packed.
Even if Asian carp make it above the Bowersock Dam, dams at places like Perry and Milford reservoirs should help stop further movement. Asian carp have moved up the Wakarusa River, downstream from Lawrence. But the dam at Clinton Reservoir has kept them from entering the popular fishing and boating lake, officials say.
Kansas has enacted strict laws around gathering and transporting live bait to help prevent the inadvertent spread of young Asian carp, which resemble popular native bait fish like gizzard shad.
Steffen hopes most Kansas lakes lack the long miles of rivers that silver carp need to reproduce. But it could be possible at a few large lakes, like Milford Reservoir, he said.
Missouri’s namesake river is loaded with Asian carp border to border. In many stretches, they outnumber native fish.
As has happened in other states, problems came a few years ago when the river was high enough to wash into 320-acre Creve Coeur Lake, near St. Louis. Desired fish populations, like crappie and bass, plummeted.
The number of carp in the lake was staggering.
So in early 2018, biologists tried an experimental program of using subsurface noise to herd the fish to where they could be netted and removed.
The take was 47,000 silver carp, totaling 240,000 pounds. There was no evidence of reproduction, meaning all of those fish likely came from the river. Desired fish species should recover quickly, Chapman said.
But he fears it would be harder at larger reservoirs, like 55,600-acre Truman Reservoir. With long tributaries, he said it’s feasible Asian carp would reproduce there.
Bigger carp problems elsewhere
The Illinois River holds some of the nation’s highest Asian carp densities, and the fight is on to keep them from reaching the Great Lakes. Should they make it up the Illinois to Lake Michigan, Asian carp could move into the other four Great Lakes. The region’s $7 billion recreational fishing industry could be crippled.
So far, complex submerged electrical fields have been largely successful in blocking Asian carp from the Great Lakes. Increased funding is also allowing biologists to explore ways to tweak existing methods and, hopefully, discover new ones.
“The increased budget allows us to support work that will provide resources that can be used in the five subbasins of the Mississippi,” Weimer said. “What works for (Great Lakes prevention) could very well be applied to other areas.”
Ancient techniques are also in the battle.
In 2014, biologists used rotenone, a natural compound made and used in the Amazon for centuries, to remove a huge population of Asian carp that washed up from the flooded Missouri River into 250-acre Lake Yankton on the Nebraska-South Dakota border in 2011. Within a few years, most desirable species were nearly gone, but gamefish species have rebounded since the carp-kill years ago.
Commercial fishermen are also having success with traditional nets. Some are paid by being able to sell the fish for human consumption or other uses, like bait for crab and lobster traps. Others are getting government funding for removing fish from the edges of expanding populations in an effort to stem that spread.
Carp removal took a huge step forward last winter, when fish-herding with the underwater sounds worked on parts of 160,000-acre Kentucky Lake and nearby 58,000-acre Lake Barkley. Asian carp entered Kentucky Lake via high water on the Tennessee River, and legendary sport fisheries suffered.
With sound systems and nets as long as 2,500 feet, Asian carp were pushed to desired locations and removed.
Success at Kentucky Lake and Lake Barkley is just one reason biologists are gaining confidence battling Asian carp.
Weimer said there’s never been a more organized, better funded coalition of local, state and federal agencies working on Asian carp. Active members come from multiple river systems, lake basins and from dozens of states.
More — and better — ways of battling the fish are expected.
“We’ve only been working on these carp for 20 years. We’re coming up with so many types of tools,” Chapman said. “We’re smarter than the fish.”