116 3rd St SE
Cedar Rapids, Iowa 52401
Several species of invasive carp, formally known as Asian carp, have infamously infiltrated American waterways since their introduction in Arkansas in the 1970s. Floods helped them feather into the Mississippi River and its tributaries — and they’ve been swimming northward ever since.
Iowa spotted its first glimpse of invasive carp around the early 1990s and has been battling them since then, said Kim Bogenschutz, the state’s aquatic invasive species program coordinator. The fish jeopardize native filter feeders such as paddlefish and bigmouth buffalo fish, which feed on tiny suspended food sources like plankton.
Bighead and silver carp are the main species of concern in Iowa. Black carp are edging Iowa’s southeastern border along the Mississippi River at Lock and Dam 19, and grass carp are stocked in some waterways to reduce vegetation.
The Mississippi River’s complex lock and dam system helps stem the spread of invasive carp in Eastern Iowa, but the fish still are scattered across the state’s eastern border and could creep into any interior rivers. Rivers of concern are the Des Moines, Skunk, Iowa and Cedar rivers, said Michael Weber of Iowa State University, who researches fish and waterways in Iowa.
“The rivers all throughout the country are kind of highways for the fish, allowing them to move really big distances,” he said.
Anglers first spotted bighead carp around Iowa City about 20 years ago, and the first silver around 10 years ago, said Paul Sleeper, a fisheries biologist for the Iowa Department of Natural Resources. Silver carp started growing in abundance around Cedar Rapids in the last five years.
“They’re increasing all the time,” he said. “The big individuals show up first, the big spawners, and now we’re starting to see some smaller ones.”
What’s happening now?
Many questions remain unanswered about invasive carp. Typical fish sampling techniques — such as nets or electrofishing — often are not effective for monitoring the species.
To get some answers, Weber and his lab are tracking invasive carp to learn more about their population dynamics: Are the fish weaving in and out of Iowa’s rivers and tributaries? Or are they inhabiting locations year-round?
Ongoing research points to several locations that seem to be sporting more stationary sub-populations of the invasive fish. The lack of mobility could make it easier to control their growth, Weber said.
His lab also is trying to learn more about invasive carp reproduction. In Iowa rivers and tributaries, the researchers use fine mesh nets to catch fish eggs and newly hatched fish larvae that look like “little white squiggly lines,” Weber said. A recently developed app, called WhoseEgg, analyzes the eggs — which can be hard to differentiate between species — and helps predict what fish could emerge.
Knowing more about reproduction habits is critical to stemming the invasion, Weber said. If populations are only reproducing in downstream locations and then swimming north, further growth upstream could be prevented.
“It'd be a lot easier to try to close the door on them and not allow them to move up there anymore,” he said. “But if they're established and able to reproduce (upstream) — well then, we have a whole different issue on our hands.”
Once invasive carp have conquered a waterway, it’s difficult to remove them. The U.S. Geological Survey and Army Corps of Engineers are investigating how to deter continued spread by testing a unique method: a sound barrier.
Researchers are trying to target invasive carp’s hearing by using underwater speakers at Lock and Dam 19, where carp can travel through the lock as barges come and go. By playing different sounds while tracking fish movement, they can see what deters invasive carp while not bothering native fish.
The three-year study began in 2021 and, if successful, will potentially culminate in placing sound barriers in other locations, Bogenschutz said. While other waterways have similar deterrent technology, like electric barriers at the Iowa Great Lakes and barriers with bubbles enclosing sound, the research at Lock and Dam 19 is the only project solely testing sound, she said.
“If we can prevent any further upstream movement of bigheads and silvers ... then we can work our way down starting in Minnesota and try to prevent reproduction,” she said.
As for the waterways already rampant with invasive carp, officials are trying to generate commercial fishing demand for the fish by putting them on the menu.
In June, the Illinois Department of Natural Resources revealed the rebranding of invasive carp as “copi” to help make the fish sound more appetizing. The department also reported that 21 chefs and retailers will put copi on their menus or in their stores, and 14 processors, manufacturers and distributors will sell copi products.
At this year’s Iowa State Fair, there was a fish cleaning and cooking demonstration for copi, Sleeper said.
“People have a negative connotation when they hear carp. They think of a common carp, sloshing around in the mud. These are not like that,” he said. “They’re good quality fish. It’s white meat.”
These combined efforts are unlikely to completely eradicate invasive carp from American waters — but they will hopefully help mitigate their spread, Weber said.
“That's why prevention is really the biggest thing,” he said. “We’re trying to control them at this point.”
● Big Sioux
● Des Moines
● Little Sioux
Brittney J. Miller is an environmental reporter for The Gazette and a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.
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