In the fight against invasive carp, scientists explore a new frontier: stalking babies

For decades, four invasive carp species have devoured plants, gorged themselves on plankton, and endangered an interconnected community of fish, plants and molluscs beneath the brown and murky waters of the Missouri River.

At the same time, environmentalists and officials across the country are fighting to control carp damage: enlisting scientists, installing fences, contracting with commercial fishing companies and even, later this year, by launching a campaign to get more restaurants to serve fish.

Today, scientists from the US Geological Survey and the University of Missouri have identified a potential breakthrough: They are studying the complex way carp eggs move in rivers, in the hope that they can kill while they are still young.

“We have developed better ways to eliminate large numbers of adult carp,” said Duane Chapman, fish biologist at the USGS. “But you also have to think about the other end.”

Carp eggs drift for miles, and as they drift, the fish thrive. If researchers can determine where they land and if those locations are suitable for growing young carp, then they can target the sites and intercept the eggs.

Water moves in three dimensions: downstream, side to side, and top to bottom. But so far, river models have been relatively straightforward, usually based on one or two dimensions, the researchers say. Now, however, they have access to more powerful computers, have spent hundreds of hours collecting new water flow data, and found help – an expert in fluid physics. All of this means that scientists now hope to use three-dimensional data on water flow to trace the trajectory of the eggs.

There are four species of invasive carp found in rivers in Missouri: bighead carp, black carp, grass carp, and silver carp. All are important foods in China, cultivated there for over 1,000 years.

American fish farmers imported them largely in the 1960s and early 1970s to keep fish farms and other ponds clean. But the farmers failed to secure the fish properly, scientists said, and the carp jumped out of the ship, making their way to the Missouri and Mississippi rivers, and spreading rapidly throughout the Midwest.

The population exploded in Missouri in the early 2000s, said Chapman, the USGS biologist.

Adult grass carp consume aquatic plants, which provide food and habitat for native fish. Bighead carp and silver carp feed on plankton, pushing aside native fish that depend on the same food source.

Silver carp are sometimes referred to as “jumping carp,” known to fly up to 10 feet in the air when caught, sometimes injuring boaters.

The black carp have just taken a foothold in the Missouri River. But they do eat shellfish, like mussels, and mussels are already critically endangered in Missouri, in part because of their sensitivity to pollution. Over 40% of Missouri’s 69 mussels are of conservation concern.

The impact is staggering: The US Fish & Wildlife Service estimates that the invasive carp can almost completely wipe out native fish in some particularly affected sections of rivers.

“They are really having an impact on sport fish like walleye and crappie,” Chapman said.

Environmentalists have succeeded in eliminating carp in the lakes. For example, in 2018 at Creve Coeur Lake, government agencies adapted a Chinese technique called “the unified method”: systematically gathering fish with sound and electricity, then catching them in large nets — to remove about 47 000 carp, or 119 tonnes.

Removal from rivers is more difficult.

In 2006, organizers in Bath, Ill. Came up with a creative idea: an annual “redneck fishing tournament,” in which contestants attempt to collect as many silver carp as possible. The trap ? Fishing rods are not allowed – jumping carp must land in boats or be hung in the air by participants as they fly overhead.

In some states, commercial fishermen harvest carp primarily for pet food and fertilizer. Later this year, the State of Illinois plans to launch a media campaign called “The Perfect Catch”, renaming carp in an effort to increase the popularity of fish as a human food, in the same way that 45 years ago, a seafood merchant renamed Patagonian toothfish “chilean”. bar ”to increase its appeal in the market.

But the carp continue to spread.

“They keep invading new places,” said Robert Jacobson, supervising research hydrologist at the USGS. “There are a lot of states that are now very worried about being next.”

Scientists in Colombia have been working for almost two decades to stop the spread.

The USGS Columbia Environmental Research Center is a complex of buildings and ponds behind a chain-link fence. But a lab hosts most of the work with the carp. It is “biosecure” – equipped with a specialized wastewater treatment system with mechanical and UV filters to prevent even the smallest egg from escaping, alive, down the drain.

Inside the laboratory are carp tanks of all sizes, connected by a maze of pipes circulating water through the containers.

One day last month, researchers were experimenting with carp larvae hatched the week before. They placed the baby carp in containers with running water, an important sensory input for the young fish. After three minutes of swimming, the researchers removed the fish and froze them, then dissected their brains to see which areas had been activated by the moving water.

“What we’re trying to figure out is, once these larvae hatch, how their senses develop and how they use them to move around the nursery habitat,” said Amy George, fish biologist at research Center.

The center houses two groups that work on carp, each with 12 to 15 employees. Studies vary. They measure the impacts of toxins on the carp. They develop a large, sterile head with tracking tags, in the hope that when released they will lead scientists to existing populations.

They even mapped the growth of the carp eggs, every 15 to 30 minutes until they hatched, about 30 hours later.

In June, the USGS awarded researchers at Mizzou and the USGS a $ 200,000 grant to use computer modeling and field measurements in the Missouri River to predict how eggs move.

The team has a new member, who brings specific expertise. Binbin Wang, assistant professor of civil and environmental engineering at Mizzou, is an expert in fluid physics and will model turbulence in the Missouri River.

Scientists could even work backwards to calculate where the fish are spawning, which would tell them where to intercept and trap fish larvae, or where to generate turbulence in an attempt to destroy the eggs.

Carp eggs need Goldilocks-type river conditions – not too slow, not too turbulent. Plain water allows eggs to sink to the bottom and die, and fast moving water can destroy them. River managers could potentially harness water dynamics to damage eggs.

The work will also help researchers determine whether uninvolved rivers have conditions conducive to carp survival, and then prioritize resources to high-risk waterways.

Scientists are particularly concerned that carp are traveling north and taking a foothold in the Great Lakes, putting the ecosystem and the fishing industry at risk.

Jacobson, the USGS hydrologist, says their findings will help understand how all kinds of material spread in rivers.

“It’s not just how this applies to invasive carp,” he said. “This also applies to endangered species, and it applies to things like the transport of contaminants – if there was an oil spill, or something like that.”

Now, finally, researchers can gain traction by tracing carp eggs.

“People ask, ‘Why don’t you know more about what these carp are doing? “, Said Jacobson. “Well, because they mostly live in muddy rivers, we can’t really see what they’re doing most of the time.”

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