North Carolina’s largest lake, infested with carp

Boardwalks meander from the visitor center through a cypress forest bordering Lake Mattamuskeet. Where the forest opens up, 50 snow egrets gather in the canopy. A blue heron screeches above the muddy water and cypress knees sticking out like stalagmites from the swamp below.

As beautiful as these wetlands are, they are part of a beleaguered ecosystem.

Kevin Dockendorf is a Fisheries Biologist with the North Carolina Wildlife Resources Commission. He is standing on a walkway overlooking the Outfall Canal tidal gates. These gates separate the brackish water of Pamlico Sound from the fresh water of the lake.

Dockendorf lowers a Secchi disc, a black and white disc attached to a measuring wire, into the water. The white of the pane disappears ten centimeters below the surface.

“In clear systems,” says Dockendorf, “particularly in a flat system, we want to see two or three feet of transparency, because that’s how far the sun will effectively set.”

A Secchi disk lowered into the seafront of the Tidegates.  The metal carp barriers prevent adult carp from entering the lake.

Zachary Turner

/

for WUNC

Dockendorf lowers the Secchi disk into the sea side of the Watttore. The metal carp barriers prevent adult carp from entering the lake.

The average depth of Lake Mattamuskeet is 1.5 feet. On the sea side of the tidal gate, a two foot gar swims through the sediment and algae. The dissolved oxygen at this port is 0.16 milligrams per liter, which is too low for carp or perch. But Gar and Bowfin breathe with a “prehistoric lung” that allows them to gulp air from above the surface. Behind the gar, a dirty trail forms in a long triangle from the fish’s tail.

Alyson Flynn, an attorney for the North Carolina Coastal Federation, chaired the September public meeting to discuss the plan to restore the Lake Mattamuskeet Watershed.

“In 2016, the lake was placed on the state’s 303 D list,” Flynn said. “The reason it was put on the list was because the chlorophyll ‘a’ and pH of the lake were extraordinarily high.”

For many species, these conditions were a death sentence. In 2017, refugee biologists determined that all underwater grasses, often referred to as SAV or submerged aquatic vegetation, had disappeared from the lake. Without these grasses, water clarity became much worse. Fish also lost vital shelters and nurseries, and toxic cyanobacteria, or blue-green algae, were able to more easily dominate the lake.

A man uses a handheld device to measure the dissolved oxygen in the lake.

Zachary Turner

/

for WUNC

Dockendorf measures the dissolved oxygen in the lake. The water around the carp gate is hypoxic, which means the oxygen levels are very low.

And the culprit for all this devastation?

“When carp get into a system — especially a shallow water system like Mattamuskeet — they can become dominant,” Dockendorf said. “SAV and carp don’t get along, but carp and algae get along well.”

The carp whirls up the ground like a tiller. This action throws sediment into the water column, making the water cloudier. Now sunlight can’t reach the underwater plants, and predators that rely on eyesight to hunt, like the bluegill, can’t see the carp eggs.

So the challenge is to shut down a 4 million pound cutter in a 40,000 acre lake. At least that was the biomass estimate prior to the installation of the carp barriers in March 2021.

The US Fish and Wildlife Service and the NC Wildlife Resources Commission have already taken action to alleviate the carp problem. Commission biologists released bluegill eating carp eggs near carp spawning zones. Refuge workers installed metal carp barriers in the channels. The barrier’s two-inch rods prevent adult carp from sneaking into the lake for hatching.

“In the 1940s and 1950s, the lake went through a somewhat similar situation where refuge management saw a decline in underwater vegetation,” says Wendy Stanton, acting refuge manager for the Pocosin Lakes National Wildlife Refuge. “They also saw an abundance of populations of invasive carp in the lake. So they did massive carp removal in the 40’s and 50’s. They immediately saw an improvement in water clarity. “

Kevin Dockendorf is a Fisheries Biologist with the NC Wildlife Resources Commission.

Zachary Turner

/

for WUNC

Kevin Dockendorf is a Fisheries Biologist with the NC Wildlife Resources Commission.

Stanton said she’d like to see 25 pounds an acre or less of carp in the lake. Although the carp barriers have reduced the overall number of carp, millions of pounds of fish still need to be removed.

This begs the question: what do you do with all that carp?

“Well, we have all this fish biomass,” Dockendorf said. “We have all this protein out there. Common carp were brought to the United States to feed people.”

Although carp have yet to see their culinary moment in the United States, they do have other uses. Carp can be used as an ingredient in animal feed or as a donation to osprey rehabilitation centers.

Although carp could be one of the main reasons for the lake’s water quality issues, the Mattamuskeet Watershed Restoration Plan also addresses issues of hydrology, or the way water flows through the lake.

Michael Cahoon is a local farmer. He represented the Hyde County agricultural community at the September public meeting.

“Much of the farmland I farm flows into Lake Mattamuskeet. [The farmland] been draining into him for years,” Cahoon said. “The lake has a problem that we want to solve. I’m standing there on the side of the fence [believes the lake] needs cleaning and maintenance as has been the case in the past.”

In 1934, a court settled a case between several parties involved in the management of the lake. The resulting document continued to guarantee property owners free access to the lake for drainage.

“If you have a big storm like we’ve had in the past where you got up to 20 inches of water, the pumps may not be able to take care of all that water,” Cahoon said.

Climate experts predict that these large storms will become more frequent with climate change. For some landowners, active management means dredging the canals to keep them clear. But the interest group is also considering other projects. Daniel Brinn, Hyde County’s water and flood control coordinator, represents the interests of the farmers, hunters and residents who depend on the lake for tourism, food and other needs.

One project involves the construction of a wetland on a neighboring landowner’s property.

“This wetland absorbs sediment and nutrients from this water before it is discharged or enters another body of water,” Brinn said.

Improving the water flow in the lake and removing carp will both restore the lake’s water quality and encourage the growth of underwater grasses.

The US Fish and Wildlife Service plans to open bidding for carp removal contracts and hopes the bidding will open before the next carp spawning season in spring 2023.

For more information on the Lake Mattamuskeet Restoration Plan: https://www.fws.gov/project/lake-mattamuskeet-aquatic-grass-restoration

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