SWAN QUARTER — With a lot of nets, some electric stunning, and help from a few “Judas” fish with transmitters, contractors this month are about to launch a roundup to remove a million pounds of invasive common carp from the impaired waters of Lake Mattamuskeet.
The $1 million project, funded by a Bipartisan Infrastructure Law grant, is a critical phase of the ongoing and multifaceted conservation effort to restore the state’s largest freshwater lake. But with an estimated 1 million carp in the lake, weighing an average 4 pounds each, the removal will leave about 75% of the carp to continue its destructive dominance of the ecosystem, at least until another project can be approved and funded.
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“This is going to be a continual issue that we have to address through maintenance efforts once this large-scale removal takes place,” Mattamuskeet National Wildlife Refuge Manager Kendall Smith recently told Coastal Review. “But our goal here is to crash the population of carp. They’re already stressed living in the environment that they do.”
The draft environmental assessment for the carp removal project released in March 2021 had called for removal of 99% of the carp. Although that is not possible yet, Smith said, the refuge fully intends to follow through with carp control.
Situated in the center of rural mainland Hyde County, Lake Mattamuskeet, totaling 63 square miles, is 18 miles long and 7 miles wide. At 40,276 acres, it spans the majority of the 50,180-acre refuge and is remarkably shallow — just 2 to 3 feet deep. Since the 1990s, the condition of the lake has declined precipitously, and the overabundance of carp, which create turbidity in the water, is one of the major contributors to the problem.
“So as bottom feeders, they’re constantly moving along the bottom, sort of filtering through that muck,” Smith said about the carp. “It keeps it suspended in the water column.”
Today, the lake, once a major overwintering destination for thousands of waterfowl, is devoid of submerged aquatic vegetation, lacks water clarity and is plagued with algal blooms from high nutrient levels. Once plentiful largemouth bass, crappie, catfish, sunfish and striped bass have been crowded out by carp or depleted by poor water conditions and lack of food. Many of the waterfowl now visit nearby bird impoundments to feed rather than stopping at the lake.
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Minnesota-based contractor WSB came to the refuge in early December to develop a plan and to catch some of the fish to implant transmitters, Smith said.
“The idea there is carp congregate in the wintertime,” he explained. “And by inserting some transmitters and releasing those fish back into the lake, we can track them later to locate those congregations.” Thus, the fish with transmitters serve as a kind of “Judas” by betraying the location of the other carp.
Smith said that most of the carp will be caught in large-haul seine nets that capture fish from top to bottom in the water column. Other species trapped in the net will be released, and the carp will be loaded onto boats and trucks.
Carp removal had been identified in the Lake Mattamuskeet Watershed Restoration Plan as an important part of an interconnected process to restore water quality at the lake. The 2018 plan, a partnership between the U.S. Fish and Wildlife Service, the North Carolina Wildlife Resources Commission, Hyde County, the North Carolina Coastal Federation and local stakeholders, also recommended science-based approaches to reduction of nutrients in the lake and submerged vegetation restoration.
A similar removal effort in the 1940s and 1950s successfully restored water clarity by removing significant numbers of carp with large-haul seines, baited traps and pound nets, according to a Nov. 13 U.S. Fish and Wildlife press release. More recent efforts employed in other water bodies have used what is known as the modified unified method, which herds fish into large seines. “Once netted, carp are extracted from the lake,” the release said. “WSB will utilize a combination of these removal methods.”
About three years ago, the refuge installed barriers on the tide gates in the four canals connecting the sound to the lake, Smith said. The barriers, vertical slats spaced 2 inches apart, keep adult carp from coming into the lake to breed, but allow other fish and crabs to get through.
Although Lake Mattamuskeet possesses a serene, even mystical beauty, it has not been a pristine environment for a century or more.
“Unlike most naturally formed shallow lakes, Lake Mattamuskeet has been anthropogenically manipulated multiple times throughout its history, resulting in a highly altered morphology and hydrology,” April Dawn Lamb wrote in her 2020 thesis for her graduate degree at North Carolina State University, Informing Common Carp Removal and Submerged Aquatic Vegetation Restoration in Lake Mattamuskeet. “Specifically, repeated attempts to drain the lake for agricultural use reduced its original surface area significantly, the dredging of four outfall canals connected the lake to the estuarine Pamlico Sound, and the construction of Highway 94 in 1940 split the lake into two distinct basins.
“Cumulatively, these events have increased nutrient availability to the main lake, contributed to historical shifts in the primary producer community, and facilitated the development of alternative stable states which persisted until the 1990’s,” she wrote.
Lamb’s research, which provided the carp population estimates for the refuge, found that despite their large numbers, the fish are not thriving. “Broadly, we find that carp in Lake Mattamuskeet are young, fast-growing, and short-lived,” she said.
Most fish were less than 4 pounds and survive about four years; healthy populations of common carp weigh up to 8 pounds and live as long as 20 years. The lake’s high temperatures and pH levels in the summer likely contribute to their relatively puny size and high mortality rate, she added.
Along with a team of subcontractors, WSB, after obtaining the proper permits, is to track the fish, set up various nets, catch the fish, sort the fish, find different markets for the fish, pack and transport the fish, help dispose of unusable fish, among numerous other tasks, all within 18 months.
“We have to surgically implant high-frequency radio tags in the carp, then construct a series of receivers across Mattamuskeet, so we can track those radio-type fish in real time using satellites,” Tony Havranek, WSB’s project manager, said.
So far, the team has inserted 39 fish radio tags, with one kept out to determine the range of detection, deployed seine nets and removed about 900 carp. Havranek had also led operations for the fish logistics company, Erie, Michigan-based FisH20, a subcontractor tasked with transporting the fish to the markets.
Other subcontractors include Four Peaks Environmental Science & Data Solutions, based in Wenatchee, Washington, which will assist with radio telemetry and tracking and Wabasha, Minnesota-based Adams Boat Service, which has worked on several similar state and federal projects in the Midwest.
The tags are about the size of an AA battery in diameter and length, Havranek said.
“We physically push that tag into the carp, and then we thread a wire antenna through the side of the fish and suture the fish up,” he said. The sutures dissolve, and the flexible wire antenna doesn’t inhibit the fish. The battery power source has a tiny circuit board on top. The contractors have handheld receivers to the stationary receivers.
“And then based on the amplitude of the signal or the strength of it, the receiver can can tell approximately where that radio-tagged fish is at in the lake, and then the receiver itself uses a cell modem to send that information back to us,” he said.
Even though “cell service is brutal” at Mattamuskeet, Havranek said, the amount of data is small enough to transmit.
“So I can see it in St. Paul and my partners at Four Peaks in Washington State can see it together in real time,” he said.
A limited seasonal market is available for live carp in New York and Detroit, he said, adding that contractors will also investigate more potential markets along the East Coast. But the bony, somewhat undersized fish is not a popular menu item. They will also be looking for markets for fresh or dead carp, such as for animal feed, fish meal or fertilizer.
“But to be able to even sell carp on that market, especially when you start thinking about the freight costs involved, yeah, it’s really tough,” Havranek said. “We’ve got both live trucks and refrigerated trucks that we can utilize to move fish. But again, the more local places that I can bring those — I thought about crab bait or other types of bait that could be made out of the carp — it’d be really beneficial for a project like this because it can reduce the overall cost based on shipping.”
Fish carcasses could potentially also be used by farmers here, he said. Whatever can’t be marketed would be composted at suitable sites, potentially including uplands on the refuge.
Even though the contract is just for removal of the fish, Havranek said he couldn’t “in good conscience” not help the refuge understand the current carp population by providing updated information, such as the current average weight and length. For instance, he said that from recent sampling it appears that the carp are larger and heavier than what old data had shown.
There is an ecological tipping point — a management threshold — of about 89 pounds per acre of carp, Havranek said. And based on the old data, that would be about 140 pounds of carp per acre in Lake Mattamuskeet.
Smith, the refuge manager, agreed that the contractor’s work will be invaluable in making more effective management decisions, especially with their updated data and their years of experience.
“I think that with this trapping effort we’ll learn a lot more about the population levels and that’s something that this contractor typically does on other lakes and projects,” Smith said, adding that he expects that WSB will make multiple visits during the 18-month contract period. “It’ll be a very adaptive process as they see how successful they are with the initial efforts … and certainly learning what works best and what locations are most productive as they go.”
In recommendations made in her thesis, Lamb suggested that a “suite” of management tactics should be employed at various life stages of the carp, including the canal gate barriers that the refuge has already installed. Other measures to limit repopulation Lamb recommended would be to address potential nursery areas in impoundments and irrigation canals surrounding the lake, add predator fish like bluegill that eat the hundreds of thousands of eggs the carp produce every breeding season, which the refuge has already started doing, and potentially create and manage permanent barriers in canals to trap carp for easier removal.
“To decrease the biomass of adult fish in the lake,” she added, “we recommend conducting yearly carp removals.”
The biological rub is that carp — like another famously resilient species, the coyote — may compensate for reduced population numbers by stepping up their reproduction.
But Havranek said that if their removal project is successful and the refuge implements the other management tactics, the population cycle may be able to be stretched out over a number of years.
“All things being equal, I think it’d be really wise to at least be out on that water body just doing some simple surveys maybe once every three years, something like that,” he said. “That way you can be somewhat proactive in the management piece.”
Whether or not carp actually reproduce more after removal is not necessarily evident to Havranek. But it is clear, he said, that “they can take a beating” by managing to survive stressors in Mattamuskeet that many fish could not — low oxygen, high temperatures, high algae content.
“And they’re still going to be able to find food in some way, shape or form (although) some of them out there look pretty scrawny,” Havranek said. “So I’m sure that they’re somewhat being impacted, but they’ll always just keep coming back.”
