North Carolina’s oyster industry is worth nearly $25 million. That’s according to the North Carolina Coastal Federation and the state Division of Marine Fisheries. The Federation and its partners have a goal to build the industry to $100 million by 2030, but there’s one hurdle that threatens farmers up and down the coast.
"For the last like four years in Stump Sound, there have been these events soundwide essentially, where a giant mortality happens,” James Hargrove, an oyster farmer in Wilmington, said.
Hargrove owns and operates a small farm. He started it in 2016. It's just him and two employees who plant a million oysters each year with the hopes of a big crop. But when it comes time to harvest them, they sometimes find close to 90% have died off.
"It's been really disappointing,” he said. “There's a lot of work that goes into it. It takes about a year before the oysters are ready to go to market, sometimes longer than that."
Hargrove said it can take up to two years to recover from these losses. It’s a risky business, with impacts from storm events and keeping the oysters safe from unwelcomed plants and animals being factored into costs. There isn't much relief, though, as these mortality events are common. Tal Ben-Horin is a researcher at NC State's Center for Marine Sciences and Technology, or CMAST.
"Every farmer in North Carolina has been impacted by this in some way," Ben-Horin said.
Ben-Horin has been working with farmers to understand these mass mortality events.
"The scale of mortality that we see impacting these farmed oysters is just beyond anything you really see in wild populations,” he said.
He and other researchers around the state have been chipping away at a list of potential causes. As a pathologist, he's so far ruled out parasites or pathogens as the primary culprit. Ben-Horin has come to the conclusion that genetics are likely a major factor.
"The genetic stock seems to be really important for impact," he said, adding that finding comes from a study in which his team experimented with commercial and wild oysters from different genetic lines. "What we're seeing is some of the North Carolina genetic lines do a bit better with respect to that mortality here, so it seems like the genetics really matter."
In short, locally-sourced oysters perform better than non-native ones. That's a key takeaway, as most of the seeds used by North Carolina farmers come from stock in Virginia. Ben-Horin and Hargrove say that's because Virginia's modern oyster industry has been around for much longer, so it has the infrastructure to mass produce seeds and export them along the East Coast.
While genetics seems to play an important role, it's not the only factor. Ben-Horin has examined mass oyster casualties up and down the East Coast and in the Gulf.
"In North Carolina, the environmental risk factors do seem to be high salt and warming periods, but that is not true across the board, which just makes the puzzle even more complicated, he said."
Juliet Wong is a researcher at the Duke University Marine Lab in Morehead City. She's beginning a small-scale study that will observe environmental conditions across two locations -- one farm operated by Duke, which has performed well in recent years, and another at NC State, which has suffered several mass mortality events.
“We're measuring temperature, oxygen, pH, salinity. Just checking in the bags where the oysters are so we can understand the water conditions they're actually experiencing inside of the bags," Wong said.
At Duke’s farm near Fort Macon, a few dozen mesh bags float on top of waist-high water. Each bag contains 50-200 oysters. Her research includes not only measuring environmental factors, but also the density of oysters in a bag and how often they are flipped. Through the brackish water, Wong works her way around to record the conditions in each bag.
"The idea is that we'll have collected continuous data about environmental conditions, sort of leading into that event. We're looking to see if there's anything out of the ordinary leading into a large oyster mortality.” Wong said.
Andrew Barfield, a research assistant, pours one bag out into a bin and begins checking for dead oysters.
“So we haven’t experienced any significant mortality yet in any of our genetic lines,” he said.
When I visited the oyster farm, it was June, a little before mortality events are usually recorded.
One limitation of Wong's study is its size -- just two farms are included. Another is that the oysters being studied are not the same as the ones grown in commercial farms. The ones on Duke’s farm are known as “big uglies.”
These have had a lot of oyster that have settled on top of their shells, so that’s why they look disjointed and in clusters,” Barfield said. “These ones are a little bit older, a little bit bigger, and a little bit bigger than some of the other ones we have out here.”
Nonetheless, Wong says tracking the data over time will help pinpoint environmental conditions that put oysters at risk, native or nonnative.
As the oyster industry navigates these challenges, farmers like James Hargrove remain committed. Despite the setbacks and uncertainty, he continues to plant new oysters.
"We're resilient. If there's anything in oyster farming it's resiliency, so if you're not resilient, you shouldn't even try," Hargrove said.
North Carolina's modern oyster industry is still relatively young compared to its neighbors, and it has seen rapid growth over the last decade. Hargrove says the industry is experiencing growing pains and that these mass mortality events only make it harder for small farmers like him to thrive. The path forward, he says, will include continued research, as well as farmers who are willing to adapt their practices in response.
