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Two young farmers are proving that open ocean oyster farming off Martha’s Vineyard isn’t just possible — it’s a sustainable future for aquaculture.
It was just before 8 a.m. on a Sunday morning when I hopped aboard a 24-foot Eastern boat with two oyster farmers on Martha’s Vineyard. We headed out to Nantucket Sound, where they’ve sectioned off a tiny portion of ocean to do some very big work.
For Maddie Henson, 26 (and my sister), and Liam Cosgrove, 29, co-owners of Top Shell Oyster Farm, nature dictates everything. That morning, the race was against wind from Hurricane Erin — an unseasonably early August storm. That’s the reality of farming in open ocean waters. “If it’s too windy, we can’t harvest,” Liam explained. For them, the greatest threat is nature itself. Yet working in harmony with the environment is also the essence of regenerative aquaculture — a practice these young farmers want their generation to know about, and advocate for.
The ride to the farm took about 15 minutes. Maddie and Liam moved around the boat in sync, operating with the kind of teamwork that doesn’t require any words. “When we first started in 2021, it felt like we were out here battling the wind and waves. I was nervous all the time,” Maddie admitted. But on this calm August morning, she looked confident maneuvering the boat while Liam prepared the winch to drop a 300-pound cage — holding 5,000 oysters — into the water.
The plan was to fit in one more harvest before the storm forced them off the water for several days. Today’s agenda included dropping two oyster cages and picking up another from where it had been resting 30-feet down on the ocean floor.
At first glance, the farm is nearly invisible, blending seamlessly with the ocean. Yellow buoys outline its two-acre site, while small white buoys mark the oyster cages below. But those markers are fragile; boaters sometimes drive straight through and cut the lines. “We realistically lose a few cages every year, each holding thousands of oysters — mainly due to boat traffic,” Liam said.
Most oyster farms are in bays, salt ponds, or rivers, where waters are calmer and more accessible. When Maddie and Liam launched Top Shell, no leases were available in those safer areas. So they took a risk, and set out to farm over a mile offshore, in waters up to 30-feet deep. They were encouraged and mentored by another local Island oyster farm, Cottage City Oysters, who opened the first open ocean oyster farm in New England in 2014.
Farming offshore required redesigning their gear. Working with Ketcham, a New Bedford-based commercial fishing gear supplier, they created low-profile cages — wider and shorter than the tall, narrow bottom cages typical on the Island. “If there’s a big storm swell, taller cages can tumble, suffocating oysters. Our design keeps them stable and reduces losses,” Maddie explained.
Deeper waters can protect oysters from the rising temperatures that affect shallower areas. For an Island with limited land availability, turning to the open ocean creates an exciting new opportunity for sustainable food production.
On this particular Sunday, the harvest was modest — about 200 oysters to be delivered to an event in Chilmark later that evening. Some days, Maddie and Liam haul up as many as 2,000. Once harvested, oysters head to The Net Result, a seafood market, to be tagged and delivered. This year, Top Shell oysters have made their way to 19 Raw, a popular Edgartown oyster bar. It doesn’t get more “farm to table” than this: straight from local ocean waters to your plate.
As we cruised around offshore, Maddie admitted that she didn’t have a taste for oysters when they first started farming. But she’s come around now, in part because she recognizes the remarkable health benefits of oysters. “Oysters are a complete protein source, containing all nine essential amino acids. Farming them gives us healthy protein without needing more land for traditional farming,” she explained.
The southwest corner of the farm holds oysters presorted and ready for harvest. Liam pointed out that before leasing the site, the underwater area was carefully surveyed by the Division of Marine Fisheries to ensure that the farm's existence would not disrupt the ecosystem in any negative way. He joked that “ecosystem” might have been a bit of an overstatement: before they started the farm, there was only one clam found in the entire two-acre section. The introduction of oyster cages has transformed the area into a thriving underwater habitat in just a few years. Today, eels, crabs, lobsters, conch, fish, and scallops all find shelter and food among the cages.The comparison struck me. These once-empty waters now produce a vital protein source, while elsewhere football field-sized swaths of rainforest are cleared hourly to raise cattle for beef. If there’s a more sustainable way to produce protein, why not embrace it?
On Martha’s Vineyard, oysters need two to three years to grow to market size. Their needs are simple: saltwater, algae, and phytoplankton — all naturally abundant.
Oyster farming is considered regenerative because it actively restores the ecosystems it depends on. As filter feeders that thrive without requiring feed or fresh water, oysters improve water quality, buffer against pollution, and their cages create habitat for other marine species.
Liam attached the winch to haul a cage from the depths. The boat tipped under the 300-pound load as the cage was raised, and I imagined this same process on stormy days, with waves crashing and spilling over the sides. Suddenly Maddie’s early nerves made sense. When the cage finally surfaced and settled on deck, the boat righted itself, and they repeated the process before heading back toward their floating raft to sort.
“Time check?” Liam called.
“9:10,” Maddie replied.
From that moment, the countdown was on. They had two hours to sort oysters by size and quality, placing anything market-ready on ice. The time limit ensures for safe consumption of raw seafood. On the short ride back, Maddie pulled mesh bags from the cages so they’d be ready for sorting.
We arrived at the raft, a 10-by-20-foot floating platform, holding a large sorting table and other farm gear such as mesh bags and extra buoys. Liam opened an umbrella for shade while Maddie dumped oysters onto the table. She prepped tags and ice while Liam sorted. “The main goal is to keep the table full of oysters so Liam can keep sorting. Once I’m organized, I sort with him,” Maddie said.
This efficiency has been honed over five years of working side by side. During the busiest season, they employ local students from the high school, who help sort while learning about regenerative aquaculture. Oyster farming is considered regenerative because it actively restores the ecosystems it depends on. As filter feeders that thrive without requiring feed or fresh water, oysters improve water quality, buffer against pollution, and their cages create habitat for other marine species.
So what makes an oyster harvest-ready? “We like a tear-drop shape, deep cup, thick shell. Three inches is the keeper size. Our oysters are considered medium,” Liam said, shucking one effortlessly, eating it in a single motion. He held up the remaining half shell to the sun, and it looked like a piece of artwork, a creamy white interior with a touch of purple.
Beyond being delicious, oysters are great for the environment. Each oyster can filter up to 50 gallons of water a day, removing excess organic matter and pollutants. They also sequester carbon by converting it into calcium carbonate for their shells — a stable carbon sink that keeps carbon from returning to the atmosphere. Additionally, oysters mitigate nitrogen by filtering excess into their bodies and shells. Staring at the shell in Liam’s hand, I saw more than food. I saw a symbol of nature’s ability to heal, balance, and provide.
Oysters are a complete protein source, containing all nine essential amino acids. Farming them gives us healthy protein without needing more land for traditional farming.
– Maddie Henson, co-owner, Top Shell
What’s next for Maddie and Liam? “Of course, we want everybody to eat oysters — and see them as a sustainable source of food. We’re creating a brand on Martha’s Vineyard to raise awareness and encourage people to eat more oysters,” Maddie said.
That vision includes sharing oyster experiences with both locals and visitors. “This summer we’ve been shucking at private events, teaching guests about regenerative aquaculture and oysters. We also hope to get a new boat to offer farm tours. That way we can bring people out here, show them firsthand what we do,” Liam added.
An oyster farm tour isn’t just about tasting seafood; it’s ecotourism with the power to inspire. Visitors leave with a deeper appreciation for the environment — and a small, delicious way to support it: by eating more oysters.
To keep up with Top Shell Oyster Farm and for the most up to date information on where their oysters are served on Martha’s Vineyard, you can follow Top Shell on Instagram. Next season, you can purchase their oysters from The Net Result. Of course, you can also dine out at 19 Raw and enjoy this farm-to-table dining experience, knowing exactly where your food comes from.
