Increasing New Hampshire’s Winter Oyster Survival
Oyster farming is a rapidly growing industry along the coast of New Hampshire. The long, cold winters have always been a challenge, however, and farmers in the state — who harvested more than 1.2 million oysters in 2024 — can lose more than half of their oysters during the winter months. NH Agricultural Experiment Station scientists Easton White and Brittany Jellison, both assistant professors of biological sciences, are collaborating to investigate exactly why so many Granite State oysters never live to see spring and what can be done to improve their chances and boost farming profitability.
Oysters thrive in the relatively warm, briny waters of New Hampshire’s estuaries during spring, summer, and fall. In winters, they slow their metabolic processes to near zero, making it possible for them to survive on dry land and providing an opportunity to improve their winter survival rates. White is studying what happens to their biological processes during dry-land dormancy and how to maximize survival away from the icy waters.
Winter along the New Hampshire coast holds many perils for oysters.
“During winter, New Hampshire oyster farmers usually have to drop their oyster beds into deeper water, where they’re susceptible to marine worms and other pests and predators,” says White. “But oysters can survive for months out of water in cool, damp conditions, and we’re studying exactly which on-land environments are best for oyster health and yield the highest survival rates.”
Joe Rankin, who runs Hidden Coast Shellfish, a New Hampshire oyster farm based in Little Bay, is excited about the potential impact of the research.
“We have observed winter mortality rates ranging from a ‘best-case’ of 25% to as high as 80%, which can effectively wipe out a year of work,” he says. “This is why the research being done in Dr. White’s lab is vital. By keeping oysters in a controlled environment for four months, we can protect them from threats like extreme temperatures, predation, biofouling, and ice.”
Solving the Dormancy Puzzle
The research, underway in controlled conditions within new cold room facilities at UNH, is looking at two pieces of the aquaculture puzzle. The first puzzle piece is figuring out what oyster farmers can do now to improve their harvests. In White’s lab, graduate student Kaila Frazer is looking at how different management strategies affect survival rates.
For example, pilot experiments include assessing whether burlap coverings can help by retaining moisture in dry storage, how stressing the oysters by shaking them from time to time affects them, and finding the best time to transfer them from dry storage back to wet conditions in the spring.
“We’re doing exploratory pilot projects from a single site now to see what happens during dry storage and are working with the physiologists to explore why they happen,” says Frazer. “In the future we hope to work with multiple farms so we can see if growing sites make a difference, as well as introduce other variables into our research.”
Measuring the heart rates of dormant oysters.
The second puzzle piece is the actual physiology of oysters in cold conditions out of water, which is being investigated by Jannine Chamorro, a postdoctoral research associate in the White lab, and Maggie Dillon, a graduate student working with Jellison. They are studying how an oyster’s biological processes change when it throttles down in the cold, and whether they remain consistent as an oyster ages.
“I’m studying how dormant oysters use energy and how that might affect how well they respond to different overwintering strategies,” says Dillon. “Once we know more, farmers might be able to help them build up the right kind of energy stores to help them survive winter more easily.”
Understanding the basic biology of what happens during dormancy and the effects of different methods of cold storage will provide important insights about how farmers can best manage winter environments to reduce losses.
“We conducted our first dry storage overwintering project last year, and it’s the first time that physiological data such as heart rate was collected for dormant oysters outside of cold water,” adds Chamorro. “As the project moves forward, we’ll be able to put the pieces together about what’s happening in the oysters and how to support high survival rates.”
Future possibilities
Between 2014 and 2024, the value of the oyster aquaculture harvest in New Hampshire grew by 553%, providing an economic contribution of $5.95 million within the state in 2024 alone. Much of New Hampshire’s oyster farming takes place in Little Bay, a shallow tidal estuary that allows for relatively easy access to submerged cages. The small geographic footprint of the industry may provide opportunities for farmers to pool resources for transportation and cold storage operations.
“In the end, it’s a collaboration between UNH and the farmers,” says Dillon. “We’re in the ‘diagnosis’ step’ now. Based on our findings, we can then figure out how to shape gear and practices to best help farmers meet their needs.”
A cold storage unit that provides optimal conditions for overwintering oysters need not be massive to accommodate many of them, especially if high density bagging is found to be good for dry storage survival.
“If this research continues to prove successful, it will allow the industry to grow by increasing farming efficiency and shellfish landings without needing to over-permit the state’s limited waters,” says Rankin. “Our goal is to expand aquaculture responsibly, ensuring our coastal waters remain a shared resource for the entire New Hampshire marine community.”