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April 4, 2012
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The Oyster Connection

by Dr. Heather Deese and Catherine Schmitt

In Maine, oysters are grown in the water column in order to protect them from predators.
In Maine, oysters are grown in the water column in order to protect them from predators. Photo: Catherine Schmitt

Say the word “oyster” and most people will think of the Chesapeake Bay or Louisiana. But Maine has oysters, too, and the expertise that has developed over the last 40 years of Maine’s evolving oyster industry is now in demand in more traditional oyster regions.

American or eastern oysters grow in estuaries from Canada to Texas, but the majority of oysters are landed in the Gulf of Mexico, with 15.7 million pounds valued at $54.5 million harvested in 2010, according to the U.S. EPA. Oyster populations cycle in response to changing river conditions. Along Louisiana’s coast, the timing and amount of fresh water from the Mississippi determines larval output, and later, the settling success of juvenile oysters. The animals have developed seasonal spawning patterns attuned to the rivers’ flow—ripening throughout the winter, and spawning in April, May and June during the typical spring “freshet” when snowmelt and spring rainwater arrives in the Gulf. Again in the fall, oysters spawn in chorus with the secondary seasonal flow peak.

Oysters thrive in the narrow band of water that is fresher than seawater, but saltier than freshwater. The balance of fresh and salt drives the oyster’s life. Too much freshwater (below 10 parts per thousand or two parts fresh water to one part salt water) and oysters will not spawn. On the other hand, too little fresh water leaves oysters vulnerable to the marine predators and diseases prevalent in pure seawater.

Oyster fishermen in the Gulf of Mexico, where Mississippi River flows exert a strong influence on oysters, schedule their harvests around these seasonal changes.

When the Gulf of Mexico oyster season opens, typically on the Wednesday after Labor Day, fishermen travel to the reefs to harvest oysters for the market (“sacking”). However, a unique characteristic of the oyster beds in the northern Gulf of Mexico is the extent to which they are actively managed by oystermen who consider themselves farmers. Since the early 20th century, Louisiana oystering families have held leases that give them the exclusive right to harvest off particular areas of seafloor.

Fishermen who hold these leases usually spend the fall dragging wild seed oysters from public reefs for “bedding” or placement on their lease areas with high pressure hoses attached to their boats. The transplanted oysters take about 18 to 36 months to grow to market size. After fall seeding, some oystermen fish public waters through the winter until the season closes April 1, and then they return to their leases for the summer. Seeded leases yield an average return of 35 percent, so most individuals or groups hold several leases in different areas around the Delta to hedge bets against natural variability.

Fishermen from other places don’t see at this as farming. But transplanting and seeding can reduce pressure on wild oyster reefs and allow fishermen to time their harvest around market conditions.

For over a decade, John Supan, an oyster biologist with Louisiana Sea Grant, has been breeding for a triploid, disease-resistant oyster that he hopes Louisiana fishermen will begin using in caged grow-out to produce an oyster that will be in harvestable condition during the summer and fall. Oysters grow full of creamy, heavy fat when they are not breeding, which is during the winter for wild oysters in Louisiana. Dr. Supan’s triploid and tetraploid oysters are almost 100 percent sterile, so they will retain a higher meat yield and quality through the summer and into the fall.

He hopes this oyster will spur development of a supplementary off-bottom caged grow-out fishery, which could provide more stable seasonality for fishermen with a summer or fall crop. They could also grow faster than the wild diploid oyster, from a microscopic egg to harvestable in 12 to 15 months, partially because they would be exposed to more concentrated food in cages suspended in the water column, and are bred to be resistant to dermo, one of the more deadly diseases that affects Gulf oysters.

Scientists, extension professionals, and fishermen from Louisiana are looking to Maine, where oyster aquaculture has experienced success, to learn how to extend fishermen’s exclusive rights over oyster reefs on the seabed to allow for contained culture in the water column.

While Louisiana leaseholders have the right to access oyster reefs, they have no legal rights to the water column above their leases. In Maine, aquaculture leases include the seafloor and the water above it, allowing growers to place cages, floats, or other systems anywhere above bottom where their seafood product will grow best and be protected from predators. From his position developing a new breed of disease-resistant oyster that could transform the already booming oyster industry along Louisiana’s coast, John Supan is hoping he and his fellow Gulf Coast residents can learn from Maine’s oyster-growing techniques and legal mechanisms. “We’re going to need whole new laws for this,” said John Supan. “We’ve got a lot to learn from Maine.”

This article is made possible in part by funds from Maine Sea Grant.

Heather Deese holds a doctorate in oceanography and is the Island Institute’s vice-president of programs. Catherine Schmitt is communications coordinator for Maine Sea Grant.

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