Last spring I worked on a report on the impacts of oyster acidification on the Eastern Oyster (Crassostrea virginica) population in the Chesapeake Bay. To get some background information on the oyster growing process, I visited with a neighbor who harvests oysters for consumption on Antipoison Creek. I wanted to share some pictures and my understanding of the oyster farming process from that project.
Farmer Mike grows over 40,000 oysters, off of his shore and dock, and further out, in the creek and Chesapeake Bay. Mike buys oyster larvae from a nursery outside Mathews, Virginia. The nursery produces Dermo-disease resistant triploid oysters. (A good story on the creation of triploids, and their differences from diploid oysters is here: Chesapeake Quarterly).
The larvae are raised in tanks, like the empty one above. When larvae attach themselves to a hard surface, which they must do to grow, they are called spat. Many farmers use a spat-on-shell approach; spat grow on oyster shells until they form their own shell, and are large enough to be moved. (Spat are less than 0.98 inches long; it can take up to a year for oysters to reach this size).
The oysters are then moved to a net or strainer, shown above. Mike keeps the strainers in floats, suspended in the creek and attached to his dock.
As the oysters grow, they are moved to larger cages, placed on the bed of the creek, and further out in the Bay. Separating oysters into cages at this stage reduces overcrowding and competition for food. It generally takes 2.5 – 5 years for an oyster to grow to market size ( 3 inches or longer). At this time, the oysters are collected, transported, and sold to local restaurants and markets.
Other interesting facts about the oyster farming process:
- Spawning occurs from May to September- water temperature must be between 64-68 degrees F.
- Oysters become dormant in colder water temperatures; they can survive freezing temperatures, if left submerged in water
- Oyster growth is dependent on salinity, water quality, water depth, temperature, and the presence or absence of disease, predators, sedimentation, food source
- Farmers, like Mike, must frequently test water quality, including dissolved oxygen levels, and concentrations of chlorophyll, which provides nutrients for oysters
- The oyster can grow up to 8 inches long, but is usually sold for consumption at 3 inches
Further reading on the Eastern oyster: NOAA.
Raising oysters requires a great deal of care throughout the year. I found a site on cage handling and maintenance that has seasonal instructions for raising oysters, and additional info on the farming process. (Severn River Association).