A good supply of live half shell oysters and oyster meat is available year-round. Oysters should be bought live and smell like the sea, not sulfurous. Check for freshness by tapping on the shells to see whether they close. The meat from oysters grown off the bottom in farms tends to be higher, making it a good substitute for dredged oysters. Oysters can be kept up to two weeks after collection at 36–38F in a breathable container. Buyers should look for the origin and collection date on a live-oyster shipment, which are required by law. A variety of volume measures are used, so buyers recommend insisting on easily quantifiable units such as by the piece or by the pound. Usually Olympia oysters cost the most, followed by European, Kumamotos, Pacific, and Eastern.
Key sustainability sourcing notes for farmed Eastern oysters from the U.S.:
All farmed Eastern oysters meet a Seafood Watch “Best Choice (green)” recommendation
Total Eastern oyster farms in the U.S. dropped from 399 to 315 from 2005 to 2013
Totally Eastern oyster sales in the U.S. increased from ~$42MM to $68MM from 2005 to 2013
Total Eastern oyster farms in the U.S. dropped from 399 to 315 from 2005 to 2013
Eastern oyster farm decreases by from 2005 to 2013 include: Louisiana from 135 to 18, North Carolina from 35 to 8, and South Carolina from 21 to 6
Eastern oyster farm increases by state from 2005 to 2013 include: Massachusetts from 99 to 123, and Virginia from 18 to 60
Eastern oysters are bivalve mollusks with smooth-edged, oval-shaped shells. Like a variety of other shellfish, they have a two-part hinged shell. The shell has a “cupped” shape, and is white or off-white to brownish in color on the outside and white on the inside, with a purple muscle scar. The shell can have multiple ridges or bumps.
Eastern oysters have fast growth rates and on average, reach up to 8 inches (20 cm) in length. This species of oyster also has high reproduction rates. Eastern oysters reach sexual maturity around seven weeks after hatching and spawn during warm weather. They first mature and reproduce as males, but then later develop as females. Each female oyster has the ability to produce up to 100 million eggs during spawning events, but only about one percent of fertilized eggs move on to the next life cycle stage.
Hours after eggs are fertilized, the larva develop a shell and begin to move on their own. They will find a suitable place to attach themselves, usually on a hard substrate. Eastern oysters are sessile, meaning that once they settle, they will stay in one place for the entirety of their lives. A filter feeder, Eastern oysters eat by filtering plankton and algae from the water using their gills. Oysters have a variety of predators ranging from birds and crabs to anemones, sea stars, and sea nettles. The lifespan of an Eastern oyster varies based on freshwater inflow and predators.
Eastern oysters occur naturally from the Gulf of St. Lawrence, Canada, down the Eastern Seaboard of the United States, to the Gulf of Mexico and Caribbean Islands, to the coasts of Brazil and Argentina. They have been introduced to the US West Coast and Hawaiian Islands, British Columbia, Japan, Fiji, the Indian Ocean, as well as other locations. Eastern oysters are found in estuaries as well as intertidal and subtidal zones where they are sessile. They prefer to attach themselves to hard, rocky surfaces in shallow and sheltered salty and brackish waters. Eastern oyster larvae often attach themselves to the shells of adult oysters, where they will grow together to form large oyster reefs. Oyster reefs provide a suite of ecosystem services such as: providing habitat and protection to other species; minimizing storm surges; stabilizing coastal sediment; improving water quality; and, removing excess nutrients and organic matter from the environment. Eastern oysters can tolerate a higher salinity as compared to other oyster species. Their preferred salinity is 16 to 27 parts per thousand (ppt), but adults can tolerate salinities up to 35 ppt. Spat will not settle in areas less than six ppt. Eastern oysters are generally found in depths ranging from eight to 35 feet (2.4 to 10.6 meters) deep and prefer temperatures between 28° and 90° Fahrenheit (-2.2° and 32.2° Celsius).
Science & Management
The Milford Laboratory at the Northeast Fisheries Science Center (NEFSC) is focusing on ways to enhance growth and survival of shellfish in hatchery settings. NEFSC is using technological advances to study how improvements can be made hatchery operations, while decreasing impacts on the environment at the same time. The center is also trialing certain dietary supplements to see if they can alleviate responses to common stressors in hatcheries.
Ocean acidification can cause a number of changes in seawater chemistry that have potentially harmful effects on a variety of species, including Eastern oysters. NOAA’s Ocean Acidification Program is currently investigating the impacts on ocean acidification on shellfish as well as working to help develop new technology for ocean acidification monitoring systems.
Numerous local, state, and federal agencies are involved to some degree in the permitting process and regulation of Eastern oyster aquaculture in the United States. While there is no national oversight agency for aquaculture in the US, there are extensive regulations in place regarding predator controls, therapeutant use, and disease management. Permitting varies by location with numerous federal agencies providing some degree of oversight. These include:
The United States Department of Agriculture (USDA) – which is responsible for coordinating national aquaculture policy and providing industry with research, information, and extension services;
The Environmental Protection Agency (EPA) – which regulates waste discharge from aquaculture facilities;
The Fisheries and Wildlife Service (FWS) – which regulates the introduction and transport of fish; and,
The Food and Drug Administration (FDA) – the FDA’s Center for Veterinary Medicine is responsible for approving and monitoring the use of drugs and medicated feeds used in the aquaculture industry.
Additionally, the National Oceanic and Atmospheric Administration (NOAA), the US Coast Guard, the Bureau of Ocean Energy Management (BOEM), and the US Army Corps of Engineers are involved in the permitting and management of Eastern oyster aquaculture. Amongst regulations shellfish farms must adhere to include the Magnuson Stevens Fishery Conservation and Management Act, the Endangered Species Act, the Clean Water Act, and the National Environmental Policy Act.
Conservation Criteria - Wild
Impact on Stock
Eastern oysters are primarily found in the U.S., Mexico, and Canada. Factors such as overfishing, disease, and habitat loss have caused Eastern oyster stocks to decline to about 1% of their historical levels. Disease has had a significant impact on the oyster population in the Chesapeake Bay.
Habitat impacts (Wild)
Most Eastern oysters are harvested with bottom dredges. This method can damage marine habitats and reduce biodiversity. Scientists have found that bottom dredging has more of a negative impact on seafloor communities than bottom trawling. A small number of Eastern oysters are raised on suspension systems.
Bottom dredging used to collect Eastern oysters can kill non-targeted species. Since a number of organisms tend to attach themselves to oysters, including several mussels species, they tend to be the primary oyster bycatch, according to the U.S. National Marine Fisheries Service.
In Canada, oyster fishing is subject to seasonal and gear restrictions. Some Mexican oyster beds are controlled by fishermen’s’ cooperatives. The Eastern oyster is managed at the state and municipal level in the U.S. and regulations vary. The Chesapeake Bay oyster fishery is both public and leased, meaning certain areas can be leased for harvesting. Any that aren’t closed as reserves or due to safety concerns are available to the public. State agencies set regulations that govern the area, including gear restrictions, seasonal limits, time limits, and catch limits.
Conservation Criteria - Farmed
The regulations governing oyster farming in developed countries and some developing ones are strict and include best management practices. According to the Monterey Bay Aquarium, farming industry practices tend to be more stringent than the laws that apply to growing shellfish.
Oysters filter water, cleaning it so in some places oyster farming improves the habitat, although this is not universal.
Pacific oysters are the most widely cultivated in the world and they are usually raised on ropes, in trays, or on the ocean floor in coastal and near-shore areas.
Oysters farmed using on-bottom and suspension techniques have minimal impacts on the marine environment. Tongs with long handles and rake-like ends are commonly used to gather these oysters. The dredging of cultured oysters has less of an impact on the seafloor than dredging wild oysters because it’s restricted to relatively small areas. Farmers drag a metal basket containing a row of spiky teeth along the plot to uproot the oysters, causing them to fall into the basket. This dredging carries a moderate risk to marine habitats.
Farmed oysters don’t require feed so there is no loss of wild fish, and they require little or no drugs or chemicals.
Escapes and Introduced Species
Oyster farming has little risk of escapees because they aren’t capable of movement as adults. While some cultured oysters could reproduce in the wild, shellfish producers have stricter management codes than the laws that apply to the industry. The introduction of non-native oyster species to some areas, there have been some negative interactions with wild stocks. Risk of disease transfer is considered moderate because isolating oyster diseases can be very challenging.