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.
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.