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 Pacific oysters from the U.S.:
Pacific oysters are bivalve mollusks with elongated, thick, rough and sometimes sharp shells. The shell is white or off-white with purple streaks and spots. On the inside, the shell is white as well, with a purple hue. Like a variety of other shellfish, they have a two-part hinged shell – one shell is slightly convex, while the other is deeper and cup-shaped. The shells have large irregular, rounded radial folds. If left unharvested, Pacific oysters can live up to 30 years.
Pacific oysters grow rapidly and on average, usually reach 10 to 15 cm in length. They first mature and reproduce as males, but then later develop into females. This species spawns annually during warmer months. As one of the most fecund of oyster species, over half of a Pacific oyster’s body mass is devoted to reproductive capacity. Each female oyster has the ability to produce up to 200 million eggs during spawning.
Larva (also known as spat) disperse throughout the water column and settle on hard substrates. Adult oysters are sessile, meaning they stay in one place for the entirety of their lives. A filter feeder, Pacific oysters eat by filtering plankton, bacteria, microbes and detritus from the water using their gills. Pacific oysters are hardy and can tolerate broad ranges of temperature and salinity - they have been known to out-compete native species because of this.
Pacific oysters are native to Japan, where they have been cultivated for centuries. They have since been intentionally introduced to numerous other countries such as the United States and France. Additionally, China, Korea, other European Union member countries, South Africa, Australia, and New Zealand are all major producers of Pacific Oysters. Pacific 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 waters. Pacific 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. Oyster larvae will also settle on mud or sandy areas when their preferred habitat is scarce. Pacific oysters can be found anywhere between zero and 131 feet (40 meters) deep. Their optimal temperature range occurs between 28.76° and 95° Fahrenheit (-1.8° and 35° Celsius) and their optimal salinity range is between 20 to 35 parts per thousand (ppt). They can tolerate salinities up to 38 ppt, but are unlikely to reproduce at this level.
Science & Management
In 2014, the Northwest Fisheries Science Center opened a shellfish hatchery called The Kenneth K. Chew Center for Shellfish Research and Restoration to support research and production of oysters. Working with the Puget Sound Restoration Fund, the center has the following goals: to culture genetically diverse oysters and preserve local populations; expand the ability to restore shellfish habitat in the Pacific Northwest; advance technology and practices of the shellfish aquaculture industry; improve monitoring to help predict changes in seawater chemistry that may affect shellfish hatchery operations; and understand the impacts of ocean acidification on shellfish.
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 number of species, including Pacific 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 Pacific 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 Pacific 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.
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.