Oysters
Oysters are bivalve mollusks from several different families that live in saltwater habitats. In this article, we will be looking at true oysters, which are in the family Ostreidae. In the Pacific Northwest, we have one native oyster species, the Olympia oyster, and several other species that were introduced for aquaculture purposes.
Oysters are filter feeders that form large reefs. They have a positive impact on their environment. They filter water and improving water clarity, and the reefs create a buffer against strong waves hitting the coast. These reefs create habitat for other sea life similarly to coral reefs by increasing the habitable surface area that other organisms, such as fish, crustaceans, and shellfish can use.
Humans have been harvesting and eating oysters since prehistory. Evidence of oyster consumption can be found in the large oyster middens, or piles of discarded shells, that are found around the world where humans had a presence. Oyster harvesting has been a major economic activity in suitable coastal regions throughout most of human history, and continues to be so today.
Oyster farming
For most of history, the main method of collecting oysters involved harvesting them from wild reefs.
With the advent of the industrial era, oyster harvesting exploded in many regions, putting pressure on wild populations. In addition, the the rapid urbanization of estuarine regions led to the pollution and habitat destruction of natural oyster reefs.
Starting in the mid-1800s, many natural oyster reefs were overharvested, especially with the use of mechanical dredges. Dredges, which are essentially large steel rakes that are dragged along the reef bottom, are especially destructive to oyster habitat. By the early 1900s, wild oyster populations had been depleted throughout Europe and both sides of the United States. By 1920, up to 75% of the Chesapeake Bay’s oyster reefs had been destroyed. In the Pacific Northwest, the native Olympia oyster was extirpated from large portions of its native range by the early 1900s due to overharvesting and pollution from mills. In Europe, the native flat European oyster nearly went extinct, and has yet to recover. As an example: in London, in the 1860s, nearly 700 million oysters were consumed, but UK landings dropped to 40 million in 1920, and to 3 million in the 1960s. Today, both in the Pacific Northwest and in Europe, the majority of the oysters harvested commercially are a Japanese species, the Pacific oyster, introduced to replace the decimated native populations.
With the destruction of wild oyster populations and their habitats around the world, people increasingly turned to aquaculture to produce oysters.
Oyster farming is actually a very old practice, having been first pioneered by the ancient Romans as early as the first century BCE. Today, most of the oysters consumed in the world are farmed oysters.
Current farming methods
In modern oyster farming, oysters are cultivated in a few different ways. When oysters reproduce, they produce free-floating larvae. Once these grow large enough, they attach themselves to a surface. Methods of growing oysters differ mainly in the surface the oysters are attached to.
There are two main approaches to oyster cultivation. With the first approach, oysters deal with environmental and predator pressures. The second approach is suspend the oysters above ground to keep the oysters away from mud, tides, and predators.
Bottom-cultured and longline-cultured oysters fall into the first camp. Although there are losses from predation and exposure to the elements, these methods result in sturdier shells and firmer meat. For bottom-cultured oysters, oyster seed is distributed in existing oyster beds and collected similarly to wild oysters. With longline-cutlured oysters, they are suspended on long ropes, but still deal with environmental pressures.
With the second approach, racks and bags, cages, trays or nets are used to suspend the oysters above the ground. The advantage is that they are protected from predators and do not have to filter as much sand and mud to feed, which allows them to grow faster. However, they tend to have brittle shells and meat that is less firm. On some farms, suspended oysters are also tumbled or exposed to a rougher environment during their development to gain some of the benefits of bottom-culturing and improve the shell hardness and meat of the oysters. These tend to be newer methods.
Oyster farming in the Pacific Northwest
Although oyster farming takes place throughout the Pacific Northwest, Washington is truly the center of the industry, with over 300 growers in the state that produce more oysters than any other state in the U.S. The natural geography of the Willapa Bay and the Puget Sound regions have many protected bays and inlets, which are well-suited to raising oysters. By contrast, Oregon’s coast is much more exposed, so oyster farms were limited to calmer bays: Netarts Bay, Yaquina Bay, Tillamook Bay, and Coos Bay.
Oyster harvesting in Washington and Oregon took off in the mid-1800s due to increased demand from San Francisco. Originally, the industry was focused entirely on harvesting wild Olympia oysters, but as it developed, farming was introduced. In the late 1800s, small dikes were built in oyster-producing areas in Washington to keep the Olympia oysters submerged, protecting them from cold in winter and heat in summer. The dikes also allowed the oysters to be grown in areas they could not previously be. Like other oysters in the genus Ostrea, the Olympia oyster tends to live continually immersed in water, in contrast to oysters in the genera Crassostrea and Magallana, which prefer to live in the intertidal zone, where they are exposed to air at low tide. With the disappearance of Olympia oysters and the rise of Pacific oysters, the dikes fell out of use.
As issues arose with the decline of Olympia oysters in the Pacific Northwest, farmers turned to different species of oysters to replace them. Early attempts were focused on Virginia oysters, but these were poorly suited overall to the local climate. Around the 1920s, Pacific oysters were introduced from Japan. These were much better adapted to the region. Today, they make up the majority of the oysters grown in the Pacific Northwest.
Cooking with oysters
Oysters are often eaten raw, “on the half shell”. They are also cooked: grilled, steamed, battered and fried, or baked. Oysters are commonly canned or preserved by smoking or pickling. In my opinion, the best use for an oyster often comes down to its size: smaller oysters are better eaten raw, whereas larger oysters excel when cooked (of course, this comes down to personal preference).
Shucking oysters
Like other bivalves, oysters respond to threats by closing up their shells. Oysters should not be eaten if they are dead, as they spoil rapidly. Oysters should be checked before cooking. Live oysters will close up when pressed.
Therefore, to eat them raw, oysters have to be shucked, or opened with a special knife. Shucking knives comes in different shapes and sizes. Different styles of shucking knives are better or worse at opening the various types of oysters for sale.
To shuck an oyster, you want to get the knife between the two shells to cut the adductor muscle that holds them together. The most common method is to insert the knife at the hinge. Once the hinge is separated, run the knife along the shell to cut the muscle. This method works best with smaller oysters with harder shells. Shorter, squatter knife styles work better for hinge shucking.
The other method is known as bill or side shucking. Here, the knife is inserted on the between the shells on the other side, where they are thinnest, and the muscle is cut from there. This method works better for brittle shells and larger oysters. A longer knife, such as a Chesapeake shucker, is recommended.
To reduce the chances of the knife slipping and potentially cutting yourself, it’s best to use a towel to hold the oyster or to wear a protective glove. Do not apply too much force when opening an oyster, as it increases the chances of slipping and breakage of the shell. Be careful not to lose the liquid inside the oyster, known as the “liquor”, as this holds a lot of the flavor of the oyster.
Oyster safety and seasonality
Because shellfish consume phytoplankton, there is a risk that they can accumulate naturally occuring toxins that can cause shellfish poisoning in humans. As a result, state organizations monitor the risk of outbreaks and regularly test commercially-produced shellfish for toxins. The risk is much higher during the warmer summer months, which is why it is often recommended to eat shellfish, including oysters, during the cooler months. Quality is best from September to April. However, oysters are produced year-round on farms here in the Pacific Northwest, so ultimately, you can eat them whenever you want as long as they are from a reputable source.
Species
Oysters
Olympia oysters (Ostrea lurida)
Pacific oyster (Magallana gigas)
European flat oyster (Ostrea edulis)
Virginia oyster (Crassostrea virginica)
Kumamoto oyster (Magallana sikamea)
Olympia oysters
The Pacific Northwest is home to one native species of oyster: Ostrea lurida, the Olympia oyster. This is a strong-tasting species with a coppery flavor. Olympia oysters are rounded, grow to an average size of only 1.5 inches. They are the smallest species we have.
Harvesting of Olympia oysters exploded in the mid-1800s due to demand in the San Francisco Bay Area following the gold rush, and they were nearly wiped out in many parts of their native range due to overharvesting and pollution from pulp mills. They have been brought back from the edge of extinction and are once again found throughout their native range from Alaska to Baja California, but their population is drastically lower than it was historically. Today, they have been mostly replaced in farming operations by the Pacific oyster, Magallana gigas, which has also naturalized in the region and competes with the Olympia oyster for habitat.
Currently, there is limited production of Olympia oysters in the Pacific Northwest. They are much slower-growing and smaller than Pacific oysters. As a result, farmers are less inclined to grow them. However, efforts have been undertaken by organizations such as the Puget Sound Restoration Fund to restore Olympia oysters to their native habitats and previous population levels.
Pacific oysters
The Pacific oyster, Magallana gigas, is the economically most important species of oyster in the world, accounting for some 97% of the farmed oysters harvested in the world. It has made up the majority of U.S. landings since 1977. Washington is currently the largest producer of Pacific oysters in the United States, accounting for over half of total production. Willapa Bay, in particular, is the center of oyster farming in Washington.
Pacific oysters originate in eastern Asia, from Russia down to China. They were introduced from Japan in Europe and the United States to replace suffering stocks of native oysters in the late 1800s and early 1900s. Today, they are found around the world. In Washington and Oregon, Pacific oysters were introduced around 1919.
M. gigas quickly naturalized in the Puget Sound and began to spawn naturally there. With the establishment of local populations and the introduction of shellfish hatcheries, oyster seed importation from Japan ended in the 1970s. Local hatcheries are now the main source of oyster seed for farms in the Pacific Northwest.
Pacific oysters are large, averaging about five to six inches in length at maturity, although there are reports of oysters over a foot in length. They grow quickly, reaching market size as soon as 18 months, but can live up to 30 years. Shell shape varies depending on the location they are raised in, but the cup is generally deep, with large, rough folds. Because of the variation between Pacific oysters, they are commonly marketed by the name of the region or farm they are from.
Magallana gigas was previously classified as Crassostrea gigas, but the genus was split and Pacific species of Crassostrea were placed in their own genus in 2014.
Other farmed oysters
In addition to our native Olympia oysters and the Pacific oysters that are widely farmed in the Pacific Northwest, a few other specialty species are cultivated here in much smaller amounts. These are the European flat oyster, the Virginia oyster, and the Kumamoto oyster. None of these species have been naturalized in our region, unlike Magallana gigas.
Ostrea edulis, the European flat oyster, is now endangered in its native region. They were first introduced to the Pacific Northwest in the 1870s and were widely grown throughout Willapa Bay and the Puget Sound until the 1930s. Currently, they are farmed in Washington in very limited numbers. Ostrea edulis does not appear to naturalize in our region as it just about disappeared from the Pacific Northwest without human intervention.
European flat oysters range from Scandinavia to the Mediterranean and Black Seas. They are more rounded in shape and grow to about 1.5 to 4 inches in size. They are strong-tasting, with a tannic and slightly coppery flavor.
European flat oysters are sometimes referred to as Belon oysters, especially by growers in Maine, where they were introduced in the 1950s and locally naturalized. The name, however, is actually a protected designation for O. edulis oysters grown around the Belon River in Brittany, France. Regional differences matter with oysters, as they have different flavors depending on their provenance, so I personally feel that the name should be reserved for the French oysters.
Also known as the “Eastern oyster”, the Virginia oyster (Crassostrea virginica) is a species that was introduced from the eastern United States around the turn of the 20th century. The species was introduced to Willapa Bay around 1896, and kicked off the cultivation of Virginia oysters there as well as the Puget Sound and Samish Bay. Long-term, however, Virginia oysters fared poorly in the colder waters of the Pacific Northwest. They are much slower-growing in cold water, taking up to 4 years to reach market size, versus 18 months in Virginia. In addition, imported seed is required to maintain them. After a natural die-off in the late 1910s, the species was largely abandoned.
Today, though, they continue to have a limited presence in Washington. They seem to do especially well in the Totten Inlet at the southern end of the Puget Sound. Taylor Shellfish farms is the largest producer of Virginia oysters in Washington is Taylor Shellfish Farms.
C. virginica oysters are larger, reaching average sizes of 3 to 5 inches. They have a briny flavor that is milder than the flavor of Olympia oysters.
Magallana sikamea, the Kumamoto oyster, was introduced to Washington from Japan in 1947, after WWII ended and demand for Pacific oyster seeds rebounded. Kumamoto oysters grew in popularity quickly in the United States, and are now grown in Washington, Oregon, and California, where they gained much greater popularity than they did in Japan.
They are closely related to Pacific oysters (M. gigas), but they cannot naturalize in the Pacific Northwest because our waters are too cold. Coming from a warmer climate, Kumamoto oysters spawn later and in warmer waters than other oysters. As a result, they are of better quality later into summer.
The species is declining in its native region due to pollution and habitat destruction. In the Pacific Northwest, they also hybridized with Pacific oysters, so pure M. sikamea oysters became difficult to find. Efforts were taken to find purebred M. sikamea seeds and today, several growers, including Taylor Shellfish Farms, produce them in the Pacific Northwest.
Kumamoto oysters are less briny and considered fruitier than other oysters. They are slightly smaller than Pacific oysters, growing 2 to 3 inches in size, but with a deep cup and a good meat ratio.
