Clams
The word “clam” is a common name used to describe various edible aquatic mollusks with similar characteristics. Clams are bivalves, meaning they have hinged shells, like mussels, oysters, and scallops.
The mollusks we collectively call clams are from several different orders and families. Currently, the species in this article fall under four orders: Venerida, Cardiida, Adapedonta, and Myida. However, the current taxonomy of bivalves is undergoing revisions based on more recent phylogenetic research and may change in the future.
In the Pacific Northwest, we have a large diversity of bivalves and of species referred to as clams.
Species
Venus clams
Pacific littleneck clam (Leukoma staminea)
Manila clam (Ruditapes philippinarum)
Butter clam (Saxidomus giganteus)
Gaper clams
Pacific gaper clam (Tresus nuttallii)
Fat gaper clam (Tresus capax)
Razor clams
Pacific razor clam (Siliqua patula)
Sickle jackknife clam (Solen sicarius)
Geoducks
Pacific geoduck (Panopea generosa)
Cockles
Nuttall’s cockle (Clinocardium nuttallii)
Varnish and tellin clams
Purple varnish clam (Nuttalia obscurata)
Bodega tellin clam (Tellina bodegensis)
Macoma clams (Macoma nasuta, Macoma secta, and Macoma inquinata)
Softshell clams
Eastern softshell clam (Mya arenarea)
Piddocks
Rough piddock (Zirfaea pilsbryi)
Flat-tipped piddock (Penitella penita)
Freshwater clams
Freshwater bodies in the Pacific Northwest are home to an invasive clam species from Asia, the gold clam, Corbicula fluminea. Although edible, as with freshwater mussels, these clams should not be eaten - it is both prohibited and dangerous for your health. Unfortunately, freshwater clams in our region contain unsafely high levels of contaminants such as PCBs.
Venus clams
We have three species of edible Venus clams in the Pacific Northwest. Venus clams are in the family Veneridae, a large family of bivalves that includes many edible species around the world (including the famous quahog of the eastern United States).
We have three species here in the Pacific Northwest. Two are native, one was introduced in the 20th century. The two native species were important food sources for coastal indigenous people. All three Venus clam species are far more common in Washington than in Oregon, where the coast is less protected from the elements.
The Pacific littleneck clam, Leukoma staminea, is a small species of Venus clam in the family Veneridae. It is found from Alaska down to Baja California, but are most abundant north of Oregon.
The term “littleneck” is borrowed from the East Coast of the US, where Mercenaria mercenaria, the quahog or hard clam, is sold under different names based on its size. The “littleneck” is one of the smaller sizes. The name was borrowed and applied to Leukoma staminea, which grows on average to about 2 inches in size, though the species can sometimes reach 3 inches.
There is some aquaculture production of the native littleneck taking place in Washington. The species is not as fast-growing as the related Manila clam, but it is still a fast-growing species that is well-suited to cultivation. It currently only represents a very small percentage of farmed mollusks, but is very popular with recreational fishermen.
The Manila clam (Ruditapes philippinarum) is a related, non-native species of Venus clam that was introduced to the Pacific Northwest from Asia, where it has a broad distribution from India to northern Japan and Russia. They were introduced to western North America by the 1930s at latest, likely brought accidentally alongside oysters from Japan. The clams established themselves along the West Coast and are now found from British Columbia down to Baja California. The species was also introduced later to Europe, where it is widely established.
Today, the Manila clam is the most farmed species of clam in the world. Most of the production takes place in China, but it is also the major cultivated species in the Pacific Northwest. Manila clams are well-suited to aquaculture as they are relatively fast-growing, reaching a harvestable size in 2 to 3 years. They grow to about 2 inches in size, sometimes up to 3 inches.
Manila clams are easily mistaken for the native Pacific littleneck clam. They are sometimes called “Japanese littleneck clams”. The main distinguishing feature between the two species is that the shell of the Manila clam is smooth along its inner edge, whereas the native littleneck has ridges.
The butter clam (Saxidomus giganteus) is the largest species of Venus clam in our region. It ranges from Alaska to Northern California, but is rarely found south of Oregon. In the Pacific Northwest, they are most abundant in Washington and British Columbia, but they are commercially harvested in Oregon as well. Butter clams are not farmed.
Butter clams can reach large sizes up to 6 inches. They are on average about 4 inches in length.
Gaper clams
Gaper clams, also known as horse clams, are large clams in the family Mactridae. Although they are somewhat similar in appearance to geoduck clams, they are more closely related to Venus clams, which are also in the order Venerida.
Gaper clams are named for the shape of their shells. Their oversized siphons protude from their shells, which flare out to make room. Gaper clams are unable to fully retract their siphons.
These large clams can reach shell sizes of up to 10 or 11 inches. They are more commonly around 5 inches and weigh about a pound.
Here in the Pacific Northwest, we have two species of gaper clam, the Pacific gaper clam, Tresus nuttallii, and the fat gaper clam, Tresus capax. Both species are found from Alaska down to southern California. The fat gaper clam is more common in the northern portion of this range, whereas the Pacific gaper clam is more common in the southern portion and extends even further south into Baja California.
Gaper clams are harvested from the wild. Recently, they have become a more popular commercial fishing target in Oregon.
Razor clams
The common name “razor clam” refers to numerous different clams in the families Pharidae and Solenidae. There is disagreement if these two families are separate or not. All species are included in the order Adapedonta alongside geoducks.
Razor clams get their name for a couple of reasons. One is that the shells of many species resemble a straight-edge razor. Another reason is that you can cut yourself on their shells if attempting to grab them when digging them up. All razor clams are fast burrowers and will attempt to escape capture by digging down quickly.
Here in the Pacific Northwest, we have two species of razor clam.
Siliqua patula, the Pacific razor clam, is a highly-valued species of clam that can be found from Alaska to Central California. It is rare in the southern portion of its range.
This large clam can rarely grow to nearly 7 inches in length. It is more commonly about 3 to 4 inches long. Its shape is wider than other razor clam species, but still narrow and long. Its shell is easily broken. The clams are unable to fully close or retract their siphons.
Pacific razor clams have a long history of use in the Pacific Northwest by coastal indigenous people, as evidenced by their shells in middens. Their commercial sale by colonists dates back to the late 1800s. Most of the fishing for Pacific razor clams occurs from the northern Oregon coast up along the Washington coast. The majority of the commercial catch is taken in by the Quinault Indian Nation in Washington. The fishery is considered sustainable by the Seafood Watch program from the Monterey Bay Aquarium.
Solen sicarius, the sickle jackknife clam, is a species of long, narrow clam that grows to about 5 inches in length, but more often around 3.5 inches.
Sickle jackknife clams are not often collected but they are edible and considered tasty. Similar clams in the genera Ensis and Solen are found elsewhere in the world and these species are eaten in their respective regions.
Many sources consider Solen sicarius to be uncommon, but I’ve had trouble determining if this is actually the case. Jackknife clams are strong and fast diggers that are more difficult to catch than other clam species. As a result, there is a distinct possibility that their abundance may have been underestimated. I did find a couple of reports from the 1960s that suggested that might be the case, but it’s hard to say.
Geoducks
Panopea generosa, the Pacific geoduck (pronounced “gooey-duck”), is the largest and deepest burrowing clam in the world. The species is in the rockborer family, Hiatellidae, in the order Adapedonta.
This clam is well-known for the phallic appearance of its siphon. The shell grows to about 7 inches on average. The large siphon, on the other hand, can grow to over 3 feet in length. The clams weigh on average about 2.5 pounds.
The name “geoduck” comes from the Lushootseed name for the clam, “gwidəq”. Lushootseed is a Salish language from the Puget Sound area, where geoducks are plentiful. The meaning of the name is disputed, thought to either refer to the penis-like appearance of the clam or to mean “dig deep”.
Pacific geoducks are found from Alaska down to Baja California, but are considered uncommon in Oregon and California. Geoducks are found in high densities in the Puget Sound region, which supports a major commercial fishery. The primary market for geoducks is in Asia, where the clams fetch a high price (and where some consider it an aphrodisiac, simply due to its shape). Roughly 90% of the geoducks harvested in Washington are shipped to China.
The fishery for geoducks is, in fact, fairly recent. A fishery was established in 1970 in Washington and soon after in British Columbia. Although recreational digging for geoducks takes place in intertidal zones, commercial harvesting is done in deeper waters by divers. About two thirds of the commercial harvest is collected this way. The remainder comes from aquaculture operations.
Aquaculture practices
Geoduck farming was pioneered in Washington in the late 1980s. Geoduck farming is centered around the southern Puget Sound and is considered a sustainable practice by the Seafood Watch program.
Plastic PVC tubes are used to protect immature geoducks from predation. Once they are large enough, the tubes are removed. The geoducks are harvested when they reach a large enough size, after about 5 to 7 years. Geoducks are long-lived: the oldest specimen was estimated to be 168 years old. However, they grow fastest in the first three years, and growth slows down significantly after 10 years.
The farming methods developed in Washington were also adopted in British Columbia, but modified and use to reseed subtidal beds with more geoducks, rather than farm in intertidal zones.
Cockles
Cockles are clams in the family Cardiidae that have symmetrical, ribbed shells. They are heart-shaped when viewed from their profile. Cockles are found along sandy and muddy shores buried close to the surface (or not at all), and are commonly collected with a rake.
Clinocardium nuttallii, or Nuttall’s cockle, is our local native species of cockle that is found from northern Japan, to Alaska and down into southern California. It is common throughout its range but not usually found in very high concentrations. C. nuttallii is a large species, reaching average sizes of 3 inches. They can sometimes grow to 4 or even 5 inches.
Cockles are not a major fishery in our region but they are harvested and sold on a smaller scale. Historically, they have been the main targeted species in Oregon in terms of total biomass.
Varnish and tellin clams
Sunset clams and tellin clams are, like cockles, in the order Cardiida, but are grouped together in the superfamily Tellinoidea. Our native tellin and macoma clams are not commonly harvested, but a recent non-native species, the varnish clam, has gained some culinary importance in the Pacific Northwest.
Varnish clams
The purple varnish clam, Nuttalia obscurata, is a species of that was introduced to the Pacific Northwest from Asia. These clams are in the family Psammobiidae, which is closely related to tellin and macoma clams. Recently, there have been attempts to market the clams under the new name “savory clams”. I personally prefer the original name, which refers to the varnish-like brown coating on the outside of the shell (known as a “periostracum”).
The purple varnish clam is native to eastern Asia, from China and Japan up to Russia. The species is though to have been brought to British Columbia in the late 1980s or early 1990s in ships’ ballast water. From there, it spread to Washington and Oregon, and are now found from the Strait of Georgia in British Columbia down to Coos Bay, Oregon. They are most abundant where freshwater meets the ocean.
Varnish clams grow up to 3 inches at most, but are more commonly 1 to 2 inches. The shell is purple on the inside and can be sharp on the edges. It has two separate siphons rather than a single combined one.
Varnish clams are eaten locally in their native range but are not highly sought after. Currently, in the Pacific Northwest, there are recreational fisheries established everywhere they are found. At present, the commercial market for varnish clams is developing. They are are sold out of British Columbia, where they are primarily collected as bycatch from other clam fisheries. They are not farmed.
Tellin clams
Tellin clams and macoma clams are closely related species in the Tellinidae family. The common name tellin is often applied to both types of clams. Neither are not commonly collected in the Pacific Northwest, but they are all edible. Most are small and not considered worth the trouble of harvesting. There are, however, a handful of species that are large enough to mention here.
A similar, related species, Donax trunculus, is commonly eaten in Europe. The clam has many different common names in various languages, including “wedge shell” in England, “telline” or “flion” in France, “coquina” in Spain, “tellina” or “arsella” in Italy, and “conquilhas” in Portugal. The wedge clam is cooked in the shell like other small clam species.
Megangulus bodegensis, the bodega tellin, can be found from southern Alaska down to northern Mexico. It was formerly known as Tellina bodegensis.
A 1958 publication on clams in Oregon stated that these clams were found in large enough quantities to harvest in Coos Bay, Yaquina Bay, and Tillamook Bay (at least certain years). The report also stated that the average clam size was about 2.5 inches. Other sources say the clams are slightly smaller than that.
Macoma clams are a group of clams with at least a dozen species along the Pacific coast of North America. Macomas are closely related to tellins. Those that are large enough to be of interest include:
the bent-nose macoma (Macoma nasuta). These are about 2 inches in size, sometimes up to 4 inches. The bent-nose macoma, which gets its name from the bent tip of its shell, was once an important food source for coastal indigenous people, as evidenced by the presence of shells in middens. It was also apparently eaten by Chinese immigrants around San Francisco, though I have not been able to confirm this statement.
Several of the studies I looked at state that these clams are highly abundant in muddy coastal areas, at least in Northern California and the Puget Sound. It seems likely that this would be true along their entire range.
the white sand macoma (Macoma secta). Commonly around 2 inches big, sometimes up to 4 inches.
the stained macoma (Macoma inquinata). The smallest of these three species, about 1 to 1.5 inches on average.
Softshell clams
The eastern softshell clam, Mya arenarea, is a species of clam in the family Myidae that was introduced from the eastern United States, where it is commonly known as a “steamer”. Here on the West Coast, we call it a “softshell”, referring to its brittle, easily broken shell.
Softshell clams are about 2 to 4 inches in length, with dark siphon tips that must be removed before eating. The clams are found in less saline waters, often higher upriver than other species.
The softshell clam was introduced to the San Francisco Bay from the eastern United States in the 1870s when attempts were being made to establish a Virginia oyster fishery along the West Coast. From there, they were intentionally introduced elsewhere in California as well as in the Oregon, Washington, and British Columbia. Today, the softshell clam is found from Alaska to northern California. It was not successfully introduced south of San Francisco.
It is thought that Mya arenarea originated in the northern Pacific Ocean during the Mioecene period, but went extinct throughout most of its range during the last ice age. In an odd twist, humans have now reintroduced the species to western North America.
In the Pacific Northwest, softshell clams are mostly harvested recreationally from wild stocks and are uncommon as a commercially sold product. Along their native range in the eastern United States, they are also cultivated for sale, but such practices have not been established here.
Piddock clams
Piddocks are a group of clams in the Pholadidae family. Like the softshell clam (which is also in the order Miyda), piddocks have brittle shells. The clams gain protection by boring into rock or other softer substrates which they accomplish using specialized serrations on the lower end of their shells. Their burrowing action leaves holes throughout the rocks and clay they inhabit.
The rough piddock, Zirfaea pilsbryi, is found from Alaska to Baja California. It grows from about 3 up to 6 inches in length. One side of the clam has ridges on it for burrowing. The other side of the shell flares open, from which the clam’s oversized siphon protrudes.
Rough piddocks were apparently once eaten but are no longer sought after. Piddocks, which were often called “rock oysters”, did appear on menus in Oregon in the early 20th century. Extracting the clams requires special equipment such as a sledge or pickaxe to destroy the surrounding rock. Rough piddocks do not seem to have a reputation for having a better flavor than other clams, which likely explains the lack of interest in them.
The flat-tipped piddock, Penitella penita, is another, smaller species, that was also sometimes collected. It is about half the size of the rough piddock and is found along a similar geographic range.
Cooking with clams
Small clams are commonly steamed whole and then eaten from the shell, similarly to mussels.
Large clams are broken down and cleaned. The various parts of the clam may be prepared separately or or ground together for use in dishes such as chowder or clam cakes. Cleaned meat can be battered and fried. Some species, such as cockles, razor clams, and geoducks, may be tenderized with a mallet before cooking.
Clams can also be eaten raw. In the case of the geoduck, the siphon is commonly sliced thin and eaten raw.
Purging clams
Commercially supplied clams are generally purged before sale, but not always. Recreationally harvested clams, on the other hand, always need to be purged before cooking, to remove any unpleasant sand, mud, or other grit from them.
To purge clams, they are placed in cold, heavily-salted, unchlorinated water or in seawater for a certain amount of time. Freshwater will kill clams. The idea is to recreated the clam’s environment as best as possible, but without sand or mud in the water, so that the clams can cycle the water through them and expel any particles they contain.
Some species, such as tellin and macoma clams, require longer purging than others. However, clams can suffocate from a lack of dissolved oxygen in the water, so if the clams are being purged for longer than a day, it is important to replace the water with new seawater or salted water, or to mechanically aerate it.
Pea crabs
Pinnotheres pisum, the pea crab, is a very small species of crab that is often found inside clams and other mollusks. Although considered a parasite of the mollusks, they are harmless to humans. They can be removed from clams, but these soft-bodied crabs are also perfectly edible, and even considered desirable by some, who enjoy their flavor.
Safety precautions
As with all other shellfish, clams are susceptible to accumulating biotoxins from algae in the water. Commercially farmed shellfish is commonly tested for toxins. Local governments monitor wild shellfish and issue warnings when algae levels are unsafe. The risk of unsafe levels is higher in summer, when the weather is warmer, but can still occurs at other times of the year.
Arsenic in wild clams
Softshell clams and gaper clams were found by Oregon authorities to have higher-than-expected levels of inorganic arsenic in them. The arsenic in the clams is thought to accumulate from naturally occurring arsenic in our local soil. Levels were found to be highest in the northern half of the Oregon coast.
The Oregon Health Authority has issued an advisory with recommended consumption limits for softshell and gaper clams. The arsenic levels are mostly concentrated in the skin surrounding the siphons of these clams, so the skin should not be eaten.
