Horse clam
Encyclopedia
The horse clam are related to the Geoduck
, though smaller, with shells up to eight inches long (20 cm), weight to 3–4 lb (1.4–1.8 kg). Two similar species of horse clams inhabit the Pacific coast intertidal zone
s: the pacific gaper, Tresus nuttallii, more abundant south to California; and the fat gaper, T. capax, more abundant north to Alaska. Both have oval and chalky-white or yellow shells with patches of brown periostracum (leather-like skin) on the shell. Horse clams are called gapers because their shells are flared around the siphon and do not completely close, rather like geoducks. Like geoducks, they are unable to completely retract the siphon within the shell, though less flagrantly.
Their habitat is the lower intertidal zones on out to waters as deep as 50–60 feet (13-15 m). They prefer sand, mud, and gravel substrates
, normally burying themselves 12–16 inches (30–41 cm), so they are much easier to dig than geoducks. Their preferred substrates are also preferred by butter and littleneck clams, so horse clams are often taken incidentally in commercial harvesting.
Horse clams often have a relationship with small commensal
pea crab
s, often a mating pair, which live within the mantle cavity of the horse clam. The crabs are easily seen and in no way affect the clam as food. The meat is good and makes excellent chowder. They tend to be ignored by sport diggers in Washington but not in Oregon.
Horse clams are broadcast spawners like geoducks; T. nuttalii spawns in summer and T. capax in winter.
Appreciated by pre-contact local Native Americans for their size, abundance, and relatively easy capture, they are less sought today than geoducks, which have gained a marketing cachet.
King County has a well-illustrated clam identification procedure http://dnr.metrokc.gov/wlr/waterres/beaches/clam/clamid.htm.
Some clammers find horse clams are not as tasty as others, so it's not unusual during clamming season to find horse clams left behind on the beach. The shells are more fragile than they might appear, so it is critical that they not be damaged when first digging if they are not kept. The clams will soon die if abandoned. The adults are unable to rebury themselves—they need the pressure of their surroundings to remain intact and maneuver. They can't hold their two big valves together, protecting their soft tissues. Responsible diggers carefully rebury them to about the depth at which the clams were found. Diggers should fill all of the holes that they dig.
on the Pacific Ocean
coast of California
. For example, archaeological recovery from Chumash sites in San Luis Obispo County has revealed use of Horse clam shell as a scoop implement. An unusually well decorated specimen was found at the present day town of Morro Bay during archaeological excavation.
Geoduck
The geoduck , Panopea generosa, is a species of very large saltwater clam, a marine bivalve mollusk in the family Hiatellidae.The shell of this clam is large, about to over in length, but the very long siphons make the clam itself very much longer than this: the "neck" or siphons alone can be ...
, though smaller, with shells up to eight inches long (20 cm), weight to 3–4 lb (1.4–1.8 kg). Two similar species of horse clams inhabit the Pacific coast intertidal zone
Intertidal zone
The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...
s: the pacific gaper, Tresus nuttallii, more abundant south to California; and the fat gaper, T. capax, more abundant north to Alaska. Both have oval and chalky-white or yellow shells with patches of brown periostracum (leather-like skin) on the shell. Horse clams are called gapers because their shells are flared around the siphon and do not completely close, rather like geoducks. Like geoducks, they are unable to completely retract the siphon within the shell, though less flagrantly.
Identification
An easy way to tell the two species apart is that T. nuttallii usually has relatively longer, narrower shells (longer compared to height) and larger siphonal plates (horny plates found at the tip of the siphon, often with a little algae or barnacles garden). Hence T. capax is the fat gaper.Their habitat is the lower intertidal zones on out to waters as deep as 50–60 feet (13-15 m). They prefer sand, mud, and gravel substrates
Substrate (marine biology)
Stream substrate is the material that rests at the bottom of a stream. There are several classification guides. One is:*Mud – silt and clay.*Sand – Particles between 0.06 and 2 mm in diameter.*Granule – Between 2 and 4 mm in diameter....
, normally burying themselves 12–16 inches (30–41 cm), so they are much easier to dig than geoducks. Their preferred substrates are also preferred by butter and littleneck clams, so horse clams are often taken incidentally in commercial harvesting.
Horse clams often have a relationship with small commensal
Commensalism
In ecology, commensalism is a class of relationship between two organisms where one organism benefits but the other is neutral...
pea crab
Pea crab
The New Zealand pea crab, Pinnotheres novaezelandiae, is a small, parasitic crab that lives most commonly inside New Zealand green-lipped mussels. Adult females are about the size and shape of a pea, while adult males are smaller and flatter. Adult New Zealand pea crabs are completely reliant on...
s, often a mating pair, which live within the mantle cavity of the horse clam. The crabs are easily seen and in no way affect the clam as food. The meat is good and makes excellent chowder. They tend to be ignored by sport diggers in Washington but not in Oregon.
Horse clams are broadcast spawners like geoducks; T. nuttalii spawns in summer and T. capax in winter.
Appreciated by pre-contact local Native Americans for their size, abundance, and relatively easy capture, they are less sought today than geoducks, which have gained a marketing cachet.
Harvesting
Identification is important. Best recipes vary with species. For resource sustainability, the Washington State Department of Fish and Wildlife http://wdfw.wa.gov/ sets size and bag limits for clams. The Department of Health sometimes closes beaches for public health and safety. The Department of Health Marine Biotoxin web site http://www.doh.wa.gov/ehp/sf/biotoxin.htm has current information.King County has a well-illustrated clam identification procedure http://dnr.metrokc.gov/wlr/waterres/beaches/clam/clamid.htm.
Some clammers find horse clams are not as tasty as others, so it's not unusual during clamming season to find horse clams left behind on the beach. The shells are more fragile than they might appear, so it is critical that they not be damaged when first digging if they are not kept. The clams will soon die if abandoned. The adults are unable to rebury themselves—they need the pressure of their surroundings to remain intact and maneuver. They can't hold their two big valves together, protecting their soft tissues. Responsible diggers carefully rebury them to about the depth at which the clams were found. Diggers should fill all of the holes that they dig.
Prehistorical exploitation
Early exploitation of the Horse clam is known by Native AmericansNative Americans in the United States
Native Americans in the United States are the indigenous peoples in North America within the boundaries of the present-day continental United States, parts of Alaska, and the island state of Hawaii. They are composed of numerous, distinct tribes, states, and ethnic groups, many of which survive as...
on the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
coast of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. For example, archaeological recovery from Chumash sites in San Luis Obispo County has revealed use of Horse clam shell as a scoop implement. An unusually well decorated specimen was found at the present day town of Morro Bay during archaeological excavation.
Further reading
- Abbreviated edition of the clam identification key by the Washington State Department of Fish and Wildlife at the King County Department of Natural Resources
- Science: Geoduck and Horseclam Biology, an overview by Underwater Harvesters Association, British Columbia, developers of underwater farming.