Tresus capax is a species of saltwater clam, marine bivalvemollusk, common name the fat gaper, in the family Mactridae.[1] It also shares the common name horse clam with Tresus nuttallii a species which is similar in morphology and lifestyle. Both species are somewhat similar to the geoduck (Panopea generosa, which is in the family Hiatellidae), though smaller, with shells up to eight inches long (20cm), weight to 3–4lb (1.4–1.8kg).
The two species commonly known as horse clams inhabit the Pacific coast intertidal zones: the pacific gaper, T. 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. These clams are also commonly called gapers because their shells are flared around the siphon and do not completely close, rather like geoduck clams. Like geoducks, they are unable to completely retract the siphon within the shell, though less flagrantly as the siphon on Tresus species is not as large.
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.
Habitat and lifestyle
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 (30–41cm), 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 commensalpea crabs, Pinnixa faba, often a mating pair, which enter through the large siphon and live within the mantle cavity of the horse clam.[2][3] 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.[4]
Harvesting for food
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.
Identification is important. Best recipes vary with species. For resource sustainability, the Washington State Department of Fish and Wildlife sets size and bag limits for these clams. The Department of Health sometimes closes beaches for public health and safety. The Department of Health Marine Biotoxin web site has current information.
King County has a well-illustrated clam identification procedure .[5]
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.
Prehistorical exploitation
Early exploitation of horse clams is known by Native Americans 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 shells as a scoop implement. An unusually well decorated specimen was found at the present day town of Morro Bay during archaeological excavation.[6]
Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two shells of equal size connected by two adductor muscles and have a powerful burrowing foot. They live in both freshwater and marine environments; in salt water they prefer to burrow down into the mud and the turbidity of the water required varies with species and location; the greatest diversity of these is in North America.
The Pacific geoduck is a species of very large saltwater clam in the family Hiatellidae. The common name is derived from the Lushootseed name, gʷidəq.
A siphon is an anatomical structure which is part of the body of aquatic molluscs in three classes: Gastropoda, Bivalvia and Cephalopoda.
The Pacific razor clam, Siliqua patula, is a species of large marine bivalve mollusc in the family Pharidae.
The Atlantic surf clam, also called the bar clam, hen clam, skimmer or simply sea clam, is a very large, edible, saltwater clam or marine bivalve mollusk in the family Mactridae. It is commonly found in the western Atlantic Ocean, and is one of the most common species of bivalves found in the Northeast. Able to reach sizes between 7.9 and 8.9 inches in length, Atlantic surf clams are much larger than Spisula solida, which also resides in the eastern Atlantic coastal waters. Atlantic surf clams reproduce in late summer, when the water temperatures peak.
Lajonkairia lajonkairii is an edible species of saltwater clam in the family Veneridae, the Venus clams. Common names include Manila clam, Japanese littleneck clam, Japanese cockle, and Japanese carpet shell. In Japan, it is known as asari. In Korea, it is known as bajirak.
Pinnixa faba, known as the pea crab, mantle pea crab or large pea crab, is a pea crab which lives harmlessly within a large edible clam. This species is a symbiont of Tresus capax and Tresus nuttallii in its mature stage.
Leukoma staminea, commonly known as the Pacific littleneck clam, the littleneck clam, the rock cockle, the hardshell clam, the Tomales Bay cockle, the rock clam or the ribbed carpet shell, is a species of bivalve mollusc in the family Veneridae. This species of mollusc was exploited by early humans in North America; for example, the Chumash peoples of Central California harvested these clams in Morro Bay approximately 1,000 years ago, and the distinctive shells form middens near their settlements.
Panopea zelandica, commonly known as the deepwater clam or New Zealand geoduck, is a large species of marine bivalve mollusc in the Panopea (geoduck) genus of the family Hiatellidae. It is also sometimes called a king clam, or a gaper – in reference to the shell not being closed at either end.
Saxidomus nuttalli is a species of large edible saltwater clam, a marine bivalve mollusk in the family Veneridae, the venus clams. Common names include California butterclam and Washington clam.
Mya truncata, common name the blunt gaper or truncate softshell, is a species of edible saltwater clam, a marine bivalve mollusk in the family Myidae.
Dosewallips State Park is a public recreation area located where the Dosewallips River empties into Hood Canal in Jefferson County, Washington. The state park's 1,064 acres (431 ha) include both freshwater and saltwater shorelines. The park offers opportunities for picnicking, camping, hiking, boating, fishing, swimming, scuba diving, and shellfish harvesting.
Lutraria lutraria is a species of large marine bivalve mollusc in the family Mactridae. Its common names include the otter shell and the common otter shell. It occurs in coastal regions of the north east Atlantic Ocean where it lives buried in the sand.
Tresus is a genus of saltwater clams, marine bivalve mollusks in the family Mactridae. Many of them are known under the common name the horse clam or as species of gaper clam. They are similar to geoducks.
Tresus nuttallii, common name the Pacific gaper, is a species of saltwater clam, a marine bivalve mollusk in the family Mactridae. It also shares the common name horse clam with Tresus capax, a species which is similar in morphology and lifestyle. Both species are somewhat similar to the Geoduck, though smaller, with shells up to eight inches long (20 cm), weight to 3–4 lb (1.4–1.8 kg).
Geoduck aquaculture or geoduck farming is the practice of cultivating geoducks for human consumption. The geoduck is a large edible saltwater clam, a marine bivalve mollusk, that is native to the Pacific Northwest.
Saxidomus gigantea is a large, edible saltwater clam, a marine bivalve mollusk in the family Veneridae, the venus clams. It can be found along the western coast of North America, ranging from the Aleutian Islands to San Francisco Bay. Common names for this clam include butter clam, Washington clam, smooth Washington clam and money shell.
Nuttallia obscurata, the purple mahogany clam, dark mahogany clam, varnish clam or savory clam, is a species of saltwater clam, a marine bivalve mollusk in the family Psammobiidae. It was first described to science by Lovell Augustus Reeve, a British conchologist, in 1857.
Modiolus capax, common name fat horsemussel, is a species of "horse mussel", a marine bivalve mollusc in the family Mytilidae, the mussels. It was first described to science by American malacologist Timothy Abbott Conrad in 1837. The type specimen was collected in San Diego by Thomas Nuttall.
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