Ocean Quahog (Arctica islandica)

Ocean Quahog overview

The ocean quahog is a thick-shelled North Atlantic clam and the longest-lived non-colonial animal whose age has been reliably measured. Its rounded shell is covered by a dark brown to black outer skin, the periostracum, which earns it the trade name mahogany clam. It lives buried in sand and mud on the continental shelf, filtering plankton through short siphons, and grows extremely slowly in cold water. Like a tree, its shell lays down one growth line a year, which lets scientists age individual clams and use their shells as archives of past ocean climate. It is harvested commercially off the United States and Iceland.

How Long Do Ocean Quahogs Live?

Ocean quahogs commonly live 100–200 years, and the oldest one ever aged was 507 years old. That record clam, nicknamed Ming, was dredged off Iceland in 2006 and is an extreme outlier rather than a typical lifespan. Even so, clams over a century old are routine in commercial catches, and lifespans are shorter in warmer or brackish waters such as the Baltic.

How Much Does an Ocean Quahog Weigh?

An adult ocean quahog weighs roughly 100–300 g (3.5–10.5 oz) with its shell, though this is an approximate figure that varies with size and location. The heavy shell accounts for most of the weight, and the edible meat of a market-sized clam is only a few tens of grams.

How Long Is an Ocean Quahog?

Ocean quahog shells are typically 7–13 cm (2.8–5 in) long in adults. Growth is fast for the first couple of decades and then slows almost to a standstill, so a 100-year-old clam and a 300-year-old clam can be nearly the same size. Size alone is therefore a poor guide to age.

What Do Ocean Quahogs Eat?

Ocean quahogs are filter feeders that eat phytoplankton, mainly microscopic algae. Buried in the sediment with only their short siphons at the surface, they pump seawater across their gills, trap food particles in mucus and pass them to the mouth. They can also burrow deeper and shut down for days at a time without feeding.

Diet type: filter feeder. Microscopic algae and other phytoplankton, filtered from seawater drawn in through short siphons while the clam lies buried just below the surface of the seabed.

Where Do Ocean Quahogs Live?

Ocean quahogs live buried in sand and muddy sand on the continental shelf of the North Atlantic, mostly at depths of about 25–250 m (80–800 ft) off North America. In European waters they range from just below the shore to around 500 m. They need cold water and generally avoid areas where bottom temperatures exceed about 16 °C.

Are Ocean Quahogs Endangered?

The ocean quahog has not been evaluated for the IUCN Red List. United States stocks are assessed as not overfished, but the species is managed cautiously because it grows and replaces itself so slowly. In the North Sea it is listed by the OSPAR Convention as threatened or declining, largely because of damage from bottom trawling.

Not Evaluated

Ocean Quahog fun facts

• Ming, a 507-year-old ocean quahog, was born around 1499, during China's Ming dynasty, and was already old when Shakespeare was writing.
• Ming's age was first counted as about 405 years and revised to 507 in 2013, after researchers re-examined the growth lines using more precise methods.
• Scientists did not know Ming's age when it was collected; like the other clams in the sample, it was frozen on the research ship, which killed it.
• By matching growth-line patterns between shells, researchers have built year-by-year records of North Atlantic ocean conditions reaching back more than 1,000 years.
• Ocean quahogs are slow to mature as well as slow to age; many do not breed until they are around 7–13 years old, and some take longer.

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Ocean Quahog FAQ

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