Maryland Fish Facts

Shellfish - Hard Shell Clam
Shellfish - Hard Shell Clam


Shellfish - Hard Shell Clam
Mercenaria mercenaria
(A.K.A. Northern quahog, Hard clam, Littleneck, Cherrystone, Chowder)
Key Distinguishing Markings:
  • Shell heavy, thick and strong.
  • Outside color grayish, sometimes tinged with brown or tan.
  • Shell sculpture of numerous concentric growth lines with smooth area near middle of shell.
  • Interior white, usually with a splotch of purple stain.
  • Interior margin of shell with crenulations (fine teeth).​

Distribution:
  • Hard-shell clams are found along the coast from the Gulf of St. Lawrence to Texas.
  • In Maryland, they occur in higher salinity waters (>15 ppt), especially in the Atlantic coastal bays, with smaller populations in southern Tangier and Pocomoke Sounds and lower Chesapeake Bay.​

Size:
  • Adults can grow as large as 125 mm (5 in)
  • Sexual maturity is reached at a shell length of 32-38 mm (1 3/8-1 1/2 in)
  • Various size groups have distinct common names:
      • Button: <1 7/8 in
      • Littleneck: 1 7/8 – 2 1/8 in
      • Topneck: 2 1/8 – 2 3/8 in
      • Cherrystone: 2 3/8 – 3 1/8 in
      • >Chowder: >3 1/8 in​

Habitat:
  • Hard-shell clams occur mainly in bays and estuaries along the coast, from the intertidal zone to depths of about 18 m (60 ft).
  • They are found in a variety of substrates, but prefer sandy bottoms, especially with shell.
      • The shell protects the more vulnerable smaller clams from predators.
  • The clams live buried only about 1 – 2 in below the bay bottom.​

Spawning:

Spawning and Development:

  • Hard-shell clams are capable of spawning from May-October, when water temperatures rise above about 23°C (73°F).
  • The gametes are released into the water column, where fertilization occurs.
      • Females can release as many as 16-24 million eggs per spawn, but this is highly variable; the average is about 7 million eggs per spawn.
  • After fertilization, shelled larvae (sing. larva) develop. They swim in the water column for about 2 to 3 weeks, feeding on planktonic algae.
  • Water currents distribute the larvae around the estuary.
      • Mortality is very high during this stage of their life history.
  • As the larvae get older, they begin to resemble little clams. Eventually, they develop a foot which they use to test the substrate for a suitable place to settle.
  • After they find a good location, and if they large enough (~ 0.2 mm), the larvae undergo metamorphosis, when they change into the juvenile stage by attaching to the substrate with thin byssal threads (like a spider spinning a web, only simpler), losing their swimming organs, and developing gills and siphons.
  • Eventually, at a size of about 7-9 mm, the juvenile clam loses its byssal threads and digs into the bottom.
  • Although clams have a foot for digging, they remain in the same general location for the rest of their lives.
  • Hard-shell clams in Maryland reach the legal harvesting size in about 3 years.​

Fishing Tips:

Clamming Tips:

  • Clamming is a popular recreational activity in the coastal bays behind Ocean City and Assateague Island.
  • Clams can be caught by raking or treading (feeling for the clams with your foot), especially in sandier areas.
  • No license is required for recreational clamming but there are restrictions on the daily take and the minimum size that can be kept.
  • For current regulations (both commercial & recreational), see Maryland's updated regulation page.

Fun Fact:
  • Hard-shell clams can live over 40 years.
  • This species is enjoyed in a variety of culinary ways, such as chowders, clam bakes, and on the half shell. Clam chowder may have been the first American soup.
  • People aren't the only species that eats hard-shell clams. A wide variety of predators, including snails, crabs, shrimp, starfish, fish, and birds consume clams.
      • Herring gulls will carry clams into the air, and then drop them on hard surfaces such as rocks and parking lots to break their shells, allowing access to the meat.
  • Aside from food, Native Americans prized the shells of hard-shell clams for making wampum beads. Wampum was used as a form of money, hence the Latin name Mercenaria for this species.
      • The shells were also used for making tools such as scrapers, knives, spoons, and hoes.
  • The hard-shell clam population in the coastal bays has only existed since the mid-1930's. A hurricane in 1933 created the Ocean City Inlet, which allowed the ocean to flood into the then-brackish bays, raising salinities and providing a suitable environment for the clams.​

Family: Veneridae
Order: Veneroida
Class: Bivalvia

Phylum: Mollusca

For more information on hard-shell clams, please contact Mitchell Tarnowski.​