Facts about clams- lifecycle, habitat, what they eat, types of clams harvested etc
Shellfish are bivalve mollusk, which have laterally compressed bodies enclosed by a shell in two hinged parts. Clams, oysters, mussels, and scallops are all types of shellfish.
Clams live in the mud, sand and gravel intertidal area found along coastal regions.
Species harvested in Maine:
Two kinds of clams are harvested in Maine: soft shell and hard shell. Both are harvested year round, with the peak season in the summer months. Soft shell clams (Mya arenaria), aka steamers
Soft shell clams live in the mud, sand, and gravel intertidal areas. It takes about three to four years for a clam to grow to market size, which is two inches.
Today the harvest averages around 10 million pounds per year, and the value of soft shell clams has increased over time, making soft shell clams Maine’s third most valuable fishery.
Hard Shell Clams
Maine Ocean quahog aka mahogany clam Arctica islandica
Mahogany clams, or Maine Ocean Quahogs, are small hard shell clams that are harvested from Maine’s coastal waters. They derive their name from their rich mahogany color. The fishery is divided into a federal (3-200 miles offshore) and state fishery. Though small-scale, the fishery that takes place in federal waters is part of the Mid Atlantic’s Surf Clam and Ocean Quahog Individual Fishing Quota (IFQ) program. Though part of the IFQ program, Maine is given a separate state quota (100,000 bushels) that is fished competitively. The state ocean quahog fishery is open access but the catch is counted towards the federal quota (Amendment 10 to the Surfclam and Ocean Quahog Fishery Management Plan- Mid Atlantic Fisheries Management Council). Boats in the Maine fishery are small (35-45 ft) and are only permitted to use dry (non-hydraulic) dredges with a cutter bar that is no more than 36 inches. Historically the bulk of ocean quahog fishing activity in Maine has taken place on two large quahog beds near the town of Addison and Great Wass Island- about a 60 square nautical mile radius (Draft Ocean Quahog Assessment Update 2013). Mahogany clams are typically harvested at about 38-64 mm shell length.
Atlantic Surf Clam or Hen Clam Spisula solidissima
The Atlantic Surf Clam, aka Hen Clam, are very large and fast growing clams which can grow to 8 inches or more, and weigh over a pound. Similar to merceneria mercenaria, these clams are also called chowder clams. They live burrowed into the sand on the continental shelf and beneath the turbulent waves of the surf breaker zone. Maine has historically been at the northern edge of their geographic range, but with warming waters associated with climate change we may see more and more atlantic surf clams in Maine waters.
Quahog, Cherrystone, Topnecks, Littleneck, Countnecks Mercenaria mercenaria
Mercenaria mercenaria are referred by different names depending on their size. In the order of largest to smaller, these clams are called: Quahogs (Chowderhogs), Cherrystones, Topnecks, Littlenecks, and Countnecks. This species is found in the sand and mud habitats of the intertidal and sheltered subtidal hard mud and sand.
Like the atlantic surf clam, Maine has been at the northern fringe of Mercenaria mercenaria’s habitat range. Now that rising ocean tempretures have stopped these clams from being killed by ice in the winter, their range may be expected to expand throughout Maine’s intertidal waters. In fact, wild clammers have been observing an increase in these clams in Maine’s intertidal regions recently.
Clams feed by drawing in water through a siphon. The food is filtered out of the water by the gills and swept into the mouth by a layer of mucus. The water is then expelled from the animal through an ex-current siphon. Since clams are filter feeders, the presence of clams and other bivalves in the water actually improves water quality.
The health and stability of Maine clam populations are threatened by pollution and poor water quality caused by agricultural and residential runoff, increased shoreside development, and aging infrastructure. Additionally, clams are threatened by the invasive green crab, whose populations have exploded in recent years due to warming temperatures caused by climate change.