Sea Scallop Factsheets

What's a scallop?

Sea scallops, or Placopecten magellanicus, are also commonly known as giant scallops, Atlantic deep sea scallops, smooth scallops, and ocean scallops. The sea scallop is a bivalve, which means that it is an organism that is encased in two shells (valves). The shells of the scallops are very iconic; they are usually a bright color (orange in the case of the sea scallop), and are unique among bivalves because they have long ridges that run across the outer surface of the shell. Because the radiating ribs on a scallop shell resemble a Roman comb, it was given the genus name Placopecten, which translates from Latin to mean "appeasing comb".

Where do scallops live?

Sea scallops can be found on seafloor bed types ranging from mud, sand, and gravel to the remains of other organisms, like broken shells. Sea scallops typically prefer coarser sediment types because during their larval stage they look for hard surfaces to attach to.

Can scallops swim?

Yes they can! Scallops can make a clapping motion with their shell to swim away from predators such as crabs, sea stars, and some fish. Scallops are able to detect predators with their eyes and by sensing changes in chemistry of the surrounding seawater. Each black dot on the white mantle of the scallop is an eye, and each scallop has as many as 100 eyes.

Predators and Prey

Sea scallops are filter feeders. They eat phytoplankton and zooplankton that gets filtered through its gills where it is trapped in mucus.

Sea scallop predators include crabs, lobsters, sea stars, and some fish.

Why are scallops harvested?

Because they're delicious! The part of the scallop that you eat is the adductor muscle. This is the muscle that the scallop expands and contracts to open and close its shell. Each year fishing vessels like the Christian and Alexa, set sail off of the North Atlantic coast in order to catch sea scallops. Once they are a few miles off the coast, they drop dredges that they tow along the seafloor, which can catch hundreds of scallops at a time. The contents of the dredges will be emptied onto the deck of the ship where the scallops are sorted and shucked (removing the adductor muscle from the shell). Each year, between 15,000 and 25,000 metric tons of sea scallop meat are fished from Mid-Atlantic waters.

The northwest Atlantic scallop grounds have been important to the United States and Canada for over a hundred years. In 2010 alone, sea scallop landings accounted for $450 million dollars. The area that you're exploring in SubseaObservers is the Mid-Atlantic Bight (the shallow portion of the continental shelf that extends from Cape Hatteras, NC to Cape Cod, MA), which has been commercially significant since the 1920s when scallop grounds were first discovered off of Long Island. Since that time, sea scallops have continued to be harvested from this region and have been overfished periodically.

How are scallop stocks assessed?

To maintain the health of the scallop fishery, the National Marine Fisheries Service (NMFS) conducts yearly stock assessments to evaluate the scallop population and to set catch limits for the following year. The stock assessments are typically performed by ships dragging dredges along the seafloor that capture scallops so that they can be manually counted and sized.

Researchers at the University of Delaware have teamed up with Dr. William Phoel and the fishing vessel Christian and Alexa (co-captained by Arthur Ochse and Kenneth Ochse) to develop a method of estimating the Mid-Atlantic Bight sea scallop population and classify their sizes using seafloor photographs, rather than the current method of dredging the seafloor for scallop samples.

The images used in SubseaObservers were collected using an Autonomous Underwater Vehicle (AUV), which allows for the observation of the scallops in their natural habitat. By contributing to SubseaObservers, you're helping to determine the health and population of the scallop fishery, in addition to providing information about the distribution of scallops within the fishery, all without disturbing the natural habitat of the scallops or other aquatic life.

For more information about AUVs, check out the Learn more about AUVs section.

How big do scallops get?

Shell height is measured from the middle of the hinge to the front tip where the shell first opens when pulled apart, and some sea scallops have been recorded to grow over 8 inches (203.2 milimeters) in length during its lifetime. The sea scallop first forms its shell during its planktonic larval stage, and this shell continues to grow for the rest of its life. The size of the scallop shell is used to determine if a scallop can be harvested or if it must be released back to the ocean. If the shell height is greater than 4 inches (101.6 milimeters), the scallop can be kept and sold.

Just like counting the rings of a tree to determine its age, the age of the scallop can be determined by counting the number of major rings on the outside of the scallop shell. Sea scallops have been know to have lifetimes up to 29 years!

Meet the scallop fishermen
Scallop Factsheets

What's a scallop?

How big do scallops get?

Where do scallops live?

Can scallops swim?

Predators and Prey

Why are they harvested?

Meet the scallop fishermen

How are stocks assessed?

Learn more about scallops