Bay Scallop


Argopecten irradian

Color: Exterior shell color range from dab gray to yellow or reddish brown. Interior is white, often purplish near the hinge.

Size: 3 inches in diameter

Habitat: Subtidal zone, eelgrass beds, sandy and muddy bottoms, offshore in shallow to moderately deep water, such as bays and harbors.                                      

 Seasonal Appearance: All year

 Sensitivity to Human Action      





Distinguishing Features and Behaviors:

     The bay scallop is one of the few filter-feeding bivalves that do not live buried in the sand or attached to rocks. Instead they settle and move freely along the bottom sediment surface. Unlike most bivalves, which are oblong or oval, the corrugated shell of the bay scallop is almost perfectly circular. The scallop has a strong hinge muscle within the shell but does not have a foot for digging or a siphon for water intake.

     Along the edge, or mantle, of bay scallop shells are 30 to 40 bright blue eyes. Each eye has a lens, retina, cornea, and optic nerve, enabling it to see movements or shadows and detect predators. Along the edge of the mantle are tentacles containing cells sensitive to chemical information in the water. These cells help the scallop react to its environment. When a scallop senses danger, such as a sea star, it swims away by clapping the two sides of its shell together vigorously. This clapping movement forcibly ejects water from the mantle cavity through an exit near the hinge, propelling the bay scallop in a bouncing motion.

     Scallops reach maturity when they are a year old, and they spawn in the summer. They grow quickly, rarely living past three years of age. When bay scallops are young, they attach themselves to objects such as eelgrass by means of a byssal thread. This helps them avoid bottom-feeding predators. As the scallops grow, they drop to the sediment surface in the vicinity of eelgrass beds and move on to tidal flats to feed at high tide.

Relationship to People:

     The abductor muscle of the bay scallop makes excellent food, and scallops are harvested in the Bay using dredges, nets, and rakes. In the 1880’s populations were so healthy that Rhode Island was a top supplier of scallops to New York. In the 1930’s, many of the eelgrass beds in Narragansett Bay began to die off as a result of pollution, leading to a severe reduction in the bay scallop population.

     Populations have continued to decline in the Bay in recent years. Previously, one of the richest areas for scalloping in Rhode Island was GreenwichBay. Today, it has no significant scallop population as a result of eelgrass degradation and loss caused by shoreline development and pollution.

     Efforts are under way by state environmental groups to restore scallop population in areas where they were historically found in the Bay.