Maryland Fish Facts

Shellfish - Bay Scallop
Shellfish - Bay Scallop


Shellfish - Bay Scallop
Argopecten irradians

Key Distinguishing Markings:
  • Shell lightweight, thin, but strong.
  • 13 to 22 symmetrically radial ribs originating from central point (umbo) of shell.
  • The marginal wings or ears at the umbo are slightly different in size and shape.
  • Bottom valve more convex than top valve.
  • Color highly variable in this species:
    • Top (left) valve – drab; dark grey, black, or brown; occasionally with yellow, orange, or red highlights; ribs sometimes mottled or concentrically banded.
    • Bottom (right) valve – usually lighter in color than top valve, sometimes pale yellow or white.​

Distribution:
  • Bay scallops are primarily found from Massachusetts to Texas.
  • In Maryland, they only occur in the coastal bays behind Ocean City and Assateague Island.​

Size:
  • Adults can grow as large as 90 mm (3 ½ in).
  • Scallops reach sexual maturity at about 55 mm (2 ¼ in), although age actually determines this.​

Habitat:
  • Bay scallops inhabit the higher salinity (>15-20 ppt) shallows of bays and estuaries along the coast.
  • This species is intimately associated with eelgrass beds.
  • When a blight wiped out the grass beds in the 1930's, scallop populations plummeted and completely disappeared in some areas.
  • Young scallops attach to blades of eelgrass with thin byssal threads.
  • By suspending themselves above the substrate, they are removed from suffocating silt and bottom-marauding predators such as crabs.
  • Adult scallops live on the bottom, unlike many other bivalves such as clams which live buried in the sediment.
  • Because scallops do not burrow into the bay bottom, adults only have a non-functional foot and do not have siphons.
  • They can also be found occasionally on shelly areas such as the remnant oyster shell bars in Chincoteague Bay.​

Spawning:
  • Scallops are hermaphrodites, simultaneously having both male and female sex organs.
  • Spawning in Maryland occurs during May/June, with a second spawning in September.
  • Eggs are released into the water column, where they are fertilized.
  • During its spawning period, a one-year old scallop produces an average of 16 million eggs.
  • The fertilized eggs develop into swimming larvae, complete with tiny shells.
  • Water currents distribute the larvae around the estuary. Mortality is very high during this stage of their life history.
  • After about 2 weeks, the larvae drop out of the water column and change into juvenile scallops, a process called metamorphosis.
  • During metamorphosis, a foot and gills develop, the swimming organ disappears, and the tiny scallops attach to seagrasses or other objects.
  • The foot, along with byssal threads, allows the juveniles to crawl up the grass blades.
  • The juveniles will remain attached until they reach a size of 20 – 30 mm (¾ – 1 ¼ in), when they drop to the bottom.
  • The foot fails to develop further, becoming a vestigial organ in the adults.
  • This is a short-lived species, with a life span of only 12 to 26 months.​

Fishing Tips:

Scalloping Tips:

  • Because of their extreme scarcity in our waters, any bay scallops caught should be returned to their environment.
    • With conservation of the bay scallops and the seagrasses in which they live, hopefully their numbers will flourish.
  • A mask and snorkel or a clear plexiglass-bottom bucket can be used to observe scallops in their natural habitat.

Fun Fact:
  • Unlike other species which are bound to some substrate either by burrowing or attachment, adult bay scallops are free-living and extremely motile.
  • They are capable swimmers for short distances, which they accomplish by jetting water through their valves, generally in response to predators.
  • Bay scallops have 18 pairs of blue eyes set in the mantle along the margin of the shell.
  • The eyes can detect shadows and movement, which brings about an escape response.
  • In an attempt to re-establish a population in Chincoteague Bay, MDNR Shellfish Program planted 1.2 million juvenile bay scallops in protective pens and raised them to reproductive age during1997 and 1998.
  • By 2002, live scallops were recorded north of the Ocean City Inlet, possibly for the first time in well over a century.
  • Although low densities suggest that the long-term viability of this scallop population is still in doubt, the extraordinarily rapid range expansion is a major step towards their establishment in Maryland.​

Phylum: Mollusca​


Family: Pectinidae
Order: Ostreoida
Class: Bivalvia

For more information on bay scallops, please contact Mitchell Tarnowski.