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Scallops—General Information

Nineteenth century coal miners took canaries into mines, relying on the birds’ sensitive respiratory systems to warn of low oxygen levels and the presence of dangerous gases long before the air problems could harm humans. Like the miners’ canaries, bay scallops are biomonitors, providing an early warning system for scientists who monitor the quality of Florida’s coastal waters. Scallops are highly sensitive to changes in water quality; therefore, observing their health is a good way to measure the health of an ecosystem. A secretive animal that spends most of its short life hiding in underwater grasses, the bay scallop is a prized dinner entrée for many Floridians and an important part of the marine ecosystem. Historically, the bay scallop was a valuable seafood commodity; however, declining populations in many of Florida’s coastal areas have prompted restrictions, which now allow only recreational harvests.

The bay scallop is a member of the shellfish family known as bivalves, named for its two valves, or shells. Its upper valve is a dark mottled color, occasionally bright yellow or orange, and its lower valve is typically white. Bay scallops may reach a shell height of two inches and live two years; though, in Florida its life span is generally only one year.

The bay scallop feeds continuously by "vacuuming" or filtering small particles of algae and organic matter from the water. It does this by funneling water over open pathways called gills. One of these pathways takes in water and skims off particles, while another expels the filtered water along with digestive wastes.

Scallops open their valves when feeding or breathing and close them when predators approach. The shell can also be slammed shut to avoid silt, which can clog the animal's delicate gills. Many tiny, blue eyes arrayed along the outer rim of the shell detect movement near the animal and serve as a warning system. When threatened, the scallop can swim backwards by clapping its valves and expelling water rapidly.

A bay scallop has the remarkable ability to develop both male and female sexual organs; consequently, the scallop produces both eggs and sperm. Scallops release their sperm and eggs at different times to reduce the chance of inbreeding. The amount of food available and the surrounding water temperature influence development of the reproductive organs. If too little food is present, the scallop will direct all its energy toward survival and will not reproduce.

A change in water temperature can trigger spawning. In Florida, spawning occurs in the fall when the temperature drops. Each scallop is capable of producing millions of eggs at once, but the mortality rate is extremely high. Only one egg out of 12 million may survive to adulthood.

It takes about 36 hours for fertilized eggs to become tiny larvae that float in the water for about 14 days before attaching to the base of seagrass blades. At this time, larvae transform into juvenile scallops, commonly called spat. The spat gradually move up the seagrass blades, out of the reach of bottom-dwelling predators such as crabs. Even then, survival is uncertain. As many as 90 percent of the spat will die within six weeks of latching on to seagrass. Those that do grow large enough to avoid consumption by predators will eventually drop off and fall to the bottom, where they remain the rest of their lives.

One creature, the pea crab, lives in harmony with the bay scallop. This crab finds protection within the scallop's shells. While the pea crab does steal some of the scallop's food, it doesn't take enough to jeopardize the health of its host.

Bay scallops are very sensitive to changes in temperature and salinity. They are also very vulnerable to changes in water quality. Water made cloudy by floating particles and sediments, referred to as turbidity, can clog the scallop's gills. The scallop can close its shell to protect its gills for a short period of time, but it is unable to shut out the dirty water for more than about two hours.

Although bay scallops were once plentiful throughout Florida's west coast, they have virtually disappeared in some areas. An extensive scallop fishery existed in Tampa Bay as recently as the 1960s, but scallops are rarely found there now. Charlotte Harbor also supported a commercial fishery some 30 years ago. Scientists believe poor water quality is responsible for these declines. Currently, the most extensive bay scallop populations are located north and west of the Suwannee River, particularly near the fishing hamlet of Steinhatchee and in St. Joseph Bay.

Harvest of bay scallops for commercial sale is illegal in Florida. Recreational harvest for personal consumption is allowed only north of the Suwannee River and only between July 1 and September 10 of each year. Each person is allowed two gallons of whole scallops, or the equivalent of one pint of shucked meat, per day. The limit for each boat is 10 gallons of whole scallops or one-half gallon of meat per day, but the individual limit applies when fewer than five people occupy the boat. A saltwater fishing license is required if using a mask and snorkel or if fishing from a boat. Scallop harvesting is very popular in the Steinhatchee vicinity, St. Joseph Bay, and areas around St. Marks and St. Andrews Bay.