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Living Sanibel: Calico scallops common find on Sanibel beaches

By Staff | Jun 24, 2015

Bay Scallop PHOTO PROVIDED

One of the most commonly found shells on the beaches of Sanibel and Captiva, the calico scallop is also one of the most beautiful. It washes ashore in a vast array of colors and is fairly resistant to damage in the rough-and-tumble world of the surf zone. The calico scallop is widely used in shell art and for decorative purposes. It has the classic shell shape made popular by the Shell Oil Company, and it is the centerpiece of one of the world’s most famous paintings, “The Birth of Venus” by Botticelli.

Although calico scallop shells are easy to find and identify on the beach, it presents a much more difficult challenge to find one alive. Because it is free swimming, it occasionally washes up alive on the beaches after a major storm. Under normal circumstances the best place to find a live calico scallop is in a tide pool, sitting on the bottom in ankle- to waist-deep water.

The calico is widespread and is not as commercially harvested as the bay scallop. It ranges from Delaware to Brazil. Like all scallops, the calico is a filter feeder, taking in vast amounts of seawater and removing microscopic particles of algae, diatoms, and other phytoplankton. It is eaten by rays, nurse sharks, and a number of other fish.

Atlantic Bay Scallop

A combination of over-harvesting and habitat loss has placed this once-common species in serious decline. In the early 1950s, up to 120,000 pounds of bay scallops were taken out of Pine Island Sound annually. Today it is difficult to find even a small bucketful during the summer scallop season. This same situation exists in Sarasota and Tampa; the only remaining viable populations are found north of the Crystal River and in St. Joseph Bay in the Florida Panhandle.

Most of the bay scallops purchased at the local fish market are commercially grown, while the wild populations throughout the U.S. have been steadily declining over the past 60 years. Efforts to reseed various populations have thus far been disappointing, though various organizations, including the Marine Lab at SCCF, remain committed to bringing this once-plentiful species back into our estuaries.

One of the only mobile bivalves, the bay scallop is capable of free-swimming behavior. It does so by rapidly opening and closing its shell, jetting out the water, and propelling itself through the sea grasses with surprising speed. This swimming ability helps it to escape predators such as stingrays and cow-nosed rays. The bay scallop also has dozens of tiny blue eyes that run along the entire outer edge of the shell when opened. These eyes cannot see objects per se, but help the shellfish detect and flee potential predators.

Look for Atlantic bay scallops in the back bays, especially in the sea grass beds. The best method of finding a wild scallop is by snorkeling, though you might be able to spot one from a kayak, or canoe, if the water is clear.

The scallop is taken by wading birds, otters, and any number of sharks and rays, but its biggest threat comes from changes in its environment brought about by human activities. The building of the Sanibel Causeway in the early 1960s was reputed to change the salinity of San Carlos Bay, thereby destroying vast scallop beds in the tidal flats between Sanibel and Punta Rassa.

This is an excerpt from Living Sanibel – A Nature Guide to Sanibel & Captiva Islands by Charles Sobczak. The book is available at all the Island bookstores, Baileys, Jerry’s and your favorite online sites.