Diamondback Terrapins

The diamondback terrapin, Malaclemys terrapin, is an icon of the Chesapeake Bay region, serving as the official state reptile of Maryland and the mascot of the University of Maryland at College Park. Found along shorelines from Cape Cod to Texas, it is the only North American turtle that lives exclusively in the brackish waters of estuaries, bays, and salt marshes. The carapace of each animal has markings as unique as a zebra’s stripes or a human’s fingerprints and the pattern on its shell gives the diamondback its name.

The subspecies found in Chesapeake Bay, the Northern diamondback terrapin, grows larger than any other diamondback. Males can reach six inches, while the generally larger females may grow up to nine inches. Terrapins primarily eat mollusks such as snails, clams, and mussels, their strong, sharp beaks allowing them to break their prey’s hard shell.

Though terrapins can live longer than forty years, less than twenty percent of eggs laid actually survive the first year. Predators such as foxes, raccoons, and skunks prey on eggs and juveniles.

As diamondbacks mature, threats largely shift from natural predators to human-induced challenges. For years there was only a small fishery for terrapins in the Chesapeake, but by 2006 harvests had grown considerably in response to demand from foreign markets. The increased catch spawned a heated controversy over the taking of these charismatic turtles and in 2007 commercial terrapin harvest in Maryland was banned. (See “Terrapins as Food.”)

But even without a commercial harvest, threats to terrapin survival persist. Many adult diamondbacks are killed by cars while crossing roads, by boat strikes, and when accidentally caught in crab or eel pots. Habitat loss also threatens terrapins, as coastal development alters important nesting areas.

Terrapins as Food

The word “terrapin” is traced to an Algonquin Indian term for an edible turtle that lives in brackish water. Early Chesapeake colonists prepared terrapin, just as the Native Americans did, by roasting them whole over live coals. By the late 19th century terrapin had evolved into a delicacy enjoyed by the wealthy. Terrapin soup made with sherry and cream was so popular that the turtles were hunted relentlessly and, by some accounts, barely escaped extinction. In 1891, watermen pulled more than 89,000 pounds of terrapin from the waters of the Chesapeake Bay.

The early 20th century granted the species a reprieve as national events squelched the intense demand for terrapin. Prohibition outlawed alcohol, which was used to make terrapin soup, and the Great Depression forced tastes to shift away from expensive gourmet delicacies.

A widespread appetite for terrapin never returned in the United States, resulting in decades of only small terrapin harvests. But by the late 1990s, this trend changed. Depleted turtle populations in Asia left Asian seafood markets looking elsewhere to satisfy their consumers’ demand for turtle — a popular and culturally significant Asian dish. With terrapin harvest banned throughout much of the U.S. east coast — but not in Maryland — Chesapeake watermen had captured a new market. Harvests increased from just under 400 pounds in 2002 to over 14,500 pounds in 2004. Demand continued, and the Maryland Department of Natural Resources reported the wholesale price of terrapin for food markets doubled in 2006.

Many scientists and conservationists argued that the declining diamondback terrapin population could not rebound given such levels of exploitation. The curator at the National Aquarium in Baltimore even noted that terrapins might be on a “slow spiral to extinction.” After harvest rules adopted in 2006 resulted in unintended consequences, including a twenty-fold increase in the number of turtles trapped, some conservationists and others called for a complete moratorium on commercial harvest. In March 2007 Maryland’s state legislature overwhelmingly voted in favor of a ban, mandating the moratorium go into effect the following summer.

Maryland Sea Grant Research

Bycatch, the catch of non-targeted marine life in fishing gear, plagues many of the world’s fisheries. Lines set for tuna can accidentally catch sea birds, trawl nets fishing for pollock can bring up salmon — and pots set for crabs or eels can trap diamondback terrapins. Maryland Sea Grant has funded research by terrapin scientist Willem Roosenburg to discover ways to reduce the accidental drowning of terrapins in pots. Roosenburg has worked to determine the overlap between critical terrapin habitat and commercial crab and eel pot fisheries. He has also developed a Bycatch Reduction Device (BRD) for eel pots, which makes it more difficult for terrapins to enter the pots. His research shows that eel pots with BRDs are effective at minimizing terrapin bycatch without compromising the pots’ ability to capture eels. Although BRDs are not yet required in eel pots, Roosenburg feels they are an avenue worth pursuing in the prevention of terrapin bycatch.

Useful Links

University of Delaware
Diamondback Terrapin

Bay Journal
Terrapin Harvest Ban