Diamondback Terrapin Still Vulnerable to Human Activities

(Above) Diamondback terrapin: (Malaclemys terrapin)—the most celebrated of American turtles. Once popular as a gourmet-food item, terrapin populations were decimated by collectors in the late 19th and early 20th centuries. New threats to the terrapin's survival include habitat destruction, incidental capture and drowning in crab traps, both commercial and recreational, and death of females on roads when they migrate to nesting sites. "Terrapin" is an Algonquian word that means "turtle." Photograph by Jeff Lovich.

(Below) Some diamondback terrapins have distinctive markings on their heads and carapaces (upper shells). Facial patterns commonly make a terrapin look as if it has a moustache or is wearing lipstick. Photograph by Jeff Lovich. Photograph by Jeff Lovich.
photo of a female diamondback terrapin

The salt marshes and barrier islands of South Carolina appear to be tranquil and idyllic to most people who visit those enchanted shores. Gently waving palmetto trees and stately live oaks grace a landscape punctuated by wind-sculpted maritime forests and seemingly endless expanses of cordgrass and tidal creeks. Here, land and water meet intimately, blurring the distinctions between the two elements in subtle ways that defy the imagination. Beyond this brackish interface are dunes covered in sea oats and sandy beaches, each molded by winds and waves as the land finally gives way to the embrace of the Atlantic Ocean.

This is the home of the diamondback terrapin (Malaclemys terrapin). Terrapins are small turtles, with females rarely exceeding 9 inches in length. Males in the same population are always smaller than adult females. The terrapin is the only species of turtle in the United States that routinely occupies brackish-water habitats, occurring in tidal creeks of estuaries along the Atlantic and Gulf coasts from Cape Cod, MA, to Corpus Christi, TX.

Roger Conant, one of America's most famous herpetologists, called terrapins the "most celebrated of American turtles." His comment was based on the fact that terrapins were heavily exploited as a food source for privileged members of society in the 1800s and early 1900s. With increasing demand for terrapins by epicures, prices soared, and a market was born to supply the big eastern cities of Baltimore, Philadelphia, and New York. Thus, the terrapin became one of the most economically important reptiles in the world.

In recognition of the demand for terrapins, the State of Maryland enacted a law in 1878 providing a closed season and a size limit for the species, but it was almost too late: prices increased with demand, and wild stocks became depleted. In response, the United States Government initiated studies of captive propagation. The terrapin fad finally died out around the time of Prohibition, and populations recovered from the several decades of exploitation. Human activities, however, are once again causing declines in terrapin populations, as shown by various studies, including a long-term population study by myself and others in South Carolina.

Beneath the apparent calm of the terrapin habitat in South Carolina lies a world in tumult. Each day, water levels fluctuate by almost 6 feet as the creeks flush in and out with the inexorable pull of the tide. This fluctuation causes profound changes in the direction and speed of tidal flow, water temperature, and salinity. Punctuating these daily changes are hurricanes that brush or hit Charleston, SC, on average once every 5 1/2 years. Hurricanes commonly generate large storm surges on top of already-impressive tides. According to one source, a hurricane hit Charleston in 1752, causing a storm surge that nearly covered the entire downtown area. When the wind shifted, the water level fell 5 ft in 10 minutes. Given the relatively long lives of terrapins (possibly as much as 40 years), they are likely to live through several hurricanes in South Carolina.

I had the good fortune to study the daily lives and annual cycles of activity of terrapins at Kiawah Island, SC, from 1983 to the present with my colleague Whit Gibbons, a professor of ecology and senior research ecologist at the University of Georgia's Savannah River Ecology Laboratory. What we discovered was amazing. Despite their small size, terrapins are powerful swimmers. Females are capable of making round-trip nesting journeys of more than 5 km from the salt marsh to beach dunes. Yet most terrapins are remarkable homebodies, inhabiting not only the same creek from year to year, but commonly the same small reach of water. Of 442 individuals that were recaptured 1 year or more after their initial capture, only 25 had changed locations from one tidal creek to another. This site fidelity appeared to be unchanged even after such major hurricanes as Hurricane Hugo in 1989, packing 140-mile/hour winds.

On the whole, the ability of terrapins to stay in the same tidal creek despite daily tidal fluctuations and storms is but one reflection of the remarkable resiliency of the salt-marsh ecosystem. Palmettos and cordgrass bend and flex in all but the most severe of hurricanes, and tidal meanders give way to waves and tides in ways that ultimately preserve the characteristics of this dynamic landscape. Severe storms are all part of the cycle of life in the salt-marsh ecosystem, much like fires in forest systems. Only recently have scientists come to appreciate the value of natural disturbances in maintaining the health of ecosystems.

Tim Owens (on left) and Tony Mills of the University of Georgia's Savannah River Ecology Laboratory check nets placed in Terrapin Creek to catch terrapins. The nets commonly caught blue crabs and stingrays, adding to the challenge of working on the project. Photograph by Jeff Lovich.		The Kiawah River provides a corridor for females leaving the marsh to nest on the dunes visible in the background. The dunes are the birthplace of terrapins; just beyond them lies the Atlantic Ocean, birthplace of hurricanes. Photograph by Jeff Lovich.		Jeff Lovich stands near the Kiawah River during high tide, testing the use of radios on terrapins in field pens. The radios presented a real challenge when used in brackish water or saltwater, because the signals will transmit to the receiver only when the antennas are above water. USGS photograph, taken by an Earthwatch volunteer.

Today, the terrapin faces new threats, including death by drowning in blue-crab (Callinectes sapidus) traps, habitat degradation (past and present), and negative interactions associated with human recreational activities. One study suggested that heavy beach use may reduce nesting by terrapins, and noted increased rates of propeller injury on nesting females as boat use increased in the study area. As a result of human impacts, terrapin populations are declining in some areas, with significant local declines documented in Florida and some parts of South Carolina.

The site tenacity of this little turtle makes it especially vulnerable to incidental capture in crab traps set in creeks near public-access points. Limited movement among tidal creeks means that once terrapins are trapped out of one area, a long time will elapse before another population can become established. Without continued protection, the future looks uncertain for the "most celebrated of American turtles."