May/June 2009Disappearing Diamondbacks by Tim Hanson
Once abundant in South Carolina's coastal salt marshes, the diamondback terrapin is in danger of disappearing. Francis Marion University's Peter King is looking for ways to help.
To a casual observer, the nearly imperceptible scratches along Debidue Beach, north of Georgetown, would likely go completely unnoticed. But to biologist Dr. Peter King, the discovery is akin to that of a treasure hunter finding a pirate chest filled with gold doubloons.
The scratches mark the trail of a diamondback terrapin, a diminutive turtle whose numbers have dwindled over the past century until today their status is - depending on individual state designations - either endangered, threatened or unknown. The trail, made by a female terrapin's feet and tail, leads from the water to higher ground where, among the dunes, she has likely dug a hole in the sand to deposit a clutch of oval-shaped eggs before retreating down the beach and into the waters of Winyah Bay's North Inlet.
King, chair of the biology department at Francis Marion University, bends his six-foot frame low to the ground to examine the trail. He snaps some photos with his ever-present digital camera, straightens again to his full height and marches off into the dunes, hoping to find a nest.
"This is very encouraging," says King, whose boundless enthusiasm for his work with terrapins cannot be concealed. "We've seen the trails of three terrapins coming ashore today - and a fourth that may have been frightened by something and turned around part-way up the beach and went back into the water."
King has been studying terrapins at Hobcaw Barony, a sprawling 17,500-acre wildlife refuge and research facility about a mile north of Georgetown, since 2005. His is the first extended terrapin study undertaken at Hobcaw and one of just two current major surveys of the animal in South Carolina. The other study, spearheaded by the Savannah River Ecology Laboratory, began in 1983 at Kiawah Island, south of Charleston.
"I would like this to be an ongoing study that will extend well into the future," says King. "Because there is no development here at Hobcaw, we can record information about the terrapin that would otherwise be very, very difficult to obtain."
Although extended studies of wildlife are rare (a lack of project funding being the usual impediment), King has thus far received ongoing financial and material support. Francis Marion University pays for the lion's share of King's work, and he uses equipment and lab space at the Baruch Marine Field Laboratory at Hobcaw Barony. In 2007, the Belle W. Baruch Foundation, which manages Hobcaw, named King a visiting scholar and awarded him a very welcomed stipend.
There have been several short-term studies related to terrapins conducted during recent years in South Carolina. Graduate students from the College of Charleston have teamed with biologist-advisors from the S.C. Department of Natural Resources' Marine Resources Division on research projects dealing with sonic tracking, hormone signaling, mercury contamination, population estimating and nesting success rates.
The history of the diamondback terrapin resembles that of other animals that have been hunted or trapped nearly to extinction in the United States. When European settlers first arrived in the New World, the terrapin was a common source of food, and accounts of those days indicate the little turtle was abundant all along the East Coast.
In North Carolina, terrapins were so numerous that they became a nuisance to coastal fishermen. In her book Diamonds in the Marsh, author Barbara Brennessel writes that fishermen complained of so many terrapins being inadvertently snagged in their nets that it actually reduced the number of fish they were able to catch. In fact, she writes, so many terrapins became entangled that, because of the collective weight of the turtles, fishermen had difficulty lifting their nets out of the water.
But those days eventually changed as America's upper-crust appetite for turtle soup drove prices of terrapins higher - from a dollar for an entire wagon filled with terrapins to, in some cases, more than a hundred dollars per dozen. This demand, in turn, led to a dramatic increase in the harvesting of diamondbacks.
Today's dwindling terrapin population, which extends along the eastern seaboard from Massachusetts to Texas, is threatened by a variety of factors. In South Carolina, for example, female turtles are often killed while crossing roads in search of dry land to lay their eggs. Offshore, terrapins frequently find their way into crab traps and drown before they are able to get out. In addition, pollution and rapid development of coastal salt marshes contribute to the terrapins' mortality rate.
Studies of the use and efficacy of terrapin excluder devices in blue crab pots have been under way for the past three years by the DNR's Cooperative Research Program, comparing catch rates of commercial crab pots with and without use of the six-inch by two-inch wire or plastic inserts. "Early data suggest that use of the devices reduces or even eliminates bycatch of terrapins, while having little effect on the crab catch," says the program's coordinator, Jason Powers. "Studies from other states have shown that the catch of crabs actually increased in pots using the excluders. Another aspect of our research compares catch rates of different sizes of excluder devices in small creeks where terrapins are known to be present." (Watch for an upcoming article in SCW that tells more about the Cooperative Research Program.)
At Hobcaw Barony, King conducts his research from May through the first part of August, gathering as much field data as possible. Working with a team of Francis Marion University students and enthusiastic volunteers, King gathers terrapins from saltwater marshes around North Inlet.
It is in these marsh areas that the terrapin lives almost exclusively, feeding on tiny periwinkle snails that cling to individual stalks of sea grass. King and his team move into these areas at low tide, using an army-green, fourteen-foot aluminum skiff to carry their equipment.
To catch the terrapins, the team uses a net strung between two poles. With one person wading in brackish water on either side of an estuary - the net (called a seine) spanning the width between them - the pair move forward, driving the terrapins into the net or up onto mud beaches where they are then collected by hand.
"We place the terrapins we catch into a plastic tub and take them back to our boat where each is weighed, sexed, marked and then released," King says. "We probably hold them not longer than thirty or forty minutes."
King uses an ingenious system for marking each terrapin, which makes it possible to identify the individual if it is recaptured a year - or twenty years - later. The system involves cutting a small notch into the edge of the terrapin's shell. The notch corresponds to a number, which is logged along with the weight, size, sex and other information about that particular terrapin.
The number of terrapins captured in a single day varies widely. On some days, King and his assistants will work for hours under the blazing sun, swatting horseflies all day long, and turn up nothing. Other times, their luck turns surprisingly good. On one occasion, for example, King collected thirty-four terrapins in a single day - a researcher's equivalent of hitting the lottery.
In 2008, King and his crew of volunteers captured 147 terrapins - a dramatic increase over the previous couple of years - and he has started to recapture some of the terrapins (thirty-seven so far) that were previously caught, marked and released.
"The battle is not just in the captures," says King. "But it is really the recaptures that provide us with the information."
So far, King's research seems to suggest that individual terrapins live out their lives - if left uninterrupted - in relatively small areas in and around tidal creeks. King calls this phenomenon "high site fidelity."
"We haven't found them moving more than a couple of hundred yards," he says, noting that such information is highly important in the preservation of terrapins when the construction of piers, golf courses or other development is considered. "If you wipe out one nesting area, they may or may not find another one. And that is when the population starts declining."
In the end, King says he would like to see the terrapin receive the same sort of attention from people that is enjoyed by the terrapin's larger, more popular cousin - the sea turtle. Turtle watch patrols organized in various communities along the East Coast act as unofficial protectors of the sea turtle. When turtle nests are found, volunteers in effect stand guard until the young turtles break free of their shells and make their way into the sea.
"The terrapin is an important part of the marine estuary ecosystem," says King. "They deserve the same sort of attention."