- Associated Press - Saturday, April 9, 2016

CHARLESTON, S.C. (AP) - A pregnant turtle clawed her way out of the Ashley River, headed to her nesting site. The cover was gone; the terrain was different. But she climbed on until she was found halfway up the outside staircase of a newly built office off Leeds Avenue.

This is the intrepid diamondback terrapin, the other turtle of the Lowcountry coast, the one whose disappearance might mean the death of the salt marsh.

The state Department of Natural Resources is in the midst of the second round of a multi-year study, capturing terrapins along the lower Ashley River and tagging them to try to get a read on the population and its flux, tracking them by telemetry to see just where they go. It potentially could lead to excluder devices similar to those used on shrimp boats.

Like its far more renowned sea turtle cousins, the salad plate-size terrapin is a species thought to be in long-term decline. The only estuarine turtle in North America, it has a pivotal role in the estuary: it eats marsh periwinkle snails. The snails destroy marsh grass, turning the marsh into mud flats.

That makes the turtle an alpha predator of the marsh, one of those species the ecosystem’s health depends on. The chief reasons for its decline are thought to be development, degraded waters and crab traps.

The DNR study is critically important, said Davidson University biologist Michael Dorcas, who has studied the turtles in the nearby Kiawah River since the 1980s, the longest-running study of diamondback terrapins in the world.

“To know what’s going on with a long-lived species, you have to study them for a long time,” he said.

The onyx-eyed terrapins are gorgeous, spotted and variably colored, with distinct diamond patterns on their shells.

They have been thought to be sedentary. But the female who climbed the office stairs a few years back also has been netted in Charleston Harbor by the James Island Yacht Club some 10 river miles away.

That sort of thing wasn’t known before the DNR study.

The study is a continuation of a 2008-2009 study that established a rough estimate of a few thousand turtles in the lower river. So far, indications are that the population in the river is stable to slightly declining, said Mike Arendt, DNR wildlife biologist.

They have tagged more than 700 turtles so far. The work is cutting-edge enough that U.S. Geological Survey researchers have piggy-backed on it to do wide-range isotope studies on the turtles, trying to gauge if environmental disturbances disrupt the turtles’ diet.

The DNR study “is one of the first few locations to get information,” said survey biologist Matt Denton.

The lower Ashley is considered good habitat for the terrapins. But so few other surveys this concentrated have been done that there’s virtually no point of comparison, particularly with a habitat that’s not so good.

One of the few studies that has been done is Dorcas’ work on the Kiawah, near the embattled Captain Sam’s Spit.

Dorcas has seen a dramatic drop in turtle numbers in the river, from 30 to 40 counts per day in the early years to three or four per day now. He suspects the terrapins there are dying off due to factors such as crab-trap snarls and degradation of the waterway. Meanwhile, he sees evidence that marsh die-off is occurring in spots.

As a control, researchers also surveyed the undeveloped and less crabbed Little Townsend Creek off Botany Island to the south. Its turtle population remains robust.

Kiawah Partners development company plans to build 50 homes in the sand dunes there, with an access road running along a revetment and walled off bank of the river where the turtles nest. Dorcas said he suspects that would be the end of the Kiawah River population.

The same concern for the larger population underlies the DNR study. The marshes are the heart of the estuary, the miles of sweeping grasses vital to its wildlife and water quality, the nursery of countless marine creatures, including shrimp. They are filters that help keep the waters clean.

There are an estimated 400,000 acres now in South Carolina, disappearing acre by acre not only to development but to tidal forces at such a rate that a study in Cape Romain by Baruch Institute Director Jim Morris indicated that as much as half the salt marsh there might be gone in the next 20 or 30 years.

As DNR studies the turtles, Arendt is devising and refining an excluder device for crab traps that ideally would keep turtles out but not keep crabs from coming in.

The device would work with differences in the shape of the creatures and the crab’s tendency to turn sideways to scuttle in the traps while the turtle would try to enter head on. Arendt has made a $50,000 grant proposal to the U.S. Fish and Wildlife Service to pay for testing the device with 300 recreational crabbers.

The device is still in development and factors such as costs and efficiency need to be assessed, and encouraging voluntary use of the devices to test how big a difference it makes might be a next step, said Mel Bell, DNR fisheries director. “We’re not looking at regulations at this point.”


Information from: The Post and Courier, https://www.postandcourier.com

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