Diamondback Terrapins Making R.I. Comeback

By TODD McLEISH/ecoRI News contributor

Diamondback terrapins are the only turtle in the Ocean State adapted for life in salt marshes, coves and other quiet brackish waters. (Rhode Island Natural History Survey)

Diamondback terrapins are the only turtle in the Ocean State adapted for life in salt marshes, coves and other quiet brackish waters. (Rhode Island Natural History Survey)

One of Rhode Island’s rarest turtle, the diamondback terrapin, has been discovered in new locations in recent years, and those monitoring the animals say the species is holding its own in the state and may even be increasing in number.

The only turtle in the state adapted for life in salt marshes, coves and other quiet brackish waters, diamondback terrapins have been closely watched for at least 27 years at their major stronghold in Barrington’s Hundred Acre Cove. That’s how long Charlotte Sornborger has been monitoring their nesting success there.

Every year in late May and June, she and a team of volunteers watch as the female terrapins emerge from the water to lay their eggs in farm fields and other sites with sandy soils adjacent to the cove. She estimates that about 550 terrapins breed in the area.

“The population seems to be sustaining itself,” she said. “They could be growing, too, though maybe we’re just getting better at counting them.”

It takes about 65 to 70 days for terrapin eggs to hatch, with the last ones this year emerging from their nests on Labor Day weekend.

Coyotes, skunks and raccoons used to scavenge the eggs in many of the nests, destroying between 200 and 300 nests annually. But that was before Sornborger began protecting the nests with wire mesh “excluders,” which prohibit mammalian scavengers from digging down to reach the eggs 6 inches below the surface.

Sornborger said “a decent population” of diamondback terrapins is also found in the mouth of the nearby Palmer River, but she has been unable to learn exactly where they nest, so no one knows how many are there.

Small numbers of terrapins have recently been discovered in the vicinity of Smith’s Cove, Jacob’s Point and Colt State Park, all in the Bristol and Warren area.

“We don’t know where they nest at any of those locations either,” she said. “It’s possible the Hundred Acre Cove population is on the move, so they may have come from there.”

But, Sornborger said, the terrapins may have always been at those locations and no one has ever noticed them before.

That’s likely the case in Westerly, too, where a few terrapins have been found at Napatree Point in recent years.

“We found a dead terrapin at the end of June, but nothing since,” said Janice Sassi, director of the Watch Hill Conservancy. “There were indications the past two years that they are nesting.”

A determined effort by the Rhode Island Natural History Survey in 2013 also found about 15 terrapins in some of the coastal salt ponds in South County.

The biggest surprise, however, was the recent discovery of a significant population of diamondback terrapins nesting at a private beach at Rocky Hill School, at the mouth of the Hunt River in Warwick.

Laura Meyerson, associate professor of natural resources science at the University of Rhode Island, was shown a video of a terrapin hatchling on the beach two years ago and learned that a teacher at the school has known about the population for several years.

“We think they’ve been there for a while,” she said. “It’s a quiet, protected beach on the Rocky Hill property, so there aren’t a lot of people there to notice them or disturb them.”

Meyerson received a grant from the National Science Foundation to monitor the Rocky Hill terrapins with Rochelle Devault, a science teacher at the school. Along with students from URI and Rocky Hill, they were pleased to observe 87 nests this summer, but unfortunately all but three were eaten by foxes, raccoons, skunks and domestic dogs.

“It’s not a good situation,” Meyerson said. “We didn’t observe any hatchlings at all, though the terrapins hide their nests well — they’re masters of camouflage — so it’s possible we missed some.”

Devault said there may be many more terrapins than the 87 they observed.

“Our population is extremely shy,” she said. “The number of live terrapins I’ve seen in the water is pretty high, but the number that come on land to nest is far reduced from those I see in the water. They look up at me and turn around and head back in the water.”

As a result, the terrapin monitors at Rocky Hill now hide behind nearby vegetation as they keep track of the nesting turtles.

Meyerson and Devault plan to explore other marshes near Rocky Hill next year to look for additional terrapin nesting locations. They also will install signage to direct dog walkers away from the nesting area. They hope to learn from Sornborger how to better use excluders to protect the nests.

“We definitely have to figure out how to do a better job at limiting predation,” Meyerson said. “We really want to build some momentum at the school to protect the terrapins.”

Rhode Island resident and author Todd McLeish runs a wildlife blog.