The story of Bermuda’s diamondback terrapin population is one of survival against the odds. Today they exist exclusively within the confines of the Mid Ocean Club golf course, spending most of their time in four brackish ponds close to the fifth and eleventh holes. They face a range of threats to their fragile existence from the decline of the mangroves where they can feed and hide from predators, attacks on their young by the yellow-crowned night heron, and pollution in the ponds.
Dr Mark Outerbridge, a wildlife ecologist who has worked for the Department of Conservation Services for the past ten years, has been involved in multipronged efforts to give the shy and enigmatic creatures a helping hand in their quest for survival. His early contributions were in the form of research. A 2008 paper he coauthored left little room for doubt that Bermuda’s diamondback terrapin population is native, not introduced. The evidence was partly palaeontologic—a terrapin fossil found in a Hamilton Parish cave by conservationist David Wingate that radiometric analysis suggested was more than 400 years old.
Genetics were also key, as the Bermuda population’s close genetic resemblance to diamondbacks found in the Carolinas supported the theory that the terrapins originally came to the island naturally in the Gulf Stream. The species is found in coastal regions from Texas up to Massachusetts and genetic differences exist between the populations at different latitudes. “The paper was able to put bookends on the antiquity of the terrapins here,” Dr Outerbridge said. “The ancient bones indicated that they have been here at least 500 years, but probably not more than 3,000 years because that would predate the age of the mangrove swamps that they would have needed to survive.” The conclusion of the paper explained the significance of its findings for the terrapins: “The native status for Bermudian terrapins resolves its uncertain conservation status and should afford it full legislative protection and appropriate conservation measures.”
Standing high above Mangrove Lake, better known to golfers as the water hazard at the fifth hole, Dr Outerbridge speculated on how the first terrapins to arrive established themselves. “There’s an eighteenth-century hand-drawn map that shows this pond as an actual bay connecting to south shore, and where Pink Beach is there was a neck of sand,” Dr Outerbridge said. “That may be where they came ashore and where they nested.”
The arrival of South Shore Road in the nineteenth century would have created challenges for the terrapins to get from the ponds to the beach. But the development of the golf course in the 1930s came to their rescue, with the installation of sand traps—ideal nesting locations. “I think the terrapins transitioned from living a natural lifestyle in a natural environment to an artificial one in an artificial environment,” Dr Outerbridge said. “Since the 1930s, they’ve been basically a captive population on the golf course. But the course is fulfilling their habitat needs—places to nest, mangroves where the young can grow up and feed. And the water hazards are where the adults spend their lives.”
Had the golf course never been built, what would have happened to the terrapins, after the road cut off access to the beach? “My feeling is they probably would have just fizzled out, because while adults survive in the ponds and they would have tried nesting in muddy spots, the population would have collapsed eventually,” he said.
After his 2008 paper established the diamondback terrapin as a new native species, Dr Outerbridge proposed that a student carry out a PhD study of the terrapins—but there were no takers, so in 2010, he took it on himself. Spending four years researching the population, he estimated there were between 100 and 150 terrapins. “That then led to a management plan and to today’s conservation efforts,” he said.
Dr Outerbridge was aware that in the US, diamondbacks face numerous threats. Racoons sniff out nests and eat the eggs; birds, rats and other mammals prey on youngsters emerging after hatching, while adults fall foul of crocodiles in the water, or cars while crossing roads to reach nesting grounds. The Bermudian terrapins face different, but equally serious threats. The major issue is vehicle-related contaminants, such as heavy metals from disc brakes and hydrocarbons in exhaust emissions, which wash off the roads and find their way into the ponds. “The chemicals are mostly locked in the sediment,” Dr Outerbridge said. “We know that the snails eating that sediment have high levels of contaminants and those snails are the terrapins’ primary food source.”
Without diamondbacks sufficient to conduct mortality tests, Dr Outerbridge used red-eared sliders—invasive terrapins imported as pets and released into the wild by their owners—as a substitute. He found that deformities of the liver and the reproductive system were common. In a reproductive study, he found that of the eggs being laid by diamondbacks, 70 percent were not hatching and that the eggs frequently contained high levels of contaminants.
Potential solutions to the pollution issue are focused on two aspects: reducing the inflow of toxins and cleaning up the ponds. Creating “a series of bio sponges between the road and the ponds” is one approach: Soakaways, for example, that allow for sediment to get trapped in rocks containing bacteria capable of breaking down many contaminants, or strategically placed mini-wetlands planted with flora that excel in ‘sucking up’ contaminants.” Cleaning the ponds is also possible. “The sediment now is a hot mess,” Dr Outerbridge said. “But you can literally seal it using diatomaceous earth and press the reset button—but you wouldn’t do that unless you were also reducing the input of contaminants.”
Dr Outerbridge also teamed up with others, including Dr Jamie Bacon, education officer and research associate at the Bermuda Zoological Society, to conduct an aeration trial, injecting bubbles into part of a pond to encourage aerobic bacteria. This resulted in a significant decline in hydrocarbon pollutants that these microbes break down. Stripping out invasive flora encroaching at the edge of Trott’s Pond and planting more mangroves would also boost the terrapins’ survival hopes. All the solutions would require significant investments and the cooperation of the Mid Ocean Club, but Dr Outerbridge is quick to point out that other species, and the environment as a whole, would benefit too.
Staff at the club have learned to coexist happily with the reptilian life members in their midst. Dr Outerbridge has previously given talks to staff and some club members, educating them on the history, habits and needs of the terrapins. He has seen that some golfers love to see the creatures around—others are totally focussed on their game. “I’ve seen a guy try to get the ball out of a sand trap and not even notice that there’s a terrapin nesting just a few feet away!”
While Dr Outerbridge believes the club takes pride in its role in helping a unique and vulnerable population to survive, the conservationist and golfing viewpoints do not always align. He urged the greenkeeper, for example, to let the grass grow into the water around the edges of the ponds to create places where young terrapins could hide from predators. However, “They let it grow for a couple of years and then got complaints that the water hazards were looking ugly, so they cut the grass. This is a privately owned property, and the conservation world is not always going to get its way—I understand that and I appreciate that they allow me to do my conservation work here.”
But Dr Outerbridge remains passionate in advocating on behalf of a species that settled Bermuda before humans and now needs a helping hand from us to survive.