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Diamondbacks in the Marsh

By Tom Richardson

It wasn’t until 2005 that I had even heard of diamondback terrapins, the only estuarine turtle in North America, even though I had spent a good deal of time in their habitat. It turns out that these secretive reptiles had been living right under my nose the entire time!

A female diamondback lays its eggs in a sandy nest in Wareham, MA.

Diamondback terrapins range from Cape Cod in the north to Florida in the south and west to Texas, often living in small, localized populations. Now a threatened species in New England, they were once abundant throughout coastal America. But the tide turned against the turtles in the 1800s, when terrapins were considered haute cuisine and nearly hunted to extinction, until saved by the Great Depression.

Newly hatched diamondback terrapins at the Mass Audubon Wellfleet Bay Wildlife Sanctuary on Cape Cod.

Today, the greatest threats to diamondbacks are the destruction of their nesting habitat and predation of their eggs by raccoons, foxes, coyotes, opossums, skunks, and dogs. In some areas, it’s estimated that 95 out of 100 turtle nests are predated by animals. That’s why conservation organizations such as MassAudubon try to locate the turtle nests and relocate them to safe areas protected by wire cages. After roughly 55 days, the protected nests are monitored for hatchlings, which are released into the wild.

Female diamondbacks, which grow to a maximum length of about nine inches, nest twice a year in the Northeast. The first nesting phase occurs from early to mid-June; the second from late June through mid-July. Nests are dug during the day, often around high tide, to limit exposure to predators.

Like many turtles, diamondbacks nest in the same areas where they were hatched. When the female locates a suitable site—usually an area of sandy soil well above the high tide line—she scoops out a small hole about the size of a light bulb, into which she deposits 12 to 13 pink, leathery eggs. She then covers the nest, smoothing the surface to blend in with the surrounding soil. Once the disturbed soil dries, it’s nearly impossible to identify the nest.

The baby terrapins emerge from the nest between mid-August and mid-October and head for the coastal forest, where they spend the next two to three years foraging on insects, worms, and other invertebrates, as well as vegetation.

Once the turtles reach a size of five or six inches, they have almost no natural predators. However, since they often forage on dead fish and other animals (even whales and dolphins that wash into the marsh), they are occasionally caught in baited crab and conch traps placed near shore. Some turtles are also killed by powerboats and personal watercraft operating in shallow water. During nesting season, many female turtles are killed by vehicles while moving between their nest and the marsh.

Adult diamondbacks spend nearly all of their time in the water, and can stay submerged for very long periods. When the water temperature drops below 55 degrees or so, they bury in the muddy bottom and enter a hibernation-like state known as brumation, during which they absorb oxygen through their skin.

Diamondbacks are remarkably resistant to disease, too, and once they make it past the vulnerable juvenile stage they can live for a very long time—perhaps 70 or 80 years.

The best way to spot the secretive terrapins in the wild is by looking for their tiny, black heads poking above the surface. In some areas, the turtles can be quite numerous, and you may spot over a dozen by patiently scanning the water. If you kayak in shallow marsh creeks, you may spy them swimming under the surface. And during nesting season, if you are lucky, you may come across a female terrapin depositing her eggs in a sandy area between the forest and the marsh.

As mentioned, habitat loss poses a major threat to diamondbacks. The destruction or draining of marshlands for development can wipe out an entire population of turtles. Also, the construction of breakwalls and coastal roads can prevent the turtles from reaching their nesting sites.

Interested in learning more about diamondback terrapins? Check out the New England Coastal Wildlife Alliance.



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