Diamondbacks of New England
June 15, 2020
In the fall of 1998, Sue Wieber Nourse was lecturing in her marine science lab at Tabor Academy in Marion, Massachusetts, when a small, olive turtle scrambled across the threshold of the open door and into the room. Unsure of what species it was, she checked it against her reference sources and identified it as a juvenile diamondback terrapin, the only estuarine turtle in North America. What made the discovery especially intriguing was that diamondback terrapins were thought to be extinct in the Marion area, where shoreline development has eliminated much of their habitat.
It wasn’t until a few years later that Wieber Nourse attended a talk given by turtle researcher Don Lewis. When she told Lewis of her discovery, he immediately volunteered to scout the Marion waterfront for likely diamondback habitat. By the time their investigations were over, Wieber Nourse and Lewis had found several spots where the turtles might still be able to live, breed and nest. And two years later they were married, brought together by a most unlikely matchmaker.
Lewis and Nourse, who have since moved south, met a lot of people through turtles, including this writer, who read about the Marion discovery in a local newspaper. While that alone was enough to pique my interest, the same article also mentioned that nesting diamondbacks had been found in a small cove just steps from my house.
Terrapins among us? This was news indeed!
Hunting for Terrapins
I got in touch with Don, who invited me to join him and Sue, along with their son Jared and several interns from Wheaton College, on a diamondback census in Cape Cod’s Wellfleet Harbor. Wellfleet, more specifically the expansive network of tidal flats, creeks and marshes surrounding Lieutenant Island, is home to the northernmost population of diamondbacks in the world. With hundreds of adult turtles inhabiting this one small area, it’s a robust population, largely because the land around Lieutenant Island remains relatively undeveloped. The area features acres of channel-etched salt marsh bordered by pristine tidal flats and sandy uplands—ideal terrapin habitat.
Diamondback terrapins range from Cape Cod in the north to Florida in the south and west to Texas, often living in small, localized populations. Once abundant throughout coastal America (George Washington’s ragged army apparently caught a good deal of terrapins during the infamous Valley Forge winter by “poling” for them as the turtles lay dormant in the Delaware River mud), diamondbacks were nearly hunted into extinction for haute cuisine dishes in East Coast cities until saved by the Great Depression.
In Massachusetts, diamondbacks are listed as “threatened,” with turtles in more developed areas under greater pressure. “In the southeastern part of the state, where human development has been more intense and of longer duration than, say, the northern end of Cape Cod, we have altered the coastal ecosystem in ways that have severely impacted terrapin habitat,” says Lewis. “Within the Massachusetts South Coast region [Cape Cod to Rhode Island], I would assess their situation as critically pressured and on the verge of extinction in some of the more developed estuary systems, such as Sippican Harbor and the Mattapoisett River. They may already have been completely extirpated from New Bedford Harbor and the Acushnet estuary. Then again, we thought they were gone from the Taunton River system, yet we found a few—a small residual population—in Assonet Bay in Freetown a couple of years ago.”
When I joined Don, Sue, and their team on their census expedition in June, we found several nests and lots of adult turtles. Lewis often relocated the eggs to a safer location and surrounded the site with a wire-mesh basket to keep out predators. “We estimate that 95 out of 100 turtle nests are depredated by animals, mainly foxes, skunks, raccoons and opossums,” he told me.
Where They Nest
According to Lewis, 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. Nesting usually occurs during the day, with the females timing their efforts around the high tide, to limit their exposure to predators.
Like many turtles, diamondbacks nest in the same areas where they were hatched. They like to nest next to the marsh, in loose, sandy soil. When the female locates a suitable site, she scoops out a small hole about the size and shape of an inverted lightbulb, into which she deposits 12 to 13 pinkish, leathery eggs, each the size of a large olive. She then covers the nest, smoothing the surface to blend in with the surrounding soil. “Once the sun dries the sand, you’d never know there was a nest there,” says Lewis. “A terrapin nest is very hard to spot. It fact, it took us almost 20 years to learn what to look for.”
The turtles hatch between late August and mid-October. They leave the nest in daylight, crawling one at a time through a hole about the size of a quarter. “It’s like the scene in ‘The Great Escape’, when the prisoners are darting out of the tunnel one at a time,” says Lewis. “The hole is just big enough for them to squiggle through. After they’re all out, the nest cavity collapses and looks like the surrounding sand. That’s why empty nests are hardly ever found.”
Even with the help of humans to protect the hatchlings and get them to the water, it’s estimated that only one in 250 turtles reaches adulthood, which takes eight or nine years. “Just about everything eats them,” Lewis says, rattling off a list of predators that includes herons, gulls, blackbirds, bluefish and striped bass. “I imagine they must be something like potato chips—salty and crunchy.”
The good news is that once the turtles reach “hockey puck” size, they have almost no natural predators, largely due to their hard shells and ability to blend in with their marshy surroundings. Only humans pose a lethal threat to adult diamondbacks, by inadvertently drowning them in underwater traps or running them over when they come ashore to nest.
Fortunately, diamondbacks spend nearly their entire lives in the water, and can stay submerged for up to 20 minutes. 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. On the other hand, a slow growth rate, low recruitment and longevity make diamondback populations susceptible to crashes.
“You may see a lot of adult turtles around for many years, but no young turtles entering the population,” Lewis explains. “It’s the same situation that occurs with many turtles, including the [protected] Eastern box turtle. If there is no recruitment, the population in that area will disappear once the adults die off.”
However, the biggest threat to diamondbacks isn’t predators, but the destruction and alteration of their habitat. They need pristine marshes and open access to nesting sites. Seawalls, paved roads and steep drainage ditches pose major threats to the adult turtles’ ability to reach the nesting areas. When their offspring hatch, these same barriers prevent them from reaching the safety of the water.
To Catch a Diamondback
On the day of the turtle census in Wellfleet, I watched as Lewis and his volunteers went about catching turtles. They did so with long-handled crab nets and buckets. The hunt took place at low tide, when the marsh creeks were dry, forcing the turtles to concentrate in the shallow water covering the flats and sandbars.
The best way to spot terrapins is by looking for their tiny black heads poking above the surface. It’s not easy, especially in choppy water. With a turtle in his sights, the hunter must move quickly, because the terrapin will immediately dive for the bottom once it senses danger.
Once a turtle was captured, it was weighed, measured, photographed, and marked with identifying notches on the edge of their carapace before being released. Recapture rates of marked turtles signal the relative health of a population. High and increasing recapture rates indicate few recruits and a population on the decline; low and decreasing recapture rates reveal a vibrant and growing population.
To determine a turtle’s age, researchers count the growth rings on the scutes—the series of plates that form the carapace. The rings are similar to those in a tree trunk cross-section, with each ring representing a year in the turtle’s life. The researchers also draw blood, which is used to analyze their genetic structure.
Lewis explained that terrapins from different geographic areas, and even those within the same region, exhibit unique behaviors and are “programmed” to nest in the specific area where they were born—key reasons why transplanting them to increase a depleted population is seldom effective. “However, we can boost a local population simply by getting people to report sightings, so that we can find and protect the nests in those areas,” Lewis points out. He adds that, like in Marion, diamondbacks are turning up in places where they were thought to have been wiped out years ago.
Scouting for Diamondbacks: What to Look For
Diamondback terrapins are incredibly secretive and hard to find, especially since they spend most of their lives underwater and are well camouflaged. However, if you know where and what to look for, you might be able to find some right under your nose.
Here are some clues:
- Prime habitat includes large tracts of undeveloped saltwater marsh bordered by sandy uplands. There should be a lack of seawalls, ditches and paved roads.
- From late May through mid-July (nesting season), look for turtle tracks and nest sites in sandy areas above the high-tide mark.
- Look for holes and egg shards from depredated nest sites.
- Look for a small discolored or damp patch of sand surrounded by dry sand, which may indicate a freshly dug nest.
- From May through September, look for small, black turtle heads poking above the surface in one to three feet of water over shallow mud or sand flats.
- Look for turtles swimming through marsh-lined creeks or hugging the grassy banks.
- In early fall, look for shallow depressions and egg shards left by emerging diamondbacks.