There are fresh water turtles (e.g., snapping turtles, red-eared sliders, painted turtles, etc.), there are sea turtles (e.g., leatherback turtles, green turtles, kemp’s ridley turtles, etc.) that live in salt water, and then there are diamondback terrapins (Malaclemys terrapin). Terrapins are the only turtle in North America found brackish coastal tidal marshes, with Cape Cod marking the northernmost extent of their range. Terrapins can tolerate short periods of below freezing temperatures, but not for more than a week or two, which explains why their range has not extended farther north.
The name terrapin actually means “edible turtle”, and speaks to its historic popularity as a culinary delicacy. In the 19th century, the demand for terrapin was so great that the species was nearly hunted to extinction. Although the diamondback terrapin population rebounded after its popularity as food declined, it is once again threatened throughout its range by increased predation and habitat loss. The diamondback terrapin is considered a Threatened species in Massachusetts, and has a similar protected status in many other states as well.
After reading and discussing the book Diamonds in the Marsh: A Natural History of the Diamondback Terrapin by Barbara Brennessel with my natural history bookclub, one of the members described a fairly new monitoring program for terrapin nests being organized by the New England Coastal Wildlife Alliance (NECWA) in Marion and Wareham. I was curious to learn more about the project, as well as find out if any similar work was being done in my own town of Bourne, so I contacted NECWA.
Terrapins lay their eggs in the early summer (generally in June or July in New England). Ideal nesting sites are sandy areas free of vegetation, above the high water line, in close proximity to a salt marsh, which will serve as a refuge for the hatchlings when they emerge in September and October. Aside from observing a female actually dig a nest and lay her eggs, discovering hatched or predated nests in the fall is one of the only ways to locate and count the number of nests in an area. Following my conversation with NECWA’s director, on Sunday I accompanied one of the organization’s volunteers during their regular terrapin nest survey in Marion. We located approximately a dozen recently hatched or predated nests at the site we surveyed; after the hatchlings have emerged from their eggs and exited the nest (or after a predator has excavated the eggs), the nest collapses in on itself, and can be identified by a hole left in the sand. Empty eggs shells are often found in and around the remaining hole.
We also discovered one hatchling in the dune vegetation, and another that had not yet dug its way out of its nest. Interestingly, baby terrapins do not need to eat right away since they are still equipped with a residual yolk sac (see photo below). This yolk sac will continue to provide them nourishment until they are ready to find their own food.