Published on November 8, 2021

Diamondback Terrapin Survey Results

Diamondback Terrapins (Malaclemys terrapin) are brackish water turtles with a home range from Texas to Massachusetts. Here in The Bay State, they are listed as threatened, meaning they are likely to become endangered in the foreseeable future. While some of their largest populations in Massachusetts are on Cape Cod, the South Coast also plays host to significant numbers of individuals across the estuaries of Buzzards Bay.

Diamondback Terrapin hatchling in hand

On the South Coast

While terrapin sightings have been sporadically reported over the years at Mass Audubon’s Allens Pond and Great Neck wildlife sanctuaries (Westport and Wareham, respectively), official records were never kept.

To better understand how this species is using our sanctuaries, we conducted a pilot study during June and July of the 2021 nesting season. To ensure the accuracy of the collected data, we provided both in-person and online trainings for those who volunteered to help. Our study employed two different survey methods—activity and head count.

Activity Surveys

To minimize human disturbance, volunteers were trained to remain very quiet and observe the turtles through binoculars to facilitate keeping a safe distance from them. Volunteers looked for and recorded the presence of actual turtles as well as any signs of their land activity, including:

  • Tracks: marks in the sand indicating turtle movement
  • False nests: places where a turtle started to dig a nest but then stopped due to disturbance or site unsuitability
  • Predated nests: former nest sites surrounded by shards from eggs that were dug up and eaten by a predator such as a raccoon, fox, or coyote

Head Count Surveys

Also referred to as “rapid visual assessment,” head count surveys utilize a method developed by a group of researchers including former Mass Audubon biologist Patricia Levasseur. For this method, volunteers stand at a predetermined location to look for turtle heads protruding above the water’s surface. They are trained to visually scan the surface of the water in a 100-meter semicircle to count the heads, moving in only one direction to ensure that individuals are not accidentally recounted.

Diamondback Terrapin in marsh grass

What We Learned

Allens Pond Wildlife Sanctuary:
Westport, MA

We saw terrapins both in the water and on land, and recorded four predated nests. These findings are hopeful, as they confirm we have nesting activity here. Going forward, we would like to expand the rapid visual assessment surveys to get a better overview of turtle activity at the site, and look into securing permits to implement protective measures on the nests to prevent predation.

Great Neck Wildlife Sanctuary:
Wareham, MA

We’ve been working hard to restore this site’s marsh edge habitat with the specific goal of providing a nesting area for turtles. We removed an asphalt court and replanted the area using the Mass Wildlife Natural Heritage and Endangered Species (NHESP) guidelines for creating turtle nesting habitat. Next we are removing the invasive plants growing between the court's former footprint and the marsh.  

This work is part of a Southeast New England Program (SNEP) Watershed Grant, funded by the U.S. Environmental Protection Agency (EPA) through a collaboration with Restore America’s Estuaries (RAE). Learn more about the work Mass Audubon is doing under this grant.

In our 2021 survey of Great Neck, terrapins were seen only in the water, not on land. This is the first official documentation of terrapins in the marsh at this sanctuary, and we are encouraged to see that they are already using this site for important activities such as mating and foraging.

Future Plans

We will use the information gathered in this pilot study to plan for continued monitoring in the summer of 2022 and beyond. If you’re interested in helping out, please complete our volunteer interest form and select “Turtle monitoring” as an answer to question 12.   

We look forward to collecting additional data in the coming years, and using that information to help inform future land management decisions.