Northern Diamondback Terrapin Spotting Porgram

(Malaclemys terrapin)

Northern Jersey Shore Terrapin Spotting Program

In 2020, Save Coastal Wildlife will began a study on diamondback terrapins Malaclemys terrapin in the wetlands and bayside beaches of the Northern Jersey Shore, primarily along Raritan Bay, Sandy Hook Bay, Navesink & Shrewsbury Rivers, and along the Shark River. Information will be given to NJ Fish and Wildlife to better map the population of Diamondback terrapins in New Jersey, which is currently listed as a “species of special concern,” due to the loss of breeding habitat and decreasing population numbers.

Members of Save Coastal Wildlife will walk wetland areas and beaches in search of female terrapins coming up onto bayside beaches to nest. The diamondback terrapin is the only brackish-water turtle in New Jersey.

Become part of our Terrapin Spotting Project by getting involved. Save Coastal Wildlife is looking for dedicated people who will help to spot diamondback terrapin nesting sites in Monmouth County, NJ from April to October. An ongoing identification program is crucial to the continued protection of this species in our region. No experience is required (we will train) – you only need enthusiasm! Our terrapin work depends almost entirely on volunteers.

If you see a diamondback terrapin on a beach or in a wetland, please report your sightings below.

Needed Information:

  • Date and Time

  • General location

  • Latitude and Longitude (decimal degrees preferred)

  • Take photos

  • What was spotted? Nest or Terrapin?

  • If nest, intact or disturbed?

  • If Terrapin, how many observed? Alive or dead? In water or on land?


What is a Diamondback Terrapin?

They are not sea turtles and they do not live in freshwater! Northern Diamondback terrapins are the only brackish water (where salt water from the ocean mixes with fresh water) turtles in the United States.  These unique turtles prefer to live in salt marshes, tidal rivers and bays and can be used as an indicator species of the health of an estuary.  

Females only come ashore to nest and lay eggs. Males remain in the water. Although the terrapins are usually found in brackish water, they occasionally travel out into the nearby ocean to forage for food. Diamondback terrapins, however, cannot tolerate full-strength salty water for long periods of time or they will dehydrate and die.

Description: Diamondback terrapins have a gray, light brown, or black top shell (carapace) that is broad and patterned with concentric rings or ridges. The carapace is also wedge-shaped, and when viewed from above, the widest part is in the rear. The under shell (plastron) can range from yellowish to greenish gray, with or without bold, dark markings. The large feet are webbed, and the head and limbs may be spotted.

Male terrapins are smaller than the female, weighing an average of 0.5 pounds and measuring 4-5.5 inches in length. Males are often melanistic (very darkly colored), and sometimes have black markings on their upper jaw, resembling a mustache.

Females weigh an average of 1.5 pounds and measure 6-9 inches long. Adult females have wider heads and shorter tails than males.

Range of seven sub-species of diamondback terrapin. A) Malaclemys terrapin terrapin B.) M. t. centrata C.) M. t. Tequesta D.) M. t. rhizopararum E.) M. t. macrospilota F.) M. t. pileata G.) M. t. littoralis. (source: Hart 2005) Map courtesy of researchgate

Range: Diamondback terrapins have a wide distribution and may be found on the Atlantic and Gulf coasts from Cape Cod to Texas.

Habitat: Diamondback terrapins inhabit brackish and saltwater estuarine habitats including bays, rivers, sounds, tidal creeks, and coastal marine habitats. Little is known about the habitat use of juvenile terrapins although it is thought they spend much of their early life hiding under mats of decaying marsh grass. Adult terrapins are known to have very high site fidelity, often spending their entire adult life in the reaches of a single tidal creek.

Diet: Diamondback terrapins are known to primarily eat a variety of estuarine invertebrates including snails, bivalves, and small crabs, but certain plants and algae are also consumed. Fiddler crabs are particularly important food items. Terrapins also scavenge on fish and other dead marine organisms.

female diamondback_terrapin.jpg

Life History: Courtship and mating occur in April and May in open water at the confluence of tidal creeks. Females emerge from the water in late spring and summer and lay 4 to 18 pinkish white eggs (average 9), which are about 1.5 inches long, leather-like, and thin-shelled, with a blunt end. Terrapins are commonly found nesting on sandy beaches, dunes, and road or causeway embankments, and even in household gardens adjacent to a salt marsh. Females may lay several clutches each year. Maximum egg-laying activity usually occurs at high tide, ensuring that the eggs will be laid above the high water level. The females dig cavities 4 to 8 inches deep to deposit eggs. The incubation period is variable but ranges from 61 - 68 days. Hatchlings emerge from the nest in summer and early fall. The 1 to 1.25-inch hatchlings are patterned similar to the adults. Occasionally after hatching, the young may remain in the nest for the first winter, emerging in April and May to head for brackish waters.

Studies in New York indicate that females lay at least two clutches per nesting season. 

During colder winter months, terrapins may hibernate buried in mud on the creek bottom or in creek banks near the high tide line. Most terrapins become inactive by November, and begin to appear again in late Marsh and April. Female terrapins are sexually mature at approximately 5 years of age while males mature somewhat faster at 3 years of age.