The Diamondback terrapin is a species of turtle native to the eastern and southern United States and in Bermuda. The common name of these turtles refers to the diamond pattern on top of their shell (carapace), but the overall pattern and coloration vary greatly. The shell is usually wider at the back than in the front, and from above it appears wedge-shaped. The shell coloring can vary from brown to grey, and their body color can be grey, brown, yellow, or white. All have a unique pattern of wiggly, black markings or spots on their body and head. Diamondback terrapins have large webbed feet are very strong swimmers.
Diamondback terrapins live in the very narrow strip of brackish coastal waters on the Atlantic and Gulf coasts of the United States, from as far north as Cape Cod, Massachusetts, to the southern tip of Florida and around the Gulf Coast to Texas. A small breeding subpopulation is also found in the Bermuda Islands. In most of their range terrapins live in Spartina marshes that are flooded at high tide, but in Florida, they also live in mangrove swamps. Other habitats include estuaries, lagoons, and tidal creeks.
Diamondback terrapins are social creatures and are often seen basking together during the day. At night they rest in their burrows in the mud at low tide. These turtles spend the majority of their life in water, however, they do leave the water to bask and lay eggs. Adult Diamondback terrapins hibernate in the colder months in most of their range, in the mud of creeks and marshes.
Little is known about the mating system in Diamondback terrapins. Their breeding season occurs in May and June. Females may wander considerable distances on land before nesting. Nests are usually laid in sand dunes or scrub vegetation near the ocean in June and July, but nesting may start as early as late April in Florida. Females will quickly abandon a nest attempt if they are disturbed while nesting. Clutch sizes vary latitudinally, with average clutch sizes 5-10 eggs. After covering the nest, females quickly return to the ocean and do not return except to nest again. Like many turtles, terrapins have temperature-dependent sex determination, meaning that the gender of hatchlings is the result of incubation temperature. The eggs usually hatch in 60-85 days, depending on the temperature and the depth of the nest. Hatchlings usually emerge from the nest in August and September but may overwinter in the nest after hatching. They sometimes stay on land in the nesting areas in both fall and spring. Hatchling terrapins are freeze tolerant and may overwinter on land. Young females usually become reproductively mature at around 7 years of age; males reach reproductive maturity before females because of their smaller adult size.
In the 1900s, Diamondback terrapins were once considered a delicacy to eat and were hunted almost to extinction. The major threats to these turtles are all associated with humans. People tend to build their cities on ocean coasts near the mouths of large rivers and in doing so they have destroyed many of the huge marshes that terrapins inhabited. Traps used to catch crabs, both commercially and privately, have commonly caught and drowned many Diamondback terrapins, which can result in male-biased populations, local population declines, and even extinctions. When these traps are lost or abandoned (“ghost traps”), they can kill terrapins for many years. Nests, hatchlings, and sometimes adults are commonly eaten by raccoons, foxes, rats and many species of birds, especially crows and gulls. The density of these predators are often increased because of their association with humans. Terrapins are also killed by cars when nesting females cross roads and mortality can be high enough to seriously impact populations. These turtles are still harvested for food in some states. Terrapins also suffer from pollutants such as metals and organic compounds and are collected for the pet trade. Some people breed the species in captivity and some color variants are considered especially desirable.
According to the IUCN Red List, the total population size of the Diamondback terrapin is unknown. However, there is an estimated populations of the species consisting of 100 individuals in the Bermuda Islands. Currently, Diamondback terrapins are classified as Vulnerable (VU) on the IUCN Red List and their numbers today are decreasing.
Due to feeding upon aquatic organisms, Diamondback terrapins control the numbers of these species’ populations throughout the area of their habitat.