Diamondback Terrapin (Malaclemys terrapin)

Photos by J.D. Willson unless otherwise noted

Description: The Diamondback Terrapin (Malaclemys terrapin) ranges from 5-10 inches (12.7-25.4 cm) in carapace length. Terrapins are sexually dimorphic, with males being much smaller (5-6 in), while females are considerably larger (9 in) as adults. There are currently seven subspecies of diamondback terrapin recognized throughout it’s large range. The diamondback terrapin’s carapace color varies from a brown-ebony to a darker, almost black. On the carapace, each scute has multiple “diamond-shaped” rings which may be the origin of this species’ name. The turtle’s skin can range anywhere from dark gray to stark white, which is complimented with black irregular spots. Males are often melanistic (very darkly colored), and sometimes have black markings on their upper jaw, resembling a mustache.

Habitat: Diamondback terrapins can be found along the Eastern Coast of the U.S., from Cape Cod (Massachusetts) to Texas. They are most common in salt marshes and shallow bays. They are usually found in brackish water and occasionally travel out into the open ocean, however, they cannot tolerate full-strength salty water for long periods of time, or they may dehydrate.

Habits: Diamondback terrapins reach sexual maturity at about 3.5 years in males and 6 years in females. They breed during the months of March and April and nest during May and June. There have been reports of large groups of terrapins congregating in bays to mate in the early spring. Although diamondback terrapins are an aquatic turtle and spend the majority of their life in water, they do leave the water to bask and lay eggs, like many other species of aquatic turtles. One biological advantage these turtles have acquired over time is the ability to survive in salt waters of variable salinities. Like sea turtles, diamondback terrapins posses salt glands around their eyes, allowing them to secrete excess salt from their blood, and survive in salty environments.

Conservation Status: Terrapins have a long history of exploitation by humans. For decades they were harvested for food and were often eaten in turtle soup. Although terrapins are no longer harvested in most areas, they often enter crab traps and drown. Additionally, degradation of salt marshes and nesting beaches, and road mortality of nesting females also hurt this species. Although terrapins have declined greatly in the Northeast and parts of Florida, they are still fairly common in our region and are currently listed as a non-threatened species, although it has been considered a status review species for over a decade.

Pertinent References:
Dr. Whit Gibbons at the Savannah River Ecology Lab is conducting the longest-running study of Diamondback Terrapins. Over 25 years Dr. Gibbons and other members of the SREL herpetology lab have made over 3500 captures of about 1500 individual terrapins in several salt marsh creeks at Kiawah Island, South Carolina. His research has shed light on Terrapin population dynamics and has demonstrated that the Kiawah population is declining due to mortality in crab traps.

Hoyle, M.E., and Gibbons, J.W. 2000. Use of a marked population of diamondback terrapins (Malaclemys terrapin) to determine impacts of recreational crab pots. Chelon. Conserv. Biol. 3: 129-133.

Gibbons, J.W., Lovich, J.E., Tucker, A.D., FitzSimmons, N.N, and Greene, J.L. 2001. Demographic and ecological factors affecting conservation and management of the diamondback terrapin (Malaclemys terrapin). Chelon. Conserv. Biol. 4: 66-74.

Tucker, A.D., FitzSimmons, N.N., and Gibbons, J.W. 1995. Resource partitioning by the estuarine turtle, Malaclemys terrapin: trophic, spatial and temporal foraging constraints. Herpetologica, 51: 167-181.

Tucker, A.D., J.W. Gibbons, and J.L. Greene. 2001. Estimates of adult survival and migration for diamondback terrapins: conservation insight from local extirpation within a metapopulation. Canadian Journal of Zoology 79:2199-2209.

Dorcas, M. E., J. D. Willson, and J. W. Gibbons. 2007. Crab trapping causes population decline and demographic changes in diamondback terrapins over two decades. Biological Conservation 137:334-340.

Account Author: Andrew M. Grosse, University of Georgia – edited by J.D. Willson