Mississippi Diamond back Terrapin
MISSISSIPPI DIAMONDBACK TERRAPIN
Photo Credit: Weeks Bay Reserve Foundation
SCIENTIFIC NAME: Malaclemys terrapin pileata (Wied)
OTHER NAMES: None.
DESCRIPTION: A medium-sized (max. length females, 230 mm [9 in.]; males 140 mm [5.5 in.]) brackish-water turtle known to frequent saline habitats. Toes webbed. Adult carapace oval, gray to nearly black, and unmarked; larger carapacial scutes with deep and obvious concentric growth rings. Midline of carapace with row of knobs or bumps, more prominent in females than males. Plastron creamy yellow with some dark spots or blotches. Head and neck smoky gray or light greenish-gray with round black spots. Top of head and limbs usually dark. Mouth consists of a sharp cutting edge and a wide grinding plate on the inner, upper surface. Females bulkier than males, with larger heads, more rounded snouts, deeper shells, and shorter tails. Carapace of juveniles rounder and lighter in color, but concentric carapacial rings darker in outline. Seven subspecies currently recognized (Ernst and Bury 1982).
DISTRIBUTION: The diamondback terrapin is distributed along coastal North America from Massachusetts to southern Texas. The Mississippi diamondback terrapin is found from the Florida Panhandle to eastern Louisiana. In Alabama, confined to the estuaries, salt marshes, and nearby shallow waters of coastal Mobile and Baldwin Counties, including Dauphin Island (Marion 1986). Size of populations and precise distribution in Alabama very poorly known.
HABITAT: A resident of coastal salt marshes, estuaries, and tidal creeks, so it is restricted to the Gulf Barrier Islands and Coastal Marshes ecoregion. Although particularly associated with cord grass marshes, it does venture from these confines, occasionally being found on offshore sandy islands or on extensive tidal mudflats. Seems to prefer marshes having open channels with moving water nearby. May bask on mud flats or float in channels; not easily captured. Will venture into brackish streams, but will not tolerate fresh water for extended periods of time. May bury in mud. Juveniles may spend first few years under mats of flotsam or vegetation (Ernst et al. 1994).
LIFE HISTORY AND ECOLOGY: Very tolerant of high temperatures, and bask frequently on mud flats or floating debris. Spend the night buried in soft mud in shallow water. Also overwinter in mud, but may emerge during periods of warm weather. Copulation takes place in the water in early spring, soon after emergence. Details of reproduction of this particular subspecies not well known, but presumably similar to those of other subspecies (Seigel 1979). From two to five clutches laid by each female per season, beginning in April or early May. From five to 12 oblong, pinkish-white and thin-shelled eggs deposited each time in nests dug on beaches or sand dunes above the high-tide mark. Incubation takes 10 to 12 weeks, and young may overwinter in nest. Many nests destroyed by raccoons, fish crows, gulls, and other predators. Hatchlings often fall prey to large wading birds. Sexual maturity probably reached in three to four years in males, six or seven years in females. Maximum egg production occurs at about 25 years. Upper age limit may exceed 40 years. Large muscular jaws are well adapted to crush and eat hard-shelled prey such as molluscs and crustaceans. Primary food items include snails, clams, and crabs. Other prey items include carrion, fishes, marine annelids, and plant material. Feeding occurs mainly at high tide when turtles cruise the flooded marshes for snails found on cord grass stems and can forage easily along the bottom for small crabs and other invertebrates. Feed on tender shoots and rootlets of marsh plants and may wander a few meters (several feet) into grassy lowlands during high tide in search of insects.
BASIS FOR STATUS CLASSIFICATION: Rare in the coastal brackish marshes of Mobile and Baldwin Counties. Faces a growing series of environmental perils in Alabama. The major threat has been, and continues to be, the reduction of marsh habitat along the Alabama coast as a result of dredging and filling operations associated with real estate and industrial development. Activities of the Tennessee-Tombigbee Waterway and the eventual development of Alabama’s natural gas and petroleum resources may continue to reduce the amount of suitable marsh habitat that is available. Industrial expansion in the Mobile area may increase the pollutant load in the Bay and surrounding estuaries. During the last several decades, some natural losses of marsh habitat have occurred repeatedly. The Gulf Coast is subject to hurricanes every few years that wash away particularly favorable habitats on Dauphin Island and the mainland. Recent preliminary trapping programs conducted at Weeks Bay and at Dauphin Island have revealed very few terrapins. Routine field excursions disclose that sightings of specimens along coastal Alabama are progressively uncommon or rare (Mount 1975). Although the historically extensive hunting of the diamondback terrapin for food along the coast of North America has subsided, and some populations may have begun to recover, a small number of people along the Alabama coast persist in procuring them for food (Carr 1952). Also, increasing numbers of crab traps are placed close to marsh areas, resulting in the inadvertent capture and drowning of the turtles. This may help to explain the authors’ assessment that large females are now very rare in many areas of apparently suitable habitat along the Alabama coast. Although there remain some areas where the Mississippi diamondback terrapin can be seen in Alabama, it is apparent that its numbers have sharply declined in recent years and that more serious declines can be anticipated in the future if its welfare and that of its habitats are neglected.
Authors: David H. Nelson and Ken R. Marion