Diamondback terrapins are turtles with concentric, diamond-shaped markings and grooves on the scutes (plates) of their carapaces (top shells), which range from medium gray or brown to nearly black.
Their skin color is a pale to dark gray or black, flecked with dark spots, blotches or stripes. The hingeless plastron (bottom shell) is yellow to green or black and may be marked with dark blotches. No two individual diamondback terrapins are exactly alike in coloration and pattern.
Their feet are strongly webbed; the hind feet are especially large and flat. These large webbed feet and muscular legs make terrapins strong swimmers, a necessary ability when living in an environment with daily tidal changes and strong currents.
Mating takes place in the early spring, with nesting extending through mid-summer. Females lay two to three clutches of eggs annually, with clutch sizes ranging from four to 23 eggs.
During the cold winter months, diamondbacks hibernate, buried in the mud at the bottom of tidal creeks. In the northern part of their range, terrapins enter hibernation in November or December and emerge between April and May. Hibernating terrapins remain completely submerged and inactive throughout the winter. Oxygen needs are greatly reduced due to low metabolism and inactivity during this dormant state. Dissolved oxygen is also absorbed from the water through the mouth and tail opening (the cloaca).
Diamondbacks are well adapted for eating hard-shelled prey, including aquatic snails, crabs and small bivalves, such as blue mussels and clams. Females have broad plates on their jaws to help crush prey. Terrapins also eat carrion, fish, marine worms and insects. They are almost strictly carnivorous but sometimes ingest small amounts of plant material while eating other prey.
Adult males are significantly smaller than females in weight and carapace length. Males reach a maximum shell length of 5.5 inches, while females can grow up to 11 inches. Females also have wider heads, deeper (taller) shells and shorter tails than males.
Diamondbacks live in coastal salt marshes, estuaries and tidal creeks along the U.S. Atlantic and Gulf coasts from Cape Cod, Mass., to Corpus Christi, Texas, including the Florida Keys. Seven subspecies occupy this range, with some overlap in distribution. The northern diamondback exhibited at the Aquarium inhabits a range from Cape Cod, Mass., to Cape Hatteras, N.C.
Diamondback terrapin populations have declined considerably in many parts of their geographic range and are listed as endangered, threatened or species of special concern in some states. The current status of the northern diamondback population throughout the Chesapeake and coastal bays is unknown. The species is currently classified as “apparently secure” by both Maryland and Virginia
Terrapin populations fell to dangerously low levels in the 20th century after a long period of large-scale harvesting for their meat. Commercial harvest of terrapins ended in Maryland in 2007. Other factors causing declines in terrapin populations include the loss of salt marsh habitat and destruction of nesting beaches due to waterfront development, road mortalities of nesting females, boat strikes, excessive predation by raccoons and continued commercial harvesting in a few states.
Terrapins are attracted to the same bait used to lure blue crabs. When trapped in submerged crab pots or commercial fishing gear, air-breathing terrapins will eventually drown. The loss of adult terrapins in crab pots is believed to be a main cause of population declines in many parts of their range.
Almost all deaths in crab pots could be prevented by equipping these traps with turtle excluders, or “bycatch reduction devices” (BRDs). This simple modification still allows large crabs to enter but keeps adult terrapins out. Maryland crabbing regulations require that all recreational crab pots (waterfront property owners are allowed two) be equipped with BRDs.
The Maryland Department of Natural Resources provides information on how to make excluders, and the devices can also be purchased at many bait shops.
Nesting terrapin females are vulnerable to predation by raccoons. Eggs and hatchlings are preyed upon by a wide variety of animals including crabs, crows, gulls, herons, rats, muskrats, foxes, raccoons, skunks and mink. Terrapin eggs are also destroyed by the invasion of introduced beach grass and common reed. Survival rates of nests and hatchlings are very low due to high predation and flooding.
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