Diamondback turtles have 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 in the subspecies exhibited at the Aquarium.
Skin color ranges from 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 figures and blotches.
Diamondback terrapins are among the most variable turtle species in North America and no two individuals are exactly alike in coloration and pattern.
The feet are strongly webbed; the hind feet are especially large and flat. These large webbed feet and muscular legs enable terrapins to be strong swimmers, an ability needed 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. Clutch size ranges from four to 23 eggs, and varies throughout the terrapin’s range.
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 absorbed from the water in the mouth and tail opening (the cloaca).
Diamondbacks are well adapted for eating hard-shelled prey including aquatic snails (e.g., periwinkles and mud snails), crabs, and small bivalves (e.g., blue mussels and clams). Females have broad plates on their jaws to help in crushing their prey. Terrapins also eat carrion, fish, marine worms, and insects. Terrapins are almost strictly carnivorous, although a small amount of plant material is sometimes accidently ingested while eating other prey.
Adult males are significantly smaller than females in weight and carapace length. Males can reach a maximum shell length of 5.5 inches, and 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.
This range is occupied by seven subspecies with some overlap in their distribution. The subspecies exhibited at the Aquarium, the northern diamondback (malaclemys terrapin), ranges 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 for meat in a few states.
Terrapins are attracted to the same baits used to lure blue crabs in both commercial and recreational crab pots. Air-breathing terrapins will eventually drown in a submerged crab pot or other commercial fishing gear. 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 easy modification of crab pots allows large crabs to enter and 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. These simple 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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