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New Jersey Endangered and Threatened Species Field Guide
Atlantic green turtle
Species Group: Reptile
The green turtle is a large sea turtle with a low, broadly oval carapace and small head with one pair of pre-frontal scales that are unique to green turtles. Adult shell length ranges from 36-43 inches and weights average between 200-300 pounds. Single-clawed flippers are paddle-shaped. Color varies widely. Adults have a smooth carapace that ranges from pale to very dark and from plain colors to brilliant mixtures of yellows, browns and yellows that radiate in stripes or are splattered with dark splotches. The plastron is whitish to light yellow. The upper surface of the head is light brown with yellow markings; sides of the head are brown with broad yellow margins. The neck is dusky above and yellow near the shell below. The tail and flippers are colored like the carapace and plastron.
Hatchlings are dark brown or nearly black on the upper side, with white plastrons and white margins on the shell and limbs. In juveniles, the carapace has radiant patterning similar to hawksbill sea turtles, and the scales of the head and upper side of the flippers are fringed by a narrow, clear yellowish margin.
Distribution and Habitat
Unlike land turtles from which they evolved more than 150 million years ago, sea turtles spend almost their entire lives in the sea. When active, they often come to the surface to breathe, but can remain underwater for several hours at a time while resting.
Though most sea turtles inhabit warm, tropical and subtropical waters, they migrate northward as water temperatures increase in the late spring and summer and remain in northern waters until late fall. From late May until November, New Jersey coastal waters provide important seasonal foraging habitat.
Green turtles occur within the warmer portions of the Atlantic, Indian, and Pacific oceans, as well as the Mediterranean and Caribbean seas. Within the Atlantic Ocean, they may be found from northern Argentina to southeastern Canada. In the U.S. Atlantic and Gulf of Mexico waters, they can be found from Texas to Massachusetts, as well as around Puerto Rico and the U.S. Virgin Islands. They are typically found in inshore and nearshore waters.
Green turtles primarily use three types of habitat: ocean beaches (for nesting), the open ocean, and shallow feeding grounds in coastal areas. Nesting occurs in subtropical and tropical regions on open sandy beaches above the high-tide mark in front of well-developed sand dunes. Nesting in the U.S. is mainly within Florida and Hawaii. They do not nest as far north as New Jersey.
After emerging from the nest, hatchlings make their way to the relative safety of the ocean. They then swim to offshore areas, where they are believed to live for several years feeding near the surface on a variety of small plants and animals. Once they reach a certain age or size, they’ll travel to foraging grounds in coastal areas where sea grasses and algae are available.
Adult green turtles are largely herbivores, feeding primarily on marine algae and marine grasses. The adults are the only sea turtles which feed exclusively on plants. Juvenile green sea turtles may eat both invertebrates and aquatic vegetation such as eelgrass, which grows in beds in Barnegat Bay.
It is estimated that green turtles reach sexual maturity between 20-50 years of age, after which time females will return to the beaches where they were born in order to lay their eggs. Green turtles begin mating in late March. Nesting occurs between May and early September, but peaks in June and July. Females lay an average of 5 clutches of about 135 eggs at intervals of about 2 weeks, every 2-4 years. They nest primarily at night, often at high tide. Eggs hatch in about 2 months. Egg mortality may result from predation, beach erosion, invasion of clutches by plant roots, crushing by off-road vehicles, or flooding by sea water or excessive rainfall. The gender of hatchlings is affected by incubation temperature, with warmer temperatures resulting in a higher number of females and cooler temperatures producing mainly males. Hatchlings emerge from the nest a few days after hatching, typically during darkness. Of every thousand hatchlings, only a few are believed to survive to adulthood. Once they reach water, male hatchlings will never return to land while females will only do so to nest.
Green turtles are found in New Jersey waters typically between summer and fall, when water temperatures are warmer. When water temperatures begin to drop, they must migrate south or risk dying or becoming “cold-stunned”. “Cold-stunning” occurs when sea turtles become immobile due to the dramatic decrease in water temperature (usually below 50°F) making it impossible for them to escape the cold water and migrate to warmer water. A cold-stunned sea turtle may appear to be dead, but may actually be alive. Without proper intervention a cold-stunned sea turtle will inevitably die.
Scientists believe that green turtles may live to 100 years in age. Aside from humans, the only predator of adult green turtles is large sharks. Hatchlings may be preyed upon as soon as they leave their nest by raccoons, crabs, and birds. Once in the ocean, hatchlings may also be preyed upon by large fish.
Current Threats, Status, and Conservation
Green turtle populations have been decimated by overharvesting of adults and eggs, loss of nesting habitat, interactions with fisheries, and entanglement or ingestion of marine debris. Their populations are currently a small fraction of their historical size. Because of this, green turtles from the Florida and the east Pacific breeding populations were listed as federally endangered and those from other parts of the globe were listed as threatened in 1978. The green turtle was listed as threatened by the state of New Jersey in 1979. In 2016, the New Jersey Endangered and Nongame Advisory Committee recommended an Endangered status for this species within the state, but no formal rule proposal has been filed to date.
Green turtles are currently faced with many threats such as the direct exploitation for food (including eggs), entanglement in fishing gear, oil spills, habitat degradation (such as beach development), beachfront lighting, ocean pollution (including marine debris, which may be ingested), and dredging (direct kills and injuries). Beach cleaning operations can destroy nests or produce tire ruts that inhibit movement of hatchlings to sea. Additional threats include predation and trampling of eggs and young by raccoons and feral mammals, crushing of eggs or young by vehicles or humans, collisions with boats and intentional attacks by fishermen. Long-term threats include sea level rise which, coupled with inland urbanization, may reduce available nesting beaches. Since sexual differentiation depends on incubation temperature, there is concern that global warming may result in an imbalance in the sex ratio.
Green turtles are also threatened, in some parts of the world, by the disease fibropapillomatosis which causes tumors to grow on their skin. The tumors are not necessarily deadly to the animal unless they begin to block the sight, breathing, or feeding of the turtle. It is not currently known what the cause of the disease is, but it appears to occur more commonly in areas impacted by human activities.
Habitat use of sea turtles within New Jersey waters is poorly understood. The degree to which New Jersey plays a critical function in providing foraging habitat and migration corridors is unknown. Surveys are currently being conducted off the New Jersey coastline in order to determine where sea turtles are located, how many individuals are there, and during what time of year. Based on these findings, further knowledge regarding their habitat use in New Jersey waters may be gained and attention may then focus on protecting important habitats.
Text derived from the book, Endangered and Threatened Wildlife of New Jersey. 2003. Originally edited by Bruce E. Beans and Larry Niles. Edited and updated Michael J. Davenport in 2010 and 2016.
Species: C. mydas
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