Green Turtle

Habitat

This marine turtle migrates along routes crossing between tropical and subtropical waters; occasionally it will venture into cooler northern waters. The turtle requires tropical beaches for nesting.

Range
With Atlantic and Pacific Ocean populations and multiple migratory tracts, the green turtle is found in open water and along the coasts of many countries (while widespread, the turtle’s numbers are still in danger). Its range includes the waters between Papua New Guinea, the Galapagos and Hawaiian islands, Mexico, Panama, Colombia, Venezuela, Chile, Argentina, South Africa, and New Zealand. It may stray as far north as Alaska, Canada, Europe, or Japan.

National Parks
Tortuguero National Park (June through October or November).

Physical Description
The large, brown marine reptile was named the green turtle because its body fat has a greenish hue. The underside of the turtle (the plastron) is a yellowish white or cream color. The exposed body parts have grayish skin. The wide, heart-shaped shell (carapace) may have some olive or dark colorings and wavy line markings. Juveniles look different: the shell is a darker blue-black and the underside is a brighter white with a dark band down each side of the body.

Males have one claw at the end of each front flipper as well as a long tail that reaches beyond the shell edge; these help him hold onto the female during mating. A female’s tail is shorter and does not extend past the edge of her shell.

This turtle sometimes resembles the hawksbill turtle; counting scales or scutes can help distinguish these two, but more simply Chelonia mydas has an elongate, rounded head that is not narrow like the hawksbill and does not end in a hooked bill. The green turtle’s Atlantic Ocean presence carries a separate migration route from the populations in the Pacific Ocean. Those in the Pacific tend to be smaller and darker.

Biology and Natural History
Every 2 to 4 years, a female green turtle will join the large offshore aggregations of adults who come to breed. In the shallow waters, males and females approach each other and the male fixes himself above the female by holding on with his hooked front flippers and prehensile tail. Some aggressive males may try to dislodge another male from his position, and occasionally two or even three males will clamor in an awkward stack on top of one female.

After mating, a female may come onshore once every few days to lay another clutch of eggs; she may make up to 7 of these trips, although most only do so 2 or 3 times. In Costa Rica they tend to return to the same location each time they breed. She will use her front flippers to scoop out a deep hole, then carefully deposit about 100 fragile, leathery-shelled eggs resembling ping pong balls, and finally covers the eggs in sand. Turtles develop according to temperature-dependent sex determination. This means that if the temperature of the egg is lower than 28.5oC, that turtle will become a male; if the temperature is greater than 30.3oC, it will be a female. That is, if the turtle makes it to hatching. Humans, dogs, raccoons, and other animals dig up nests. After several weeks the eggs hatch into tiny turtles which scramble to the surface and towards the ocean. Gulls, frigatebirds, and crabs ambush the turtles as they cross the expanse of beach to the water, where predatory fish wait for the new arrivals. However, while clumsy and slow on land, green turtles are nimble swimmers and seem to take on a different body underwater.

The first year of the green turtle’s life is not well understood. They are vulnerable in this smaller stage and eaten by many predators. The sea turtle’s main protection is hefty size and hearty shell—and infant turtles have neither yet. Few survive their first year. They may spend this time among sargassum rafts in the ocean until they reach about 0.5 kg in weight, when they return to shallower waters to feed and continue growing. Once a turtle weighs about 40 kg, it begins eating and spending more of its daily energy around floating grass flats. At 10 to 15 years of age and a mature size of 60 kg, a green turtle will begin its breeding pattern and continue for the rest of its life. At this size, the turtle is not vulnerable. Its only natural predators are large sharks.

Key aspects of the green turtle’s life cycle are still largely mysterious. Their migration patterns and behavior are difficult to trace and interpret, as are factors of sexual maturity, courtship, and ecology, making it harder for biologists to devise ways to help these vanishing sea giants. Like most marine turtles, the green turtle has suffered heavy losses from poaching for eggs, meat, and shell souvenirs. Nets of commercial shrimp fishermen and others drown pregnant females. Rising climate due to global warming is affecting sensitive egg development. Ever popular beachfront development continues to spread on and destroy fragile beach nesting sites and contribute light and noise pollution which can scare off or confuse nesting females and new hatchlings.

Tours to nesting sites are popular; some are legitimate and careful. It is important to strictly follow behavioral requirements when visiting turtle nesting beaches, particularly being quiet and not using any lights or camera flashes. Eating turtle eggs or meat dishes or buying souvenirs or products made from turtles is directly harmful to the existence of the species and unethical. Sea turtles naturally have a low survival rate and take many years to reach sexual maturity. Continuing to add human pressures to their populations may prove fatal to these graceful mysteries. Preserving their beaches and respecting their space both on land and in water is necessary for their survival.

Diet
Young green turtles are predatory, but mature ones are herbivorous, mainly grazing on shallow water sea grass pastures. Turtle grass (Thalassia testudinum) is the main course, but the turtle will consume other sea grasses or algae at times.

Height/Weight
Adults weigh 100-200 kg but can reach over 300 kg. Carapace (shell) length is usually between 90 and 150 cm long and can be over 1 m wide.

Taxonomy
Order: Testudines
Family: Cheloniidae

Sources
Carr, A. in: Janzen, Daniel H. Costa Rican Natural History. Chicago: University of Chicago Press, 1983.

Leenders, Twan. A Guide to Amphibians and Reptiles of Costa Rica. Zona Tropical, S.A, Miami, FL, 2001.

Savage, Jay M. The Amphibians and Reptiles of Costa Rica: A Herpetofauna between two Continents, between Two Seas. The University of Chicago Press, Chicago, 2002.

-Amy Strieter, Wildlife Writer