Turtle, green sea

Chelonia mydas

phylum: Chordata

class: Reptilia

order: Testudines

family: Cheloniidae

status: Endangered, IUCN Endangered and Threatened, ESA

range: Oceanic

Description and biology

The green sea turtle is the largest of the hard-shelled sea turtles. An average adult weighs 300 to 350 pounds (136 to 159 kilograms) and has an upper shell, or carapace (pronounced KAR-a-pace), length of about 40 inches (102 centimeters). The large, heart-shaped carapace varies in color from dark greenish-brown to olive brown. The turtle's head is small and its front legs are large and flipper-shaped. It feeds mainly on sea grasses and algae.

Green sea turtles build nests on beaches at various times during the year depending on their location. Mating usually occurs in the water within 0.5 mile (0.8 kilometer) of the nesting beach. After mating, the female crawls slowly up on the beach at night, being very sensitive to light, sound, and other disturbances. Using her rear flippers to dig a hole, she lays her eggs, buries them with sand, then returns to the ocean. The average clutch (eggs produced at one time) size is 110 eggs,

and a female may lay between 3 and 7 clutches a season. The eggs incubate (develop) for a period of 52 to 61 days. Upon hatching, the young turtles race for the water, but are often preyed on by birds. In the water, they are preyed on by fish.

Habitat and current distribution

The green sea turtle ranges widely, having been observed as far south as Polla Island, Chile, and as far north as the English Channel. However, it is mainly a pantropical species, meaning it nests in tropical and subtropical regions. Biologists (people who study living organisms) believe there are about 150 nesting sites worldwide. Only about 10 to 15 of these sites support large populations (2,000 or more nesting females per year). The largest sites are found on Ascension Island in the southern Atlantic, western Australia, Costa Rica, Europa and Tromelin Islands in the Mozambique Channel (strait between Madagascar and Mozambique), the Pacific coast of Mexico, the northeast coast of Oman, Pakistan, and Florida.

Because males do not leave the water, biologists have found it difficult to obtain accurate population totals for the green sea turtle. Some sources list the turtles' world population at 500,000. The breeding populations along the Pacific coast of Mexico and in Florida are the ones considered endangered. Biologists estimate that only about 300 to 400 adult females nest in Florida.

History and conservation measures

Green sea turtles have been declining in number for hundreds of years. They have always been hunted for food. In modern times, this hunting has risen with advancements in fishing technology and increases in human populations in tropical areas. Turtle eggs are collected for food; young turtles are hunted and then stuffed for souvenirs; and adults are hunted for their meat (for food), for their skins (for leather goods), and for their oil (for cosmetics).

Like other sea turtles, the green sea turtle faces the threat of nesting habitat loss. Beachfront development has decreased suitable nesting habitat for the turtle throughout its range. Even development near nesting beaches has hurt the turtle: increased shoreside lighting interferes with a female's ability to lay eggs.

Green sea turtles are often caught in shrimp nets and drown. A device called a turtle excluder device, or TED, is often used to prevent these unwanted trappings. The TED, an open-ended grid of bars, is fitted in the neck of a shrimp net. It allows small sea animals like shrimp to pass through into the bag end of the net, but prevents larger sea animals like turtles from entering. The larger animals are ejected back into open water. Although TEDs are successful in saving large sea animals, fishermen do not like to use them because they believe the TEDs limit the amount of shrimp they catch.

Because green sea turtles range across such a wide area, international cooperation is needed to conserve the species and its habitat. Agreements on how best to do that have not yet been reached.