SEATURTLES: Cheloniidae

PHYSICAL CHARACTERISTICS

The seaturtles are large animals that live in the ocean. Their upper shell, or carapace (KARE-a-pays), is quite flat rather than highly rounded. The lower shell, or plastron (PLAS-trun), is a bit smaller than in most turtles and attaches to the upper shell by tough but flexible tissues called ligaments (LIH-guh-ments), rather than the bony bridge common to land turtles. Seaturtles are excellent swimmers, gliding through the water with sweeps of their large, broad, and powerful front limbs, which look like flippers or paddles. Unlike many other turtles, they cannot retract, or pull back, their limbs or heads into their shells. The largest members of the family, the leatherback seaturtles, tip the scales at half a ton (454 kilograms) or more. The leatherbacks have a carapace that measures 6 to 7 feet (1.8–2.1 meters) in length.

GEOGRAPHIC RANGE

Seaturtles inhabit all the oceans of the world and the Mediterranean Sea.

HABITAT

These turtles live in saltwater from the tropics to areas with mild climates well north and south of the equator, the imaginary circle around Earth that is midway between the poles. They are more common close to shore than far out to sea, and they feed and nest at sites along the coastlines on continental shelves, or shallow plains forming the borders of continents.

DIET

Most seaturtles are primarily meat eaters. Their diets are made up of a variety of marine, or sea, animals, including fishes; snails and other mollusks (MAH-lusks), or animals with a soft, unsegmented body covered by a shell; barnacles and other crustaceans (krus-TAY-shuns), or animals with a soft, segmented body covered by a shell; and certain sponges and sea urchins. The green seaturtle is the only member of the family that is known to prefer eating plants. Sea grasses make up the majority of its diet.

BEHAVIOR AND REPRODUCTION

Perhaps the most famous behavior of seaturtles is migration (my-GRAY-shun). An individual seaturtle may travel hundreds of miles to go from its feeding area to its nesting site and back. Usually, the feeding grounds are in temperate waters, which are neither very warm nor very cold; the nesting areas, on the other hand, are in tropical waters, which are very warm. The distance between the two places can result in a trek, or journey, of 190 miles (306 kilometers) or more, one way. When the winter months arrive, many turtles migrate (MY-grayt) to warmer tropical waters, but some drop down to the muddy bottoms of coastal waters and bury themselves there to survive the coldest temperatures.

TRAWLING AND TURTLES

Trawling is a type of fishing business that many scientists believe is dangerous to marine life, including seaturtles. In this kind of fishing, a device scrapes the seafloor and collects animals that live on the bottom. For turtles, the danger is not in accidentally collecting them but rather in disturbing them as they move from feeding grounds to nesting sites. One study of olive ridley seaturtles found that trawling delayed the arrival of the female turtles at their nesting sites, and the females laid their eggs later in the year, when temperatures were warmer. The warmer temperature meant that the young ridleys were mostly females. Scientists believe that if this shift in the numbers of males and females continues, it could have an effect on the survival of this endangered species.

Female seaturtles typically produce several clutches, or nests, of eggs in a season—sometimes seven or more—but they do so only once every two or three years. Rarely, a seaturtle will nest every year. In some cases, the female turtles will gather offshore in groups. Members of these groups clamber onto shore to make nests near one another. The females of almost all species wait until nightfall to dig their nests and lay their eggs. The round eggs are leathery and range from about 1 to 2 inches (2.5–5 centimeters) in diameter, or width across each egg. A single clutch may contain up to 250 eggs, but 90–130 is more common. The eggs hatch in forty to seventy days. As with most turtles, the outdoor temperature during their incubation (ing-kyuh-BAY-shun), or the period of time before the eggs hatch, determines whether the egg will become a male or female upon hatching. When the weather is warm, more females hatch; males usually hatch when the weather is cooler.

SEA TURTLES AND PEOPLE

Humans have long sought seaturtles and seaturtle eggs as food. Some people make the eggshells into trinkets. Adult leatherback seaturtles are also prized for their skins.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists the olive ridley, loggerhead, and green seaturtles as Endangered, meaning that they face a very high risk of extinction in the wild in the near future. The hawksbill and Atlantic ridley seaturtles are Critically Endangered, meaning that they face an extremely high risk of extinction in the wild in the near future. Hunting and egg collecting, along with dangers that come from shrimping and fishing practices, are responsible for much of the decline in turtle numbers. The U.S. Fish and Wildlife Service lists the olive ridley seaturtle as Threatened, meaning that it is likely to face the danger of extinction in the near future in the United States. Certain populations of green seaturtle are Endangered, and others are Threatened. The hawksbill and Kemp's ridley are Endangered, and the loggerhead is Threatened.

GREEN SEATURTLE (Chelonia mydas): SPECIES ACCOUNTS

Physical characteristics: The green seaturtle is dark brown to black, with a whitish underside. This turtle gets its name from the color of its body fat, which is green from their diet of algae (AL-jee), or tiny, plantlike growths that live in water. The upper shell of this large turtle can measure 5 feet (1.5 meters) in length, and the turtle itself can weigh as much as 750 pounds (340 kilograms). It has large, flipper-like front legs, with which it swims, and a fairly flat upper shell, to slice more easily through the water. Compared with females, males have a long claw on the front flipper and a lengthier tail and narrower upper shell.

Geographic range: The green seaturtle lives in tropical and temperate seas around the world.

Habitat: Although they sometimes can be found in temperate saltwater areas or far out at sea, green seaturtles are much more common in shallow, sea-grass-covered coastlines and in the warmer waters of the tropics.

Diet: Adult green seaturtles spend much of the daylight hours munching on sea grasses and algae, which are the main items of their diet. Only rarely do they eat a bit of meat, such as a sponge or jellyfish. Some scientists believe that the young may eat much more meat, but there is no evidence that they do.

Behavior and reproduction: As a cold-blooded animal, or one that gets its body warmth from the surrounding environment, the seaturtle does different things to maintain a healthy body temperature, such as rising to the sunshine-drenched top of the water column. Unlike other saltwater-living turtles, this species will even crawl up on the shoreline to bask, or rest, in the sun. When winter cold arrives, some species hibernate (HIGH-bur-nayt), or become inactive, by dropping down to the bottom of the water and burying themselves in the mud. In the breeding season, when they reproduce, males and females may migrate more than 1,900 miles (3,058 kilometers) from their feeding grounds to their nesting sites. There, males try to attract the females by giving them little nips, nudges, and sniffs; the turtles mate in the water. A single female may mate with several males, and so the young in a female's clutch may have different fathers, some from matings that happened several years earlier. When she is ready to lay her eggs, the female will crawl up onto a dry coastline, dig a hole, and drop in fewer than a dozen to nearly 240 eggs, although 108 to 120 per nest is typical. She may lay two to five nests, and sometimes as many as seven, in a single season. The leathery, round eggs hatch in one to three months.

Green seaturtles and people: For centuries, humans have hunted green seaturtles for their meat and their eggs, which they eat for food.

Conservation status: The IUCN lists this species as Endangered. The U.S. Fish and Wildlife Service lists the breeding populations in Florida and the Pacific coast of Mexico as Endangered and all other populations as Threatened. Besides hunting and collecting, these turtles are in danger from the development of their nesting grounds into seafront resorts, from fishing nets that entangle them and often lead to their deaths by drowning, and from boaters who unknowingly run over them with their motor propellers. ∎

LOGGERHEAD TURTLE (Caretta caretta): SPECIES ACCOUNTS

Physical characteristics: The loggerhead turtle has a short head that is wide at the rear and rounded at the front. It is the largest seaturtle, with a carapace up to 7 feet (2.1 meters) long and a weight of half a ton (454 kilograms). It has a hard shell with a keel, or upper ridge, down the middle and large, flipper-like front limbs. The upper shell is reddish brown to greenish, and the lower shell is whitish to yellowish.

Geographic range: The loggerhead lives in tropical and temperate oceans of the world, as well as the Mediterranean Sea.

Habitat: For the breeding season, this saltwater turtle prefers tropical waters in protected areas, such as bays, or parts of the sea that cut into a coastline, and estuaries (EHS-chew-air-eez), or the wide parts at the lower ends of rivers, where the river meets the sea. The turtle travels well into temperate regions during the remainder of the year.

Diet: Meat is the primary food of both young and adult loggerheads. Hatchlings, or newly hatched turtles, will also eat pieces of the algae mats among which they float, and adults will munch on underwater plants and algae. Favored food items for adults include snails and other mollusks, sponges, squid, and fishes.

Behavior and reproduction: Females sometimes migrate every year, but usually every two to three years, from feeding areas to nesting sites, which may be 1,300 to 1,700 miles (2,092–2,736 kilometers) away. While migrating, the males court the females with little bites, and the two turtles mate while floating in the water. After mating with one or more males, the female arrives at the nesting site, waits until nightfall to crawl onshore, digs a hole, and typically lays 96 to 120 round eggs. She may lay up to seven clutches in a single season. In about two months the eggs hatch. The young from a single female—even young from the same clutch—may have more than one father. The incubation temperature determines the sex of turtles, with higher temperatures producing females and lower temperatures producing males.

Loggerhead turtles and people: Some people still hunt this turtle and collect its eggs for food.

Conservation status: The IUCN lists the loggerhead as Endangered, and the U.S. Fish and Wildlife Service describes them as Threatened. Development of coastal properties seems to be destroying their nesting areas, which has led to their decline. ∎

FOR MORE INFORMATION

Books:

Bjorndal, Karen A. Biology and Conservation of Sea Turtles. Washington, DC: Smithsonian Institution Press, 1995.

Dunbier, Sally. Sea Turtles. Hauppauge, NY: Barron's Educational Service Series, 2000.

Kalman, Bobbie. The Life Cycle of a Sea Turtle. New York: Crabtree Publishing, 2002.

Laskey, Kathryn. Interrupted Journey: Saving Endangered Sea Turtles. Cambridge, MA: Candlewick Press, 2001.

Lutz, Peter L., and John A. Musick, eds. The Biology of Sea Turtles. 2 volumes. Boca Raton, FL: CRC Press, 1996–2003.

O'Keefe, M. Timothy. Sea Turtles: The Watcher's Guide. Lakeland, FL: Larsen's Outdoor Publishing, 1995.

Web sites:

"Animal Bytes: Sea Turtles." Animals. http://www.seaworld.org/animalinfo/animalbytes/animalia/eumetazoa/coelomates/deuterostomes/chordates/craniata/reptilia/testudines/sea-turtles.htm (accessed on September 7, 2004).

"Sea Turtles for Kids." Kidz Korner. http://www.turtles.org/kids.htm (accessed on September 7, 2004).

"Turtles in Trouble." National Geographic Kids.http://www.nationalgeographic.com/ngkids/9911/turtle (accessed on September 7, 2004).