Leatherback Seaturtle: Dermochelyidae

views updated

LEATHERBACK SEATURTLE: Dermochelyidae

PHYSICAL CHARACTERISTICS

The leatherback seaturtle, which is the only member of its family, is extremely large. The carapace (KARE-a-pays), or upper shell, measures up to 8 feet (2.4 meters) long, and the turtle itself weighs just under a ton, at 1,911 pounds (867 kilograms). Most seaturtles have a hard and bony upper shell, but this turtle's carapace has a smooth, leathery skin. It also has an unusual outline. The upper shell is wide at the front but then narrows to a point at the back, giving it a teardrop shape. In addition, seven very noticeable ridges run from the front of the carapace to the back. This shell is usually black with a few white or yellow spots— almost as if someone had shaken a paintbrush over the back of the turtle. The plastron (PLAS-trun), or bottom shell, has coloring that is the opposite of the carapace coloring. Instead of black with light spots, it is white with dark spots. Leatherback turtles also have large front legs, which do not have separate toes and claws but instead look like paddles or fins.

GEOGRAPHIC RANGE

This species lives in oceans around the world.

HABITAT

The leatherback seaturtle is found over more of the world than perhaps any other species of reptile. It can live quite well in the warm ocean waters of the tropics and in cooler ocean waters as far north of the equator as Alaska and Iceland and as far south as New Zealand and the Cape of Good Hope at the southern tip of Africa. It rarely comes into shallow, shoreline waters, staying instead in deeper water for most of its life.

DIET

The diet of the leatherback seaturtle is mostly jellyfish. It also eats many other ocean-living animals, including snails, octopuses, squids, crabs, small fishes, and hydrozoans (hy-druh-ZOH-uhns). Hydrozoans and jellyfish are both sea-dwelling animals without a backbone that have tentacles (TEN-tih-kuhls), or long, thin body parts used for feeling or for holding on to things. These two types of animals look somewhat alike. Seaturtles sometimes think that floating balloons and plastic bags look much like these creatures too, and they eat them by mistake. This can kill the turtle. The turtles also eat plants, such as sea grasses and kelp, which is a type of seaweed.

SAVING LEATHERBACKS

Leatherback seaturtles have survived on Earth for at least 100 million years. They have even outlasted the great dinosaurs, yet they are now facing extinction. The number of female leatherbacks worldwide dropped from 115,000 in 1982 to fewer than 25,000 two decades later, and the turtles living in the Pacific Ocean suffered the biggest decline in numbers. Many conservation groups, as well as country governments, are worried about the future of this turtle and are trying to do away with hunting and egg collecting. They are also preserving their nesting beaches and protecting adult turtles from fishing and other activities at sea that accidentally harm the turtles.

BEHAVIOR AND REPRODUCTION

Like other turtles, the leatherback seaturtle is cold-blooded, meaning that its body temperature gets cooler when the outside temperature drops and warmer when the outside temperature rises. In most turtles, body temperature very closely matches the outdoor temperature. The seaturtles are a little different. Because they are so large and their muscles heat up when they swim, they can stay warm much longer than a smaller turtle can. They also have oily skin that acts like a jacket, to help keep the body warm. For these reasons, they are able to travel to much colder waters, like those off Alaska or Iceland. These turtles take advantage of this ability to travel to warm and cold waters. They often swim very long distances in what are called migrations (my-GRAY-shuns), moving from one region or climate to another to find food and to lay their eggs. Scientists have tracked some turtles that have swum as far as 3,100 miles (4,989 kilometers) one way to go from a nesting site to a feeding site. On average, these turtles swim about 19 miles (30.5 kilometers) a day for weeks at a time.

Many leatherback seaturtles may join together at a particularly good feeding site, like a school, or group, of jellyfish. They also hunt for food alone. Seaturtles are excellent divers, and they can swim down to more than 3,300 feet (1,006 meters) to find deep-water animals to eat. Turtles do most of their diving at night, but they are active both day and night.

Scientists know very little about courtship or mating in leatherback turtles. The turtles may mate before or during the long migration from a feeding area to a nesting area or just offshore from the nesting site. Females make their nests about once every three or four years on tropical beaches. Those that live in the Atlantic Ocean nest from April to November. Pacific Ocean leatherbacks nest at different times of the year, depending on the beach they choose. A small group of females usually nests together on one beach.

The females climb up onto shore, usually at night, and find a spot on dry land. They typically pick a nesting site that is just beyond the highest point that water reaches. Like the upper shell, the lower shell of leatherbacks is softer than that of most turtles, so the females choose sandy rather than rocky beaches to crawl over and dig their nests. They use both their front and back legs to dig a wide hole that can fit the entire body. Then they continue to dig a smaller, deeper pit with just the rear legs. Each female lays 47 to 263 eggs in the pit. Only some of the eggs hatch. From the time she lays them, 1 to 103 eggs have no yolks and so cannot develop into turtles. The rest are normal eggs. Eggs are round and range in diameter, or width, from 1.9 to 2.6 inches (4.8 to 6.6 centimeters) in diameter. Each egg weighs 2.5 to 3.2 ounces (71 to 91 grams).

Usually, the biggest females lay the most eggs and the largest eggs. In addition, turtles of the Atlantic typically lay more eggs than those of the Pacific, and nests made during the middle of the nesting season often contain more eggs than nests made earlier or later. Females may make up to eleven nests a year, although five or six is more common. Once she lays the eggs, the female uses her hind legs to cover them with sand and then continues with her front and rear legs to bury the larger body hole. She then leaves the area and provides no care for the eggs or the newly hatched young.

The eggs hatch in sixty to sixty-eight days, although some may hatch in as little as fifty days or as much as seventy-eight days. If the beach, and therefore the nest, is especially warm about halfway through the eggs' development, most of the eggs hatch into females. If the nest is particularly cool, most of the eggs will hatch into males. The hatchlings wait until nightfall to climb out of the nest and onto the surface of the beach. They then head to the area that is most open to the sky and is the most brightly lit—usually the ocean. The young turtles continue to grow at sea, and when the reach the age of thirteen to fourteen years, they are ready to become parents themselves.

LEATHERBACK SEATURTLES AND PEOPLE

Because this turtle is found in so many areas of the world, it has many names. In Trinidad, for example, people call it caldon, while in the Caribbean and Latin America the turtle is known as canal. This familiarity can pose a problem, however. Although it is illegal in most countries, some people continue to raid the turtles' nests for their eggs or hunt them for their meat or the oil in their shells.

CONSERVATION STATUS

According to the World Conservation Union (IUCN), this species is Critically Endangered, which means it faces an extremely high risk of extinction in the wild. The U.S. Fish and Wildlife Service lists the leatherback turtle as Endangered, meaning that the turtle is in danger of extinction through all or most of its range, or the region over which it roams and feeds. The number of leatherback turtles has dropped rapidly over a very short time, mostly due to hunting of adults and gathering of their eggs. Development of tropical beaches for homes and resorts is also making it more and more difficult for the turtles to find a safe nesting spot. Many countries are now making it illegal to kill adult turtles or take their eggs or else protecting the beaches where they lay their eggs.