leatherback n : wide ranging marine turtle with flexible leathery carapace; largest living turtle [syn: leatherback turtle, leathery turtle, Dermochelys coriacea]

English

Noun

1. A large sea turtle, Dermochelys coriacea, with a leathery back.

Translations

The leatherback turtle (Dermochelys coriacea) is the largest of all living turtles. It is the only living species in the genus Dermochelys. As a sea turtle, the leatherback is the largest and heaviest. It can easily be differentiated from other modern sea turtles by its lack of a bony shell. Instead, the carapace of the leatherback turtle is covered by skin and the turtle's oily flesh. D. coriacea is the only extant member of the Family Dermochelyidae.

Anatomy and morphology

Leatherback turtles follow the general sea turtle body plan of having a large, dorsoventrally flattened, round body with two pairs of appendages, a very large head and a short tail. Like other sea turtles, the leatherback's flattened forelimbs are specially adapted for swimming in the open ocean. Claws are noticeably absent from both pair of flippers. The leatherback's flippers are the largest in proportion to its body among the extant sea turtles. Leatherback front flippers can grow up to 270 centimeters in large specimens. As the last surviving member of its family, the leatherback turtle has several distinguishing characteristics that differentiate it from other sea turtles. Its most notable feature is that it lacks the bony carapace of the other extant sea turtles. Instead of scutes, the leatherback's carapace is covered by its thick, leathery skin with embedded minuscule bony plates. Seven distinct ridges arise from the carapace, running from the anterior-to-posterior margin of the turtle's back. The entire turtle's dorsal surface is colored dark grey to black with a sporadic scattering of white blotches and spots. In a show of countershading, the turtle's underside is lightly colored.

Dermochelys coriacea adults average at around one to two meters long and weigh from around 250 to 700 kilograms.

Leatherbacks are also the reptile world's deepest-divers. Individuals have been discovered to be capable of descending to depths deeper than 1,200 meters.

Distribution

The leatherback turtle is a species with a cosmopolitan global range. Of all the extant sea turtle species, D. coriacea has the widest distribution, reaching as far north as Alaska and Norway and as far south as the Cape of Good Hope in Africa and the southernmost tip of New Zealand. Globally, there are three major, genetically-distinct populations. The Atlantic Dermochelys population is separate from the ones in the Eastern and Western Pacific, which are also distinct from each other. A third possible Pacific subpopulation has been proposed, specifically the leatherback turtles nesting in Malaysia. This subpopulation however, has almost been eradicated. While specific nesting beaches have been identified in the region, leatherback populations in the Indian Ocean remain generally unassessed and unevaluated.

Atlantic subpopulation

The leatherback turtle population in the Atlantic Ocean ranges almost all over the entire region. Their regional range spreads as far north as the North Sea and south to the Cape of Good Hope. Unlike other sea turtles, leatherbacks' feeding areas are colder waters where there is an abundance of their jellyfish prey which accounts for their more widespread range. However, only a few select beaches on both sides of the Atlantic are utilized by the turtles as nesting sites.

Off the Atlantic coast of Canada, leatherback turtles can be found feeding as far north as Newfoundland and Labrador. They have been sighted as far north as the Gulf of St. Lawrence near Quebec. Off the northeastern coast of the South American continent, a few select beaches between French Guiana and Suriname are primary nesting sites of several species of sea turtles, the majority being leatherbacks. A few hundred nest annually on the eastern coast of Florida. In Costa Rica, the beaches of Parismina are known nesting grounds of leatherback turtles. Further north, off the Pacific coast of Canada, leatherbacks have been seen on the beaches of British Columbia. The turtles prefer deep water but are most often seen within sight of land. Feeding grounds have been determined to be closer to land, in waters barely offshore. Unusually for a reptile, leatherbacks can survive and actively swim in colder waters; individual turtles have been found in waters that are at 4.5° Celsius.

Trophic ecology

Adult Dermochelys coriacea subsist on a diet almost entirely composed of jellyfish.

Life history

Like all sea turtles, leatherback turtles start their lives as hatchlings bursting out from the sands of their nesting beaches. Right after they hatch, the baby turtles are already in danger of predation. Many are eaten by birds, crustaceans or other reptiles before they reach the water. Once they reach the ocean they are generally not seen again until maturity. Very few turtles survive this mysterious period to become adults. It is known that juvenile Dermochelys spend a majority of their particular life stage in more tropical waters than the adults.

While the other species of sea turtles almost-always return to the same beaches they hatched from, female leatherback turtles have been found to be capable of switching to another beach within the same general region of their "home" beach. Chosen nesting beaches are made of soft sand since their shells and plastrons are softer and easily damaged by hard rocks. Nesting beaches also have shallower approach angles from the sea. This is a source of vulnerability for the turtles because such beaches are easily eroded. Females excavate a nest above the high-tide line with their flippers. One female may lay as many as nine clutches in one breeding season. About nine days pass between nesting events. The average clutch size of this particular species is around 110 eggs per nest, 85% of which are viable.

Cleavage of the cell begins within hours of fertilization, but development is suspended during the gastrulation period of movements and infoldings of embryonic cells, while the eggs are being laid. Development soon resumes, but the embryos remain extremely susceptible to movement-induced mortality in their nests until the membranes fully develop through the first 20 to 25 days of incubation, when the structural differentiation of body and organs (organogenesis) soon follows. The eggs hatch in about sixty to seventy days. As with other reptiles, the ambient temperature of the nest determines the sex of the hatchlings. After nightfall, the hatchlings dig their way to the surface and make their way to the sea.

As a global species with a range spanning both hemispheres, leatherback nesting seasons vary from place-to-place. Nesting occurs in February to July in Parismina, Costa Rica.

Etymology and Taxonomic history

Dermochelys coriacea is the only species in its genus Dermochelys. The genus in turn, contains the only extant members of the leatherback turtle family Dermochelyidae.

The species was first described in 1761 by Domenico Vandelli as Testudo coriacea. In 1816, the genus Dermochelys was coined by the French zoologist Henri Blainville. The leatherback was then reclassified under this own genus as Dermochelys coriacea. Later on, the species was classified in its own family of Dermochelyidae in 1843 by the zoologist Leopold Fitzinger. In 1884, the American naturalist Samuel Garman described members of the species as Sphargis coriacea schlegelii. The two described leatherback species were then united in D. coriacea with each given subspecies status as D. coriacea coriacea and D. coriacea schlegelii. The two subspecies were later rendered invalid synonyms of the species Dermochelys coriacea.

The turtle's common name comes from the leathery texture and appearance of its carapace. Aside from "leatherback" turtle, it has been called the "leathery turtle" in the past. In the Caribbean, some cultures consider the eggs of sea turtles to be aphrodesiacs.

Aside from targeted efforts at catching adults and collecting their eggs, there are many human activities that indirectly harm Dermochelys populations worldwide. As a pelagic species, D. coriacea individuals are occasionally caught as by-catch by commercial fishing vessels. As they are the largest sea turtles alive today, turtle excluder devices can be ineffective with adult leatherbacks of a particular size range. It is reported that an average of 1,500 mature females were accidentally caught annually in the 1990s.

The Leatherback Trust is an organization that was founded specifically towards the aim of the conservation of all marine turtles, specifically their namesake. The foundation was responsible for the establishment of a sanctuary in Costa Rica, the Parque Marino Las Baulas.

Country-specific conservation initiatives

As a species with a range encompassing dozens of coastal countries around the world, the leatherback turtle has been subject to differing country-specific laws regarding its conservation.

The United States has listed the leatherback turtle as an endangered species since June 2, 1970. The protected status of the species (in United States waters) was ratified with the passing of the U.S. Endangered Species Act three years after. Farther north in Canada, where the leatherback turtle can also be found, the Species Risk Act was established to make it illegal to exploit the species in Canadian waters. It has been classified endangered by the Committee on the Status of Endangered Wildlife in Canada. Ireland and Wales have initiated a joint leatherback conservation effort between the University of Wales Swansea and University College Cork. Funded by the European Regional Development Fund, the Irish Sea Leatherback Turtle Project as the project is called, focuses on serious research programs such as tagging and satellite tracking of individual leatherback turtles.

Several Caribbean countries have started conservation programs focused on using eco-tourism to bring attention to the plight of the leatherback. On the Atlantic coast of Costa Rica, the village of Parismina has one such initiative. Since 1998, the village has been assisting turtles with a hatchery program. Mayumba National Park in Gabon, Central Africa was created to protect the most important leatherback turtle nesting beach in Africa. More than 30,000 turtles come to nest on Mayumba's beaches between September and April each year. Leatherbacks used to nest in the thousands on many of Malaysia's beaches, including those at Terengganu where more than 3,000 nesting females were counted in the late 1960s. The last official count of nesting leatherback females on that beach was recorded to be a mere two females in 1993.

See also

• Chelonioidea. The sea turtle superfamily.
• Caretta caretta. The loggerhead turtle.
• Chelonia mydas. The green turtle.
• Eretmochelys imbricata. The hawksbill turtle.
• Lepidochelys kempii. The Kemp's Ridley turtle.
• Lepidochelys olivacea. The olive ridley turtle.
• Natator depressus. The flatback turtle.

References

Bibliography

• Database entry includes justification for why this species is critically endangered
• Wood R.C., Johnson-Gove J., Gaffney E.S. & Maley K.F. (1996) - Evolution and phylogeny of leatherback turtles (Dermochelyidae), with descriptions of new fossil taxa. Chel. Cons. Biol., 2(2): 266-286, Lunenburg.

External links

• Mayumba National Park Turtles Online Information about and photos of sea turtles and the world's most important leatherback nesting beach.
• ARKivePhotographs, Video
• The Oceanic Resource Foundation
• NOAA Office of Protected Resources
• Leatherback Sea Turtle at CRESLI
• The Great Turtle Race, a conservation group that monitors Leatherbacks as the swim from Costa Rica, where they've just laid their eggs, back to their natural territory of the Galapagos Islands.
• Tagging Of Pacific Predators, a contributor to The Great Turtle Race, this research group continues to tag and monitor Leatherbacks around the world, including the turtles from the race.
• Video of a leatherback turtle laying eggs Filmed in Tamarindo, Costa Rica
• Leatherback turtle research at Juno Beach, Florida