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Leatherback sea turtle

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Leatherback Sea Turtle
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Sauropsida
Order:
Testudines
Suborder:
Cryptodira
Family:
Dermochelyidae

Genus:
Dermochelys

Species:
D. coriacea
Binomial name
Dermochelys coriacea

The Leatherback Sea Turtle (Dermochelys coriacea) is the biggest of all living turtles, reaching a length of over 2.7 m (8.8 ft) and weight of 900 kg (2,000 lb), and is world's 4th largest reptile, behind the larger crocodiles. The Leatherback Sea Turtle is found in all tropical and subtropical oceans. It is the only extant species in the genus Dermochelys and the family Dermochelyidae. This species has many unique features that distinguish it greatly from other sea turtles. Its shell lacks the bony scutes of other turtles, comprising mainly connective tissue. Its metabolic rate is about 3 times higher than one would expect for a reptile of its size; this, coupled with counter-current heat exchangers, the insulation provided by its oily body and large size, allow it to maintain a body temperature as much as 18 °C (64 ºF) above that of the surrounding water. Some scientists hypothesize that the leatherback might have some capacity to generate its own body heat (like a mammal), although reptiles in general have been defined as ectotherms ('cold-blooded') and are thought not to be able to do so.

Physical characteristics

Leatherback Sea Turtle skeleton (Dinosaurland, Lyme Regis.)

The Leatherback is the largest of all living turtles. It is very different from other turtles in both appearance and physiology. It has a smooth, blackish carapace with ridges running from head to tail. This shell is not made of bone plates, or scutes, as in most sea turtles, but of soft connective tissue. The carapace does not meet the plastron at a sharp angle like in other turtles, but a gentle curve, giving the animal a semi-cylindrical appearance.

The front flippers of the Leatherback turtle are much larger than those of other turtles, both in proportion and in absolute size. Those of adults can span 8.85 ft (270 cm) from tip to tip.

The beak of the Leatherback turtle is specially hooked to help it bite jellyfish and its throat has backward-facing barbs to help it swallow them. These throat hooks have caused Leatherbacks problems - they swallow plastic bags, which look like the gelatinous animals they prey on, and these indigestible bags then clog up their throats, preventing them from feeding and eventually killing them. Dead leatherbacks have been found with plastic bags, pieces of hard plastic, and monofilament fishing line in their stomachs.

The world's biggest recorded Leatherback was washed ashore on Harlech beach, Gwynedd, in September 1988. It had drowned in fishing nets. It was one of the oldest recorded turtles, measuring almost nine feet (2.74 metres) in length and weighing 914 kg (2015 lb). Although popular media reported the turtle as 100 years old, aging techniques remain uncertain in leatherbacks, and their early growth rate is high, suggesting that even large adults may not be as ancient as other turtle species.

Diet

Leatherback turtles subsist on a diet of jellyfish, as well as other aquatic plants and animals. Giant leatherback turtles travel each year from the Caribbean to the UK and Europe, following the Gulf Stream in order to eat the jellyfish found there.

Breeding

Leatherbacks mate at sea; males never leave the water once they enter it as hatchlings. Females mate every three or four years, returning to the beaches where they themselves hatched, to deposit their eggs. One female may lay as many as ten clutches in one breeding season. The interval between laying is about nine days. Mating occurs after the age of ten years.

After encountering a female (who possibly exudes a pheromone to signal her reproductive status) the leatherback male uses head movements, nuzzling, biting or flipper movements to determine her receptiveness. Marine turtles often face a difficult and sometimes even dangerous task when attempting to reproduce. The male has to mount the female from behind and latch on in order to be able to copulate, but sometimes their shells obstruct this process. Mating can also become dangerous when the male is so desperately overeager to find a mate that he stays underwater for too long, and after encountering the female, he must spend another hour with no air. Fertilization is internal, and multiple males usually mate with a single female. This may have evolved to insure against male infertility, and sperm depletion, to allow females to select the highest quality sperm, and increase the genetic variation amongst offspring. However, studies have shown that the process of polyandry in sea turtles actually reduces fertilization success.

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 20-25 days of incubation, when the structural differentiation of body and organs (organogenesis) soon follows.

The nesting beach must be comprised of soft sand because their soft leatherback shells are easily damaged by hard rocks. The beach must also have a shallow approach angle 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. They then begin to lay their eggs, producing about 110 ova, 70 of which are large and fertile, the remaining 40 smaller and sterile. The female carefully back-fills the nest, making sure to disguise it from predators with a scattering of sand.

The female back-fills the nest
Problems playing this file? See media help.

The eggs hatch in about 60 days. Like some other reptiles, the ambient temperature of the nest determines the gender of the hatchlings. The eggs hatch while still buried under the sand. After nightfall, the hatchlings dig their way to the surface and make their way to the sea. Once they reach the ocean they are generally not seen again until maturity. Very few survive this mysterious period to become adults. Most are eaten by birds or other reptiles before they have a chance to reach the water. When the lights of a city are visible from a hatching site, Leatherback hatchlings are attracted to the lights and away from the sea. Many of these hatchlings are struck by traffic or otherwise perish.

Atlantic Leatherback Turtles nest between February and July from Georgia in the United States to the U.S. Virgin Islands in the Caribbean and to Suriname and the Guyanas. With nearly 30,000 turtles visiting its beaches each year from September to April, Mayumba National Park is the most important leatherback turtle nesting beach in Africa, and possibly worldwide. Pacific Leatherbacks nested on beaches from Malaysia to Costa Rica until the last few years, but since 2001 numbers have dropped dramatically, and Pacific Leatherbacks may be facing extinction.

Range and habitat

The leatherback turtle is found throughout the Atlantic, Pacific and Indian oceans, from as far north as Labrador, Alaska and Norway to as far south as Chile, the Cape of Bad Hope, Argentina, and the southern end of New Zealand. Mayumba, in Gabon, Central Africa, is home to the largest population of nesting leatherback turtles on the continent.

In the summer months, Atlantic Leatherback turtles are most common from the Gulf of Maine in the north to the coast of central Florida in the south. They have been sighted as far north as the Gulf of St. Lawrence in Canada. Pacific Leatherback turtles are most often seen off the Hawaiian Islands, where they are known to congregate north of the archipelago.

The turtles prefer deep water but are most often seen within sight of land. In the summer they are often seen basking near the surface, particularly in the Long Island Sound, where they have been injured by collisions with boat propellers.

Threats and conservation

In the United States the Leatherback turtle has been classified as endangered across its range since 1970. It is also endangered in Canada. It is also listed on Appendix 1 of the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES). This makes it illegal to harm or kill the turtles. Mayumba National Park in Gabon, Central Africa was created to protect the most important leatherback turtle nesting beach in Africa, and quite possibly the world. More than 30,000 turtles come to nest on Mayumba's beaches between September and April each year.

Adult Leatherback turtles are large animals that are not particularly vulnerable to natural predators. Eggs and hatchlings are most vulnerable to predation of all kinds. Birds, dogs and other opportunists are known to dig up nests and consume eggs. New hatchlings are also vulnerable on their journey from nest to sea. Once they enter the water they become prey to many new predators and very few survive to adulthood.

Human activity endangers Leatherback turtles in many ways. Though it is forbidden, eggs are harvested by people in Puerto Rico, the surrounding islands, and several African countries. Development of beaches can disturb or destroy the particular kind of habitat that Leatherbacks need to nest, and the lights of development can cause hatchlings to move away from the sea rather than toward it. Human use of beaches can crush nests and hatchlings or bury eggs too deep for the hatchlings to emerge. Finally humans may disturb nesting females out of curiosity.

While adults are at sea their major threats are all from humans. Ingesting plastic, rubber, tar, oil, and other synthetic materials can kill an adult Leatherback or severely injure it. Many have been injured by colliding with boats, especially in shallow water. The equipment associated with commercial fishing, including lines, nets, ropes, and cables can entangle adult turtles and cause them to drown. Though "Turtle Exclusion Devices" are mandated on nets, they often fail to allow an animal the size of an adult Leatherback to escape. The US NOAA estimates that about 640 adult Leatherback turtles are killed each year by commercial fishing enterprise.

Nets are purposely set for other kinds of sea turtles in some areas of Puerto Rico. Though they are not intended for Leatherbacks, some are occasionally caught. Despite its illegality, the practice continues.

Morphology of the leatherback turtle skeleton

File:CTdermochelys.jpg

View 3D computed tomographic (CT) animations of the skeleton of a hatchling leatherback turtle, and learn more about its distinctive carapace, at Digimorph.org .


Taxonomy and Extinct Species

  • Family Dermochelyidae
    • Genus Corsochelys
      • Corsochelys haliniches (extinct)
    • Genus Mesodermochelys
      • Mesodermochelys undulatus (extinct)
    • Genus Protosphargis
      • Protosphargis veronensis (extinct)
    • Genus Eosphargis
      • Eosphargis gigas (extinct)
      • Eosphargis breineri (extinct)
    • Genus Natemys
      • Natemys peruvianus (extinct)
    • Genus Egyptemys
      • Egyptemys eocaenus (extinct)
      • Egyptemys oregonensis (extinct)
    • Genus Cosmochelys
      • Cosmochelys dolloi (extinct)
    • Genus Psephophorus
      • Psephophorus calvertensis (extinct)
      • Psephophorus polygonus (extinct)
      • Psephophorus rupeliensis (extinct)
      • Psephophorus terrypratchetti (extinct)
    • Genus Dermochelys
      • Dermochelys coriacea (Modern Leatherback Sea Turtle)

References

  • Template:IUCN2006 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.
Wikimedia Commons has media related to Dermochelys coriacea.
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