An article by Mohan Pai
Illustration: Courtesy Canadian Museum of Nature
The longest-living marine species ever to ply world’s oceans, their survival into the next decade is doubtful.
They are the longest-living marine species to ever ply the world’s oceans. They survived catastrophic asteroid impacts and outlived the dinosaurs. But the leatherback sea turtle, the largest turtle in the world, is on the brink of extinction, and scientists question whether the animal will survive into the next decade. Over the last 22 years their numbers have declined in excess of 95 percent .
The leatherback turtle is the largest of all living sea turtles. and is the only living species in the genus Dermochelys. It can easily be differentiated from other modern sea turtles by its lack of a bony shell. Instead, its carapace is covered by skin and oily flesh. Instead of teeth the Leatherback turtle has points on its upper lip. It also has backwards spines in its throat to help it swallow food. Leatherback turtles can dive to depths as great as 4200 feet (1,280 meters).The leatherback turtle is entirely at home in the sea but comes to the shores to lay its eggs on sandy beaches. Cold blooded animals that they are, turtles live life in slow motion and live for hundred years or more. The leatherback turtle is a species with a cosmopolitan global range. In India leather backs come to the beaches of Kerala and Andaman and Nicobar islands where their eggs are a much prized food. This egg collection now threatens the existence of many sea turtle species. But notably enough, some fishing communities from Tamil Nadu have the tradition of not finishing off all the eggs in the clutch, but always leaving behind one, thus ensuring long time persistence of the race.
Leatherback turtles have a flattened, round body with two pairs of very large flippers 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 2.7 meters in large specimens, the largest flippers (even in comparison to its body) of any sea turtle. 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. The turtle’s underside is lightly colored.The adults average at around one to two meters long and weigh from around 250 to 700 kilograms. The largest ever found however was over three meters from head to tail and weighed 916 kilograms. That particular specimen was found on a beach on the west coast of Wales in the North Atlantic.Leatherbacks are also the reptile world’s deepest-divers. Individuals have been discovered to be able to descend deeper than 1,200 meters (3,937 feet).They are also the fastest reptiles on record. The 1992 edition of the Guinness Book of World Records has the leatherback turtle listed as having achieved the speed of 9.8 meters per second (35.28 kilometers per hour) in the water.
Of all the extant sea turtle species, the leatherback 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. The leatherback is found in all tropical and subtropical oceans, and its range has been known to extend well into the Arctic Circle. 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. The beach of Rantau Abang in Terengganu , Malaysia, had once had the largest nesting population in the world with 10,000 nests per year. However in 2008 only 2 leatherback turtles nested at Rantau Abang and unfortunately the eggs where infertile. The major cause for the decline in the leatherback turtles is the practice of egg collection in Malaysia. While specific nesting beaches have been identified in the region, leatherback populations in the Indian Ocean remain generally unassessed and unevaluated.
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, other reptiles and also people 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 leatherbacks spend a majority of their particular life stage in more tropical waters than the adults.
Adult leatherbacks are prone to long-distance bouts of migration. Migration in leatherback turtles occurs between the cold waters in which mature leatherbacks cruise in to feed on the abundant masses of jellyfish that occur in those waters, to the tropical and subtropical beaches in the regions where they were hatched from. In the Atlantic, individual females tagged in French Guiana off the coast of South America have been recaptured on the other side of the ocean in Morocco and Spain.Mating takes place at sea. Leatherback males never leave the water once they enter it unlike females which crawl onto land to nest. After encountering a female (who possibly exudes a pheromone to signal her reproductive status) a leatherback male uses head movements, nuzzling, biting or flipper movements to determine her receptiveness. Females are known to mate every two to three years. However, leatherbacks have been found to be capable of breeding and nesting annually. Fertilization is internal, and multiple males usually mate with a single female. However, studies have shown that this process of polyandry in sea turtles does not provide the offspring with any special advantages.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. The female carefully back-fills the nest after, disguising it from predators with a scattering of sand.
A leatherback turtle has set the record for ‘the longest trip for marine vertebrae between breeding and feeding sites’. It swam 20,558 kilometres, non-stop for 647 days!
Acknowledgements: Wikipedia, National Geographic, Canadian Museum of Nature
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