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Leatherback Sea Turtle
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The leatherback turtle (Dermochelys coriacea) is the largest of all living sea turtles and the fourth largest reptile behind three crocodilians. It 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. Dermochelys coriacea is the only extant member of the family Dermochelyidae.
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The leatherback turtle (Dermochelys coriacea) is the largest of all living sea turtles and the fourth largest reptile behind three crocodilians. It 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. Dermochelys coriacea is the only extant member of the family Dermochelyidae. Instead of teeth the Leatherback turtle has points on the tomium of 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).
Anatomy and morphology
Leatherback turtles follow the general sea turtle body plan of having a large, dorsoventrally 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. 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. 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.
Physiology
The metabolic rate of the leatherback is about four 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 flesh and large body size, allow it to maintain a body temperature as much as 18°C (64°F) above that of the surrounding water. Its large size also gives the leatherback more capacity to maintain its body temperature than smaller, more ectothermic reptiles.
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.
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. 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.
Recent estimates of global nesting populations indicate 26,000 to 43,000 nesting females annually, which is a dramatic decline from the 115,000 estimated in 1980. These declining numbers have contributed to conservation efforts to stabilize the leatherback sea turtles and move their species away from the current status of critically endangered
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. The most significant nesting sites in the Atlantic are in Suriname and French Guiana in the Caribbean and Gabon in Central Africa. The beaches of Mayumba National Park in Mayumba, Gabon are home to the largest nesting population of leatherback turtles on the African continent. 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.
Pacific subpopulation
Leatherback turtles in the Pacific Ocean have been determined to belong to two distinct populations. One population is known to nest on beaches in Papua, Indonesia and the Solomon Islands while their foraging grounds are across the Pacific in the northern hemisphere along the coast of Oregon in North America. The Eastern Pacific population forages in the southern hemisphere, in waters along the western coast of the South American continent while they nest in beaches on the Pacific side of Central America, specific nesting grounds being in Mexico and Costa Rica. The Malaysian nesting population, reduced to less than a hundred individuals as of 2006, has been proposed as a third major Pacific subpopulation.
There are two major leatherback feeding areas in the continental United States. One well-studied area is just off the northwestern coast of the United States near the mouth of the Columbia River. These waters are excellent feeding grounds for the turtles, where they are believed to be foraging in the nutrient-rich waters of the North Pacific. The other American foraging area for the turtles is located in the state of California. Further north, off the Pacific coast of Canada, leatherbacks have been seen on the beaches of British Columbia.
Indian Ocean subpopulation
While there are few researches that have been done on Dermochelys populations in the Indian Ocean, nesting populations are known from Sri Lanka and the Nicobar Islands. It is proposed that these turtles form a separate, genetically distinct Indian Ocean subpopulation.
Ecology and life history
Habitat
Leatherback turtles can be found primarily in the open ocean. Scientists tracked a leatherback turtle that swam from Indonesia to the U.S. in an epic 20,000-kilometer (13,000-mile) journey over a period of 647 days as it searched for food. 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 as cold as 4.5° Celsius.
The favoured breeding beaches of the leatherback turtle are mainland sites facing deep water and they seem to avoid those sites protected by coral reefs.
Trophic ecology
Adult Dermochelys coriacea subsist on a diet almost entirely composed of jellyfish. Due to its obligate feeding nature, it has been hypothesized that leatherback turtles play a role in the control of jellyfish populations. Leatherbacks are also known to feed on other soft-bodied marine organisms such as tunicates and cephalopods.
Dead leatherbacks that wash ashore have been studied to be veritable microecosystems on their own while in the process of decomposition. A drowned leatherback carcass observed in 1996 was observed to have been host to sarcophagid and calliphorid flies after being picked open by a pair of Coragyps atratus vultures. Infestation by known carrion-eating beetles of the Scarabaeidae, Carabidae and Tenebrionidae families soon followed suit. After days of decomposition, beetles from the families Histeridae and Staphylinidae and anthomyiid flies invaded the corpse as well. All in all, organisms from more than a dozen families took part in decomposition of the leatherback carcass.
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, 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 Dermochelys spend a majority of their particular life stage in more tropical waters than the adults.
Adult Dermochelys 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.
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. Farther east in French Guiana, Dermochelys populations nest from March to August. Atlantic leatherback turtles nest between February and July from South Carolina in the United States to the U.S. Virgin Islands in the Caribbean and to Suriname and Guyana. With nearly 30,000 turtles visiting its beaches each year to April, Mayumba National Park is the most important leatherback turtle nesting beach in Africa, and possibly worldwide.
Evolutionary history
Leatherback turtles have been around in some form since the first true sea turtles evolved over 110 million years ago during the Cretaceous. The dermochelyids, as represented by the single living species D. coriacea, are close relatives of the family Cheloniidae which contain the other species of extant sea turtles. However, phylogenetic analysis has determined their sister taxon to be the extinct family Protostegidae which also included species with no hard carapace.
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. The turtle was also once referred to as the "trunk" turtle, though the name is now in disuse.
Importance to humans
The harvesting of sea turtle eggs is still practiced by people around the world. Asian exploitation of the turtle's nests have been cited as the most significant factor for the species' global population decline. In Southeast Asia, the collection of leatherback eggs has led to a near-total collapse of local nesting populations in specific countries like Thailand and Malaysia. Specifically in Malaysia, where the turtle is practically locally extinct, the eggs are considered a delicacy. In the Caribbean, some cultures consider the eggs of sea turtles to be aphrodisiacs.
Conservation
Adult leatherback turtles are large animals that have few natural predators. The most vulnerable stages in a leatherback's life are their early life stages at which point they are most vulnerable to predation of all kinds. Birds, small mammals and other opportunists are known to dig up nests and consume eggs. New hatchlings are also vulnerable on their journey from nest to sea. Shorebirds and crustaceans are known to prey on the turtles scrambling for the sea. Once they enter the water they become prey to a whole new host of predators such as predatory fishes and cephalopods. Very few survive to adulthood.
Leatherback turtles have slightly fewer human-related threats than the other sea turtle species. As their flesh contains higher oil and fat content than other species', there is not much demand for their flesh. However, human activity still significantly endangers leatherback turtles in direct and indirect ways. Directly, a small amount of leatherback turtles are caught for their meat by subsistence fisheries. Nests are raided for eggs by humans in a few places around the world, such as Southeast Asia.
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. Pollution, both chemical and physical, can also be fatal to leatherback turtles. With their main diet consisting of jellyfish, many turtles die from malabsorption and intestinal blockage following the ingestion of balloons and plastic bags which resemble their prey. Chemical pollution has also had an adverse effect of the Dermochelys population. A high level of phthalates has been measured in the yolk of D. coriacea eggs.
Global conservation initiatives
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.
Conservation of the Pacific and Eastern Atlantic leatherback populations was included among the top ten issues in turtle conservation in the first State of the World's Sea Turtles report published in 2006. Specifically noted were the significant population declines in the Mexican, Costa Rican and Malaysian populations. The Eastern Atlantic nesting population was noted for being threatened by increased fishing pressures from Eastern South American countries in whose waters the leatherbacks forage.
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.
A more drastic measure that is being studied by the Malaysian Fisheries Department is cloning. In mid-2007, the Fisheries Department expressed a plan to clone leatherback turtles to replenish the country's rapidly-declining Dermochelys population. Some conservation biologists however, are skeptical of the proposed plan as cloning has been done only on mammals such as dogs, sheep, cats and cows, and uncertainties persist about cloned animals' health and life spans. 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.
In Brazil, reproduction of the leatherback turtle is being assisted by the IBAMA's "projeto TAMAR" (TAMAR project), which aims to protect all sea turtles in the Brazilian coast, by assisting their nests and preventing accidental kills by fishing boats. The last official count of nesting leatherback females in Brazil was recorded to be only seven females.
It is listed as Vulnerable under Australia's Environment Protection and Biodiversity Conservation Act 1999, and as Endangered under Queensland's Nature Conservation Act 1992.
See also
Bibliography
External links
- Information about and photos of sea turtles and the world's most important leatherback nesting beach.
- Photographs, Video
- , 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.
- , 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.
- Filmed in Tamarindo, Costa Rica
- Leatherback Turtle in Irish waters.
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