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"Chelonia" redirects here. It is also the name of the superorder uniting turtles, tortoises and terrapins (Testudines) with the "proto-turtle" Australochelys.


Chelonia mydas, known as the green turtle is a large sea turtle belonging to the family Cheloniidae. It is the only species in the genus Chelonia. The range of the sea turtle extends throughout tropical and subtropical seas around the world, with two distinct populations in the Atlanticmarker and Pacific Oceansmarker. Their common name derives from the green fat underneath their shell.

The green turtle is a kind of sea turtle, possessing a dorsoventrally-flattened body covered by a large, teardrop-shaped carapace and a pair of large, paddle-like flippers. It is lightly-colored all around, while its carapace's hues range from olive-brown to black in Eastern Pacific green turtles. Unlike other members of its family such as the hawksbill and loggerhead turtles, Chelonia mydas is mostly herbivorous. The adults are commonly found in shallow lagoons, feeding mostly on various species of seagrass.

Like other sea turtles, green turtles are known to migrate long distances between their feeding grounds and the beaches they hatched from. Many islands worldwide have been called Turtle Islands primarily for the large amounts of green turtles that nest on their beaches each year. Female turtles dredge themselves onto beaches and lay eggs in nests that they dig during the night. After a period of time, hatchlings emerge from the nests and head for the water. Those that survive grow to maturity and have an average lifespan of 80 years or longer in the wild.

As a species recognized as endangered by the IUCN and CITES, Chelonia mydas is protected from exploitation in most countries worldwide. It is illegal to collect, harm or kill individual turtles. In addition, many countries have implemented various laws and ordinances to protect individual turtles and turtle nesting areas within their jurisdiction. However, the turtles' populations are still in danger because of several human practices. In some countries, the turtles are still hunted for their flesh and their eggs are collected from nests and eaten as a delicacy. Pollution indirectly harms the turtle populations both on the population and the individual scale. Many turtles die as a result of being caught in fishermen's nets and drowning. Finally, habitat loss due to human development is a major reason for the loss of green turtle nesting beaches.

Anatomy and morphology

Immature Hawaiian C. mydas.
The appearance of the green turtle is that of a typical sea turtle. Chelonia mydas has a dorsoventrally-flattened body, a beaked head at the end of a short neck, and paddle-like arms well-adapted for swimming. Adult green turtles are known to grow to long. While individuals have been caught that reached weights of up to 315 kilograms (695 lb), the average weight of mature individuals is around . The largest Chelonia mydas ever recorded weighed 395 kilograms (871 pounds).

Anatomically, there are a few characteristics that distinguish the green turtle from the other members of its family. Unlike the closely-related hawksbill turtle, the green turtle's snout is very short and its beak is unhooked. The horny sheath of the turtle's upper jaw possesses a slightly-denticulated edge while its lower jaw has stronger, serrated, more defined denticulation. The dorsal surface of the turtle's head has a single pair of prefrontal scales. Its carapace is composed of five central scutes flanked by four pairs of lateral scutes. Underneath, the green turtle has four pairs of infra-marginal scutes covering the area between the turtle's plastron and its shell. Mature C. mydas front appendages have only a single claw (as opposed to the hawksbill's two), although a second claw is sometimes prominent in young specimens.

The carapace of the turtle is known to have various color patterns that change over time. Hatchlings of C. mydas, like those of other marine turtles, have mostly black carapaces and light-colored plastrons. Carapaces of juveniles are dark brown to olive, while those of mature adults are either entirely brown, spotted or marbled with variegated rays. Underneath, the turtle's plastron is hued yellow. C. mydas limbs are dark-colored and lined with yellow, and are usually marked with a large dark brown spot in the center of each appendage.

Sea turtles spend almost all their lives submerged but must breathe air for the oxygen needed to meet the demands of vigorous activity. With a single explosive exhalation and rapid inhalation, sea turtles can quickly replace the air in their lungs. The lungs are adapted to permit a rapid exchange of oxygen and to prevent gases from being trapped during deep dives. The blood of sea turtles can deliver oxygen efficiently to body tissues even at the pressures encountered during diving. During routine activity green and loggerhead turtles dive for about 4 to 5 minutes and surface to breathe for 1 to 3 seconds.

Turtles can rest or sleep underwater for several hours at a time but submergence time is much shorter while diving for food or to escape predators. Breath-holding ability is affected by activity and stress, which is why turtles drown in shrimp trawls and other fishing gear within a relatively short time.

Distribution

The range of Chelonia mydas extends throughout tropical and subtropical oceans worldwide. There are two major subpopulations of C. mydas, the Atlantic and the Eastern Pacific subpopulations. Each population is genetically-distinct, with has its own set of nesting and feeding grounds within the population's known range.

C. mydas distribution.
Red circles are known major nesting sites.
Yellow circles represent minor nesting locations.


Atlantic subpopulation

Chelonia mydas can generally be found throughout the entire Atlantic Oceanmarker. Individuals have been spotted as far north as Canadamarker in the Western Atlantic and the British Islesmarker in the east. The subpopulation's southern range is known until past the southern tip of Africa in the east and Argentinamarker in the Western Atlantic. The major nesting sites in the region can be found on various islands in the Caribbeanmarker, along the eastern shores of the continental United Statesmarker, the eastern coast of the South American continent and most notably, on isolated islands in the North Atlanticmarker.

In the Caribbean, major nesting sites have been identified on Aves Islandmarker, the U.S.marker Virgin Islandsmarker, Puerto Rico and Costa Ricamarker. One of the most important nesting grounds for the region's green turtle population can be located in Tortuguero in Costa Rica. In fact, a great majority of the Caribbean region's C. mydas population hails from a few beaches in Tortuguero. Within United States waters, minor nesting sites have been noted in the states of Georgiamarker, Northmarker and South Carolinamarker and all along the east coast of Floridamarker. Hutchinson Islandmarker in particular is a major nesting area in Florida waters. Notable nesting locations in South America include secluded beaches in Surinammarker and French Guianamarker. In the Southern Atlantic Ocean, the most notable nesting grounds for Chelonia mydas are found on the island of Ascensionmarker. On that particular island, annual nesting occurs in the volume of around 6,000 to 13,000 individual turtle nests.

In contrast with the sporadic distribution of their nesting sites, Chelonia mydas feeding grounds are much more widely distributed throughout the region. Important feeding grounds for the green sea turtle in Floridamarker include Indian River Lagoon, the Florida Keysmarker, Florida Baymarker, Homosassamarker, Crystal River and Cedar Keymarker.

Indo-Pacific subpopulation

In the Pacificmarker, the range of the green turtle reaches as far north as the southern coast of Alaskamarker and as far south as Chilemarker in the east. The turtle's distribution in the Western Pacific is known as far north as Japanmarker and even southern parts of Russiamarker's Pacific coast and as far south as the northern tip of New Zealandmarker and a few islands further south of Tasmaniamarker. The turtles can be found throughout the entire range of the Indian Oceanmarker.

Significant nesting grounds are scattered throughout the entire region. Pacific green turtle nesting grounds are found in Mexicomarker, the Hawaiian Islands including O'ahu's Turtle Bay, the South Pacific, the northern coast of Australia and Southeast Asia. In the Indian Ocean, major nesting colonies have been recorded in Indiamarker, Pakistanmarker and other coastal countries in the region. A few nesting grounds have been reported along the east coast of the African continent including some islands in the waters around Madagascarmarker.

East Pacific green turtles nesting grounds are well-studied all along the Mexicanmarker coast. These turtles have been found to feed in seagrass pastures in the Gulf of Californiamarker. Green turtles belonging to the distinct Hawaiian subpopulation are known to nest at the protected French Frigate Shoalsmarker some 800 kilometers to the west of the Hawaiian Islands. In the Philippinesmarker, green turtles are known to nest in the Turtle Islandsmarker along with closely-related hawksbill turtles. There are also a few nesting beaches in Indonesiamarker, one of them in the Meru Betiri National Reserve in East Java. The green sea turtles on the Great Barrier Reefmarker have two genetically distinct populations; one in the Northern Great Barrier Reef, and the other in the Southern half of the reef. Within the reef, twenty separate locations consisting of small islands and caysmarker were identified as nesting sites for either population of C. mydas. Of these, the most important green turtle nesting ground was identified to be on Raine Islandmarker.

Major nesting sites of green turtle are common on either side of the Arabian Seamarker, both in Ash Sharqiyahmarker, Omanmarker, and along the coast of Karachimarker, Pakistanmarker. Some specific beaches along the area, such as Hawke's Baymarker and Sandspit, are the common nesting grounds for the region's C. mydas and L. olivacea subpopulation. Sandy beaches along Sindhmarker and Balochistanmarker are also known green turtle nest sites. Some 25 kilometers off the Pakistani coast, Astola islandmarker is another known nesting beach.

On December 30, 2007, fishermen, using a "hulbot-hulbot" or a fishnet accidentally caught an 80-kilogram, 93 centimeters in length and 82 cm wide, green sea turtle off Barangay Bolong, Zamboanga Citymarker, Philippinesmarker. December is breeding season of the green sea turtles near the Bolong beach.

Ecology and life history

As one of the oldest sea turtle species studied, much of what is known of sea turtle ecology was gleaned from studies of green turtles. The ecology of Chelonia mydas changes drastically with each succeeding stage of its life history. For instance, newly-emerged hatchlings are carnivorous, pelagic organisms part of the open ocean mini-nekton. In contrast, immature juveniles and adult turtles are commonly found in seagrass meadows closer inshore as herbivorous grazers.

Habitat

Green turtles alternate between three habitat types depending on their current life history stage. Nesting beaches are where the turtles return to lay eggs. Mature turtles spend most of their time in coastal, shallow waters with lush seagrass beds. Seagrass meadows within inshore bays, lagoons and shoals are common locations where adult Chelonia mydas can often be found. This particular species is known to be very selective about their feeding and mating sites and entire generations will often alternately migrate between the same feeding and nesting areas.

After hatching, turtles in their first five years are known to spend a majority of their early life stages in convergence zones within the open ocean. These young turtles are rarely seen as they swim in deep, pelagic waters where they spend the first few years of their lives.

Trophic ecology

C. mydas swimming, Hawaii.
As large and well-protected animals, adult green turtles have few enemies and even fewer predators. Only human beings and the larger sharks are known to feed on C. mydas adults. Specifically, tiger sharks (Galeocerdo cuvier) are known predators of adult green turtles in Hawaiianmarker waters. Juvenile turtles and recently-emerged hatchlings have significantly more predators, including crabs, small mammals and shorebirds.

Adult Chelonia mydas are obligately herbivorous. They almost-exclusively feed on various species of seagrasses and seaweed. They have been observed grazing on various species of macroalgae, specifically Caulerpa, Turbinaria, Spyridia, Codium, and Ulva. While mature green turtles are entirely herbivorous, juveniles are known to subsist on a plethora of marine invertebrates. Select preferred prey items include smaller cnidarians and crustaceans. Their digestive intake of plant matter grows larger as they age, until as mature adults they become obligate herbivores. While it has been previously stated that green turtles do not feed while at their respective nesting areas, it has been shown that gravid turtles do in fact feed while in the waters surrounding their nesting grounds.

Life history

Female green turtle nesting on a beach.
Unlike most sea turtles, which spend most of their adult lives in the ocean, Pacific green turtles are known to willingly crawl onto secluded beaches during the day to bask in the sun.

Green turtles migrate long distances between their chosen feeding sites and the beaches from where they hatched. Some C. mydas are known to swim distances of greater than 2,600 kilometers (1,400 nmi) to reach their spawning grounds. Mature turtles will often return to the same exact beach from which they hatched. Individual female green turtles usually mate every two to four years. Males on the other hand, are known to make the trip to their breeding areas every year. As with many species that are found across a wide range of latitudes, mating seasons vary between populations. For most Chelonia mydas in the Caribbeanmarker, mating season is from June to September. The French Guianamarker nesting subpopulation nests from March to June. In the tropics, green turtles are known to nest throughout the year, with some subpopulations preferring particular times of the year. In Pakistanmarker, Indian Oceanmarker C. mydas nest all year-round but prefer to nest during the months of July to December.

Green turtles reproduce in the typical way that marine turtles do so. Female turtles control mating; males cannot force females to mate. While it does not seem to offer increased survival among the hatchlings, a few green turtle populations are known to undergo polyandry when mating. After mating in the water, the females haul themselves onto the beach above the high tide line. Upon reaching a suitable nesting site, the gravid female then digs a hole with her hind flippers and deposits a number of eggs in the nest. The number of eggs laid per litter depends on the age of the female and differs from species to species, but C. mydas clutches range between 100 to 200 eggs. After laying eggs, the female then covers the nest with sand and returns to the sea.

C. mydas hatchling.
After around 45 to 75 days, the eggs hatch. As with other marine turtles, C. mydas eggs hatch during the night and the newly-emerged turtles instinctively head directly towards the water's edge. This undoubtedly is the most dangerous time in a turtle's life, as the hatchlings make their way to the water, various predators such as gulls and crabs pick off many turtles. A significant percentage of turtle hatchlings never make it to the ocean. Just like other sea turtles, little is known of the early life history of newly-hatched green turtles. After this trek to the ocean juvenile green turtles spend from three to five years in the open ocean as carnivores before they settle as immature juveniles into a more herbivorous, shallow-water lifestyle. It is speculated that they take twenty to fifty years to reach mature size. Individuals of the species are known to live up to eighty years in the wild.

One of the most significant mass-nesting sites for this species is located on Ascension Islandmarker in the South Atlanticmarker. Each year on the island, thousands of C. mydas create between 6,000 and 15,000 nests. These particular turtles are among the largest green turtles in the world, many more than a meter in length and weighing up to 300 kilograms.

Evolutionary history

The green turtle is a member of the tribe Chelonini. In a study conducted in 1993, the status of the genus Chelonia with respect to the other marine turtles was clarified. The carnivorous Eretmochelys (hawksbill), Caretta (loggerhead) and Lepidochelys (Ridley) were confirmed in the tribe Carettini. Herbivorous Chelonia were found distinct enough to warrant their status while establishing that Natator (flatback) was further-removed than previously believed.

Etymology and taxonomic history

The species was originally described by Linnaeus in 1758 as Testudo mydas. In 1868, Bocourt described a particular species of sea turtle as Chelonia agassizii (Chelonia agassizi is a commonly-cited misspelling of this taxon). This "species" was referred to as the black sea turtle. However, research determined that the "black sea turtle" was not genetically distinct from C. mydas and thus taxonomically not a separate species. These two separate species were then united in the same species, Chelonia mydas and were given subspecies status. C. mydas mydas referred to the originally described population while C. mydas agassizi referred to the Pacific population. This subdivision was later determined to be invalid and all members of the species were then designated Chelonia mydas. The oft-mentioned name C. agassizi remains an invalid junior synonym of C. mydas.

The species' common name is derived not from any particular green external coloration of the turtle. The green turtle is so-called because of the greenish color of the turtle's fat, which is only found in a layer between their inner organs and their shell. As a species found worldwide, the green turtle is called differently in some languages and dialects. In Hawaiimarker, the Hawaiian language word honu is used to refer to this species.

Importance to humans

While in most countries it is now illegal to hunt Chelonia mydas along with the other members of its family, sea turtles continue to be caught worldwide. Along with other sea turtles, Chelonia mydas are caught both intentionally and unintentionally in select regions of the world. Prior to the implementation of various protection measures, the turtles' skin was tanned and used as leather for handbags, especially in Hawaiimarker. In ancient China, the flesh of sea turtles including and especially C. mydas was considered a culinary delicacy. Particularly for this species, the turtle's calipee, fat and cartilage are sought as ingredients for making turtle soup.

In some countries like India and China it is considered as a sacred animal according to vastu, astrology and feng shui. Putting turtles into aquariums or in one's house is considered to ensure the family's life to be long and it eliminates all negative energies of the house.

In Indonesiamarker, sea turtle eggs are a popular delicacy in Javamarker. However, the turtle's flesh is regarded as ḥarām or "unclean" under Islamic law (Islam is the primary religion in the region). In Balimarker, the demand for turtle meat to satisfy traditional consumption at ceremonial and religious feasts has encouraged the harvesting of turtles in the furthest and remotest parts of the Indonesian archipelagomarker. Bali has been importing sea turtles since the 1950s as its own turtle supplies were said to be severely depleted. The ethnic Balinese do not eat the eggs, which are instead sold to local Muslims. The former traditional uses of turtle on Bali were once deemed sustainable, but have been questioned considering a vastly larger human population and thus greater demand. The harvest was until recently described to be the most intensive in the world. Indonesia's government restricted turtle trade and consumption in 1999 over concerns with the turtles' decreasing population and threat of a tourist boycott to the island. It also rejected a request made by Bali Governor I Made Mangku Pastika in November 2009 to set a quota of 1,000 turtles to be killed in Hindu religious ceremonies. While conservationists respect the need for turtles in rituals, they disagreed with the proposed quota number.

Before the inclusion of the turtles in the Endangered Species Act and the Convention on International Trade in Endangered Species, commercial farms such as the Cayman Turtle Farm in the West Indiesmarker bred the turtles for commercial sale. The farms held as many as 100,000 turtles at any one time. When the markets were closed due to protection measures, some farms went bankrupt and most drastically reduced their stock. The farms have since been converted into tourist attractions with around 11,000 turtles at any one time.

Conservation

There are various threats to the species' survival. Direct and directed threats to individual turtles include hunting of turtles for their flesh and shells and the harvesting of their eggs. More prevalent indirect threats include casualties due to turtles being injured by boat propellers, being caught as bycatch by fishermen's nets without TED, pollution and habitat destruction. Pollution effects would include direct-impact disturbances such as effluent from harbors near nesting sites. Habitat loss usually occurs due to human development of their nesting areas. Urban development of beaches, reclamation and an increased level of tourism are examples of such development. An infectious tumor-causing disease known as fibropapillomatosis is also a problem in some green turtle populations. The disease kills a sizeable fraction of the turtles that it infects, though some turtles seem to be resistant to the disease.

Because of these, the many populations of Chelonia mydas worldwide are in various states of vulnerability. The Mediterraneanmarker green turtle population is particularly listed as critically endangered. In the East Pacificmarker, green turtle subpopulations in Hawaiimarker and Southern California have been designated threatened. Specific Mexicanmarker subpopulations are listed as endangered. In the Caribbeanmarker, the Floridamarker nesting population is also listed as endangered. In the Indian Oceanmarker, the World Wide Fund for Nature has labeled nesting populations in Pakistanmarker as "rare and declining."

Global conservation initiatives

Since 2004, Chelonia mydas has been classified by the IUCN Red List of Threatened Species as endangered. It is listed as classified under the EN A2bd criteria, which essentially states that the species' wild populations are facing a high risk of extinction because of several factors. These factors include a probably reduction of more than 50% in the size of the worldwide C. mydas population over the past decade. This was determined by using abundance indices and by projecting a potential level of exploitation of the species' numbers.

The species has been officially classified as an endangered species since 1982, when the International Union for the Conservation of Nature listed Chelonia mydas as endangered. Throughout various reassessments and subsequent publications, the conservation status of the turtle has not changed over time. The 1986, 1988, 1990 and 1994 editions of the IUCN Red List retained the species' endangered status. In the landmark 1996 edition of the Red List, C. mydas remained listed as an endangered species. In 2001, a petition was filed to delist the species as an endangered species. At the time, the species was listed as endangered under the strict EN A1abd criteria. The petitioner claimed that at the time, there was ample evidence to suggest that some green turtle populations were large, stable and in some cases, increasing. The IUCN Standards and Petitions Subcommittee determined in a ruling that visual counts of nesting females could not be considered as "direct observation" and thus downgraded the species' status as EN A1bd - retaining the turtle's endangered status.

As a member of the family Cheloniidae, Chelonia mydas is listed on Appendix I of the Convention on International Trade in Endangered Species as of May 3, 2007. The species was originally listed on Appendix II in 1975. The entire family was put onto Appendix I in 1977, with the exception of the Australian population of C. mydas. In 1981, all populations of the species were brought into Appendix I, including the Australian population. As covered by Appendix I of CITES, it is illegal to import or export, kill, capture or harass green turtles.

Country-specific conservation initiatives

In addition to management by global entities such as the IUCN and CITES, specific countries around the world whose jurisdiction turtle nesting and feeding grounds fall under have taken specific conservation efforts in order to protect the species.

Eco-tourism has been one specific thrust in Sabahmarker, Malaysiamarker. The island of Pulau Selingan is home to a turtle hatchery. Staff on the island collect some of the eggs laid each night and place them in a hatchery to protect them from predators. Incubation of the eggs apparently takes around sixty days. Once hatched, tourists are permitted to assist in the release of the baby turtles into the sea. In the United Statesmarker, the U.S. Fish and Wildlife Services and National Marine Fisheries Service classified Chelonia mydas as a threatened species under the Endangered Species Act, rendering it a federal offense to capture or otherwise kill an individual turtle. In part due to this, the Hawaiianmarker green turtle subpopulation has made a remarkable comeback and is now also the subject of eco-tourism and has become something of a state mascot. Students of Hawaii Preparatory Academymarker on the Big Island have tagged thousands of specimens since the early 1990s. In the United Kingdommarker the species is protected by a Biodiversity Action Plan, due to harvesting in excess from human overpopulation and marine pollution. The Pakistanimarker-branch of the World Wide Fund for Nature has been initiating various projects for secure turtle hatching since the 1980s. However, the population has continued to decline due to various factors.

In the Atlantic, conservation initiatives have centered around nesting sites in the Caribbean. The Tortuguero nesting beaches in Costa Ricamarker have been the subject of egg-collection limits since the 1950s. Two decades after, the Tortuguero National Parkmarker formally established in 1976 ensuring the protection of that region's nesting grounds. On Ascension Islandmarker where some of the species' most important nesting beaches are, an active conservation program has been implemented.. Karumbé has been monitoring foraging and developmental areas of juvenile green turtles Chelonia mydas in Uruguay from 1999.

See also



References

  1. Campaign to Protect Turtle Bay (HI)
  2. Abs-Cbn Interactive, Green sea turtle caught in Zamboanga
  3. Sumertha, I.N. 1974. Perikanan penyu dan cara pengelolaan di Indonesia. Dokumen. Kom. IPB 8: 1-18. Cited in


Bibliography



External links



Gallery

Image:Chelonia mydas got to the surface to breath.jpg|Chelonia mydas breaking the surface to breathe.Image:GreenSeaTurtle-HolChanMarineReserve-Belize.JPG|Chelonia mydas photographed at Hol Chan Marine Reserve off Ambergris Cayemarker, Belizemarker.Image:Courtship of green turtles.jpg|Chelonia mydas Courtship.


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