Definitions

denticulation

Green turtle

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

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

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

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 gasses 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.

Atlantic subpopulation

Chelonia mydas can generally be found throughout the entire Atlantic Ocean. Individuals have been spotted as far north as Canada in the Western Atlantic and the British Isles in the east. The subpopulation's southern range is known until past the southern tip of Africa in the east and Argentina in the Western Atlantic. The major nesting sites in the region can be found on various islands in the Caribbean, along the eastern shores of the continental United States, the eastern coast of the South American continent and most notably, on isolated islands in the north Atlantic. and asan d

In the Caribbean, major nesting sites have been identified on Aves Island, the U.S. Virgin Islands, Puerto Rico and Costa Rica. 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 Georgia, North and South Carolina and all along the east coast of Florida. Hutchinson Island in particular is a major nesting area in Florida waters. Notable nesting locations in South America include secluded beaches in Surinam and French Guiana. In the Southern Atlantic Ocean, the most notable nesting grounds for Chelonia mydas are found on the island of Ascension. 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 Florida include Indian River Lagoon, the Florida Keys, Florida Bay, Homosassa, Crystal River and Cedar Key.

Indo-Pacific subpopulation

In the Pacific, the range of the green turtle reaches as far north as the southern coast of Alaska and as far south as Chile in the east. The turtle's distribution in the Western Pacific is known as far north as Japan and even southern parts of Russia's Pacific coast and as far south as the northern tip of New Zealand and a few islands further south of Tasmania. The turtles can be found throughout the entire range of the Indian Ocean.

Significant nesting grounds are scattered throughout the entire region. Pacific green turtle nesting grounds are found in Mexico, the Hawaiian Islands, the South Pacific, the northern coast of Australia and Southeast Asia. In the Indian Ocean, major nesting colonies have been recorded in India, Pakistan 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 Madagascar.

East Pacific green turtles nesting grounds are well-studied all along the Mexican coast. These turtles have been found to feed in seagrass pastures in the Gulf of California. Green turtles belonging to the distinct Hawaiian subpopulation are known to nest at the protected French Frigate Shoals some 800 kilometers to the west of the Hawaiian Islands. In the Philippines, green turtles are known to nest in the Turtle Islands along with closely-related hawksbill turtles. There are also a few nesting beaches in Indonesia, one of them in the Meru Betiri National Reserve in East Java. The green sea turtles on the Great Barrier Reef 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 cays 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 Island.

Major nesting sites of green turtle are common on either side of the Arabian Sea, both in Ash Sharqiyah, Oman, and along the coast of Karachi, Pakistan. Some specific beaches along the area, such as Hawke's Bay and Sandspit, are the common nesting grounds for the region's C. mydas and L. olivacea subpopulation. Sandy beaches along Sindh and Balochistan are also known green turtle nest sites. Some 25 kilometers off the Pakistani coast, Astola island 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 City, Philippines. 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 type 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 frequent deep, pelagic waters where they spend the first few years of their lives.

Trophic ecology

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 Hawaiian 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

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 Caribbean, mating season is from June to September. The French Guiana 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 Pakistan, Indian Ocean 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.

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 opean 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 Island in the South Atlantic. 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 Hawaii, the native Hawaiian 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 Hawaii. 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 Indonesia, sea turtle eggs are a popular delicacy in Java. However, the turtle's flesh is regarded as ḥarām or "unclean" under Islamic law (Islam is the primary religion in the region). In Bali, 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 archipelago. 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.

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 Indies 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 List of Threatened Animals, according to the 1990 and 1994 editions of the IUCN Red List.

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 Sabah, Borneo. 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 States, the U.S. Fish and Wildlife Services classified Chelonia mydas as a threatened species, rendering it a federal offense to capture or otherwise kill an individual turtle. In part due to this, the Hawaiian 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 Academy on the Big Island have tagged thousands of specimens since the early 1990s. In the United Kingdom the species is protected by a Biodiversity Action Plan, due to harvesting in excess from human overpopulation and marine pollution. The Pakistani-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 Rica have been the subject of egg-collection limits since the 1950s. Two decades after, the Tortuguero National Park formally established in 1976 ensuring the protection of that region's nesting grounds. On Ascension Island 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

Bibliography

External links

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