Green sea turtle

Atlantic subpopulation

The green sea turtle can generally be found throughout the Atlantic Ocean. Although the species is most abundant in tropical climates, green sea turtles can also be found in temperate climates, and individuals have been spotted as far north as Canada in the western Atlantic, and the Cimbrian peninsular 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 can be found on various islands in the Caribbean, along the Atlantic coast of Florida in the United States, the eastern coast of the South American continent and most notably, on isolated North Atlantic islands.

In the Caribbean, major nesting sites have been identified on Aves Island, the U.S. Virgin Islands, Puerto Rico, the Dominican Republic, and Costa Rica. In recent years, there are signs of increased nesting in the Cayman Islands.^[35] One of the region's most important nesting grounds is in Tortuguero in Costa Rica.^[36] In fact, the majority of the Caribbean region's C. mydas population hails from a few beaches in Tortuguero.^[37] Within United States waters, minor nesting sites have been noted in the states of Georgia, North Carolina, and South Carolina. Florida's east coast is the largest nesting site in the United States. Hutchinson Island in particular is a major nesting area in Florida waters. Florida has several annual nesting periods when local beaches are closed or cordoned off to protect nesting sites. According to Green Sea Turtle Watch, in 2015 more than 37,000 green sea turtle nests were documented in Florida, a record number. In addition to sporadic distribution of nesting sites, feeding grounds are much more widely distributed throughout Florida. Important feeding grounds in Florida include Indian River Lagoon, the Florida Keys, Florida Bay, Homosassa, Crystal River, and Cedar Key.^[25][38]

Notable locations in South America include secluded beaches in Suriname and French Guiana.^[39] In the Southern Atlantic Ocean, the most notable nesting grounds for Chelonia mydas are found on the island of Ascension,^[25] hosts 6,000–13,000 turtle nests.^[40][41][42]

Indo-Pacific subpopulation

In the Pacific, its range 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 reaches north to Japan and southern parts of Russia's Pacific coast, and as far south as the northern tip of New Zealand and a few islands south of Tasmania. Significant nesting grounds are scattered throughout the entire Pacific region, including Mexico, the Hawaiian Islands, the South Pacific, the northern coast of Australia, and Southeast Asia. Major Indian Ocean nesting colonies include India, Pakistan, Sri Lanka and other coastal countries.^[43]

The turtles can also be found throughout the Indian Ocean; the east coast of the African continent hosts a few nesting grounds, including islands in the waters around Madagascar.^[43]

Galápagos green turtle

The population that has often been known as the Galápagos green turtle have been recorded and observed in the Galápagos as far back as the 17th century by William Dampier.^[56] Not much attention has been paid to them due to the overwhelming research done on the Galápagos giant tortoises.^[57] Only over the last 30 years have extensive studies been performed covering the behaviors of the Galápagos green turtles. Much of the debate that has surrounded them recently is over the binomial classification of the species.^[58] At one point the name Chelonia agassizii was applied to this population as a separate species.^[18] Analysis of mitochondrial and nuclear DNA of 15 nesting beaches,^[58] however, has demonstrated that there is not only no significant distinction of this population but that it would be paraphyletic to recognise it. As such the species name Chelonia agassizzii is considered a junior synonym of Chelonia mydas ^[58] as such it is considered as a local variant of the populations of the East Pacific waters and those of other nesting areas.^[58]

The morphological distinctiveness of the Galápagos green turtle has given rise to the debate,^[18] but evidence of taxonomic distinctiveness is best served using the combination of multiple datasets. The two most notable morphological distinctions are the considerably smaller adult size and the much darker pigmentation of the carapace, plastron, and extremities.^[18] Other distinctions are the curving of the carapace above each hind flipper, the more dome-shaped carapace, and the very long tail of adult males.^[59] Three possibilities have arisen from their unique characteristics: agassizii is a separate species from C. mydas, it is a subspecies of green sea turtle, or it is simply a color mutation.^[59] These facts have led to the debate over binomial separation however due to the significance of the DNA testing results there have been no distinctions made at this time.^[58] At a meeting for sea turtle scientists and their collaborators in 2000, the evidence for the taxonomic position of the Galápagos green turtle was reviewed and a majority among the participants supported treating it as a population or subspecies of the green turtle (instead of a separate species).^[60] However, this is possibly a case of political taxonomy. As such the three major international checklists that cover turtles of the world Reptile Database^[61] the checklist of Fritz and Havas (2007)^[3] and the IUCN Checklist (TTWG 2017)^[62] all consider this a junior synonym.

Diet

The diet of green turtles changes with age.^[68] Juveniles are carnivorous, but as they mature they become omnivorous.^[69] Young sea turtles eat fish and their eggs, sea hare eggs, hydrozoans, bryozoans, molluscs, jellyfish, small invertebrates, echinoderms, tunicates, insects, worms, sponges, algae, sea grasses, leaves, tree bark, and crustaceans.^{[70][71][34][72]} Green sea turtles have a relatively slow growth rate because of the low nutritional value of their diet. Body fat turns green because of the consumed vegetation.^[69] This diet shift has an effect on the green turtle's skull morphology.^[73] Their serrated jaw helps them chew green and red algae (such as filamentous red alga (Bostrychia), red moss (Caloglossa), freshwater red algae (Compsopogon), lobster horns (Polysiphonia), sea lettuce (Ulva lactuca), green seaweed (Gayralia), and crinkle grass (Rhizoclonium)) and sea grasses.^[71][74] They also consume large quantities of wetland plants such as Avicennia schaueriana and Sporobolus alterniflorus, which are commonly found in salt marshes.^[71] Most adult sea turtles are strictly herbivorous.^[69]

Predators and parasites

Only some human beings and the larger sharks feed on C. mydas adults. Specifically, tiger sharks (Galeocerdo cuvier) hunt adults in Hawaiian waters.^[75] The tiger shark is the main predator of the green turtle as it will prey on green turtles of all sizes. The tiger shark has often been seen feeding on green turtles near their nesting beaches because they are restricted in the area of their nesting beaches and vulnerable to predation.^[76] Juveniles and new hatchlings have significantly more predators, including crabs, small marine mammals and shorebirds.^[6] Additionally, their eggs are vulnerable to predation by scavengers like red foxes and golden jackals.^[77]

Green sea turtles have a variety of parasites including barnacles, leeches, protozoans, cestodes, and nematodes. Barnacles attach to the carapace, and leeches to the flippers and skin of the turtles, causing damage to the soft tissues and leading to blood loss. Protozoans, cestodes and nematodes lead to many turtle deaths because of the infections in the liver and intestinal tract they cause. The greatest disease threat to the turtle population is fibropapilloma, which produces lethal tumor growth on scales, lungs, stomach, and kidneys. Fibropapilloma is caused by a herpesvirus that is transmitted by leeches such as Ozobranchus branchiatus, a species of leech which feeds almost entirely on green sea turtles.^[63][78]

Life cycle

Green sea turtles migrate long distances between feeding sites and nesting sites; some swim more than 2,600 kilometres (1,600 mi) to reach their spawning grounds. Beaches in Southeast Asia, India, islands in the western Pacific, and Central America are where green sea turtles breed.^[7] Mature turtles often return to the exact beach from which they hatched. Females usually mate every two to four years. Males, on the other hand, visit the breeding areas every year, attempting to mate.^[79] Mating seasons vary between populations. For most C. mydas in the Caribbean, mating season is from June to September.^[25] The French Guiana nesting subpopulation nests from March to June.^[39] In the tropics, green turtles nest throughout the year, although some subpopulations prefer particular times of the year. In Pakistan, Indian Ocean turtles nest year-round, but prefer the months of July to December.^[54]

Sea turtles return to the beaches on which they were born to lay their own eggs. The reason for returning to native beaches may be that it guarantees the turtles an environment that has the necessary components for their nesting to be successful. These include a sandy beach, easy access for the hatchlings to get to the ocean, the right incubation temperatures, and low probability of predators that may feed on their eggs. Over time these turtles have evolved these tendencies to return to an area that has provided reproductive success for many generations. Their ability to return to their birthplace is known as natal homing.^[80] The males also return to their birthplaces in order to mate. These males that return to their homes know they will be able to find mates because the females born there also return to breed. By doing this, the green sea turtles are able to improve their reproductive success and is why they are willing to expend the energy to travel thousands of miles across the ocean in order to reproduce.

Mating behaviour is similar to other marine turtles. Female turtles control the process. A few populations practice polyandry, although this does not seem to benefit hatchlings.^[81] After mating in the water, the female moves above the beach's high tide line, where she digs a hole 28–56 centimetres (11–22 in) in depth with her hind flippers and deposits her eggs. The hole is then covered up again.^[82] Clutch size ranges between 85 and 200, depending on the age of the female. This process takes about an hour to an hour and a half. After the nest is completely covered, she returns to the sea. The female will do this 3 to 5 times in one season.^[7]

The eggs are round and white, and about 45 mm (1.8 in) in diameter. The hatchlings remain buried for days until they all emerge together at night.^[82] The temperature of the nest determines the sex of the turtles at around the 20–40 day mark. Green Sea Turtles are type 1a, meaning males develop at cooler temperatures while females are produced under hot temperatures.^[83][84] At around 50 to 70 days,^[85] the eggs hatch during the night, and the hatchlings instinctively head directly into the water. This is the most dangerous time in a turtle's life. As they walk, predators, such as gulls and crabs, feed on them. A significant percentage never make it to the ocean. Little is known of the initial life history of newly hatched sea turtles.^[25] Juveniles spend three to five years in the open ocean before they settle as still-immature juveniles into their permanent shallow-water lifestyle.^[65][66] It is speculated that they take twenty to fifty years to reach sexual maturity. Individuals live up to eighty years in the wild.^[6] It is estimated that only 1% of hatchlings reach sexual maturity.

Each year on Ascension Island in the South Atlantic, C. mydas females create 6,000 to 25,000 nests. They are among the largest green turtles in the world; many are more than 1 metre (3 ft 3 in) in length and weigh up to 300 kilograms (660 lb).^[86]

Breathing and sleep

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 permit a rapid exchange of oxygen and prevent gases from being trapped during deep dives. Sea turtle blood can deliver oxygen efficiently to body tissues even at the pressures encountered during diving. During routine activity, green and loggerhead turtles dive for about four to five minutes, and surface to breathe for one to three 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 quickly drown in shrimp trawlers and other fishing gear.^[31] During the night while sleeping and to protect themselves from potential predators, the adults wedge themselves under rocks below the surface and under ledges in reefs and coastal rocks. Many green sea turtles have been observed in returning to the same sleeping location night after night.^[34]

Threats

Human action presents both intentional and unintentional threats to the species' survival. Intentional threats include continued hunting, poaching and egg harvesting. More dangerous are unintentional threats, including boat strikes, fishermen's nets that lack turtle excluder devices, pollution and habitat destruction. Chemical pollution may create tumors;^[103] effluent from harbors near nesting sites may create disturbances; and light pollution may disorient hatchlings. With chemical pollution present, there is a development of tar balls that is often eaten by green sea turtles in a confusion of their food. Tar balls cause the green sea turtle to ingest toxins that can block their guts and cause swelling of the tissue, displacing the liver and intestines.^[104] Habitat loss usually occurs due to human development of nesting areas. Beach-front construction, land "reclamation" and increased tourism are examples of such development.^[6][9] An infectious tumor-causing disease, fibropapillomatosis, is also a problem in some populations. The disease kills a sizeable fraction of those it infects, though some individuals seem to resist the disease.^{[23][105][106]} In addition, at least in the Southwestern Atlantic (Río de la Plata, Uruguay), exotic invasive species such as the rapa whelk Rapana venosa, were reported massively bio-fouling immature green turtles, reducing buoyancy, increasing drag, and causing severe injuries to the carapace.^[107] Because of these threats, many populations are in a vulnerable state.

Pacific green turtles' foraging habitats are poorly understood and mostly unknown.^[108] These foraging grounds are most likely along the coast of Baja California, Mexico and southern California,^[109] in which these turtles have a high risk of incidental capture by coastal fisheries. The main mortality factor for these turtles is the shrimp trawlers in Mexico, in which many of these turtles go undocumented.^[109] The only foraging area that has been identified is San Diego Bay, but it is heavily polluted with metals and PCBs.^[109] These contaminants have a negative effect on the ocean environment, and have been shown to cause lesions and sometimes mortality.^[109] Green turtles also are threatened by entanglement and ingestion of plastic.^[109] In San Diego Bay, an adult green turtle was found dead with monofilament netting tightly packed in its esophagus.^[109] In addition there are indications that global climate change is affecting the ability of green turtle populations in Australia to produce males due to their temperature-dependent sex determination and the rising temperatures in the northern Great Barrier Reef region.^[110] Construction of new thermal power stations can raise local water temperature, which is also said to be a threat.^[111]

Green sea turtles are the most commonly traded species along Java's south coast and are sold in the form of whole, stuffed animals or turtle oil, locally known as "minyak bulus".^[112]

The geographer James J. Parsons' book titled The Green Turtle and Man played a special role in the conservation movement to save the species from extinction.^[113]

Global initiatives

The International Union for Conservation of Nature (IUCN) has repeatedly listed green sea turtles in its Red List under differing criteria. In 1982, they officially classified it as an endangered species.^[114] The 1986,^[115] 1988,^[116] 1990,^[117] 1994,^[118] and the landmark 1996 edition of the IUCN Red List, retained the listing.^[119]

In 2001, Nicholas Mrosovsky filed a delisting petition, claiming some green turtle populations were large, stable and in some cases, increasing. At the time, the species was listed under the strict EN A1abd criteria. The IUCN Standards and Petitions Subcommittee ruled that visual counts of nesting females could not be considered "direct observation" and thus downgraded the species' status to EN A1bd—retaining the turtle's endangered status.^[120]

In 2004, the IUCN reclassified C. mydas as endangered under the EN A2bd criteria, which essentially states the wild populations face a high risk of extinction because of several factors. These factors include a probable population reduction of more than 50% over the past decade as estimated from abundance indices and by projecting exploitation levels.^[1]

On 3 May 2007, C. mydas was listed on Appendix I of the Convention on International Trade in Endangered Species (CITES) as a member of the family Cheloniidae.^[121] The species was originally listed on Appendix II in 1975. The entire family was moved to Appendix I in 1977, with the exception of the Australian population of C. mydas. In 1981, the Australian population joined the rest. The Appendix I listing prohibits commercial international trade in the species (including parts and derivatives).^[122] The Zoological Society of London has listed the reptile as an EDGE species.^[123]

The Mediterranean population is listed as critically endangered.^[6][21] The eastern Pacific, Hawaiian and Southern California subpopulations are designated threatened. Specific Mexican subpopulations are listed as endangered. The Florida population is listed as endangered. The World Wide Fund for Nature has labeled populations in Pakistan as "rare and declining".^[55]

Since 1999, the Florida Aquarium has led extensive sea turtle rehabilitation efforts and visitor and community education & conservation platforms to advance sea turtle protection. Over a 20-year period, the aquarium received 200 sea turtles, and while not all could be released due to the nature of their injuries or illnesses, 180 were successfully released. In 2019, they opened a state-of-the-art Sea Turtle Rehabilitation Center in Apollo Beach, Florida. In the first year, The Florida Aquarium Animal Response Team managed the care of 21 sea turtles, initiated new foraging-readiness testing for release candidates in deep-dive tank, and released 14 animals. In 2020, they also initiated a study to better understand how micro-plastics are impacting the sea turtles in their care. In 2016, Florida enacted extensive protection measures. Florida statutes (F.A.C. Rule 68E-1) restrict the take, possession, disturbance, mutilation, destruction, selling, transference, molestation, and harassment of marine turtles, nests or eggs. Protection is also afforded to marine turtle habitat. A specific authorization from commission staff is required to conduct scientific, conservation, or educational activities that directly involve marine turtles in or collected from Florida, their nests, hatchlings or parts thereof, regardless of applicant's possession of any federal permit.

In the State of Hawaii, specifically on the Island of Hawai'i (Hawaii County), state representative Faye Hanohano, a Native Hawaiian rights activist, pressed for a measure to delist C. mydas from protected status so that Native Hawaiians could legally harvest the turtles and possibly their eggs as well. The bill, HCR14, was largely overlooked by the media since at that point it was only a local issue. While the bill was passed in the United States House of Representatives, the United States Senate's Committee on Energy and Environment refused to hear it, which meant that the bill did not go on to be heard by the Senate.^[124]

Country-specific initiatives

In addition to management by global entities such as the IUCN and CITES, specific countries around the world have undertaken conservation efforts.

The Indonesian island of Bali has traditional uses that were considered sustainable, but have been questioned considering greater demand from the larger and wealthier human population. The harvest was the most intensive in the world.^[92] In 1999, Indonesia restricted turtle trade and consumption because of the decreasing population and threat of a tourist boycott. It 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 wanted a smaller quota.^[125]

Multiple protected areas of the Philippines have significant green sea turtle nesting and feeding sites. The most notable is Turtle Islands Wildlife Sanctuary, an UNESCO tentative site which encompasses an entire municipality and one of Southeast Asia's most important green sea turtle nesting sites.^[126] Other notable sites include the UNESCO tentative site of El Nido-Taytay Management Resource Protected Area and the UNESCO World Heritage Site of Tubbataha Reefs Natural Park. The species is protected under Republic Act 9147 or the Wildlife Resources Conservation and Protection Act, while the sites where they live and nest are protected under the National Integrated Protected Areas System Act.^[127]

Ecotourism is one initiative in Sabah, Malaysia. The island of Pulau Selingan is home to a turtle hatchery. Staff people place some of the eggs laid each night in a hatchery to protect them from predators. Incubation takes around sixty days. When the eggs hatch, tourists assist in the release of the baby turtles into the sea.^[128]

The Hawaiian subpopulation has made a remarkable comeback and is now one focus of ecotourism 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.^[23]

In the United Kingdom the species is protected by a Biodiversity Action Plan, due to excess harvesting and marine pollution.^[129] The Pakistani-branch of the World Wide Fund for Nature has been initiating projects for secure turtle hatching since the 1980s. However, the population has continued to decline.^[9]

In the Atlantic, conservation initiatives have centered around Caribbean nesting sites. The Tortuguero nesting beaches in Costa Rica have been the subject of egg-collection limits since the 1950s. The Tortuguero National Park was formally established in 1976, in part, to protect that region's nesting grounds.^[36] On Ascension Island, which contains some of the most important nesting beaches, an active conservation program has been implemented.^[130] Karumbé has been monitoring foraging and developmental areas of juvenile green turtles in Uruguay since 1999.^[131]

In Mozambique, there are a number of initiatives to protect sea turtles. In the Primeiras e Segundas, WWF Mozambique has established a turtle tagging and protection program. The archipelago is a vital nesting area for green turtles, including Ilha do Fogo where Fire Island Conservation^[132] manage a turtle monitoring programme, and at Celdeira Island, where several nesting females have been tagged.

Cayman Turtle Farm located in Grand Cayman in the northwest Caribbean Sea is the first farm to have achieved the second generation of green sea turtles bred, laid, hatched, and raised in captivity.^[133] Since its beginning in 1968, the farm has released over 31,000 turtles into the wild,^[97] and each year more captive-bred turtles are released into the Caribbean Sea from beaches around the island of Grand Cayman.^[134] Captive-bred turtles released from the farm as hatchlings or yearlings with "living tags," have now begun to return to nest on Grand Cayman as adults.^[135][136] On February 19, 2012 the farm released the first 2nd-generation captive-bred green sea turtle equipped with a Position Tracking Transponder, or PTT^[137] (also known as a satellite tag).^[138] In addition, the farm provides turtle meat products to the local population for whom turtle has been part of the traditional cuisine for centuries. In so doing, the farm curtails the incentive to take turtles from the wild,^[139] which over the years in addition to the Cayman Turtle Farm's release of captive-bred turtles has enabled an increase in the number of turtles sighted in the waters around the island of Grand Cayman and nesting on its beaches.^[140]

In the Pacific, green sea turtles nest on the motu (islets) in the Funafuti Conservation Area, a marine conservation area covering 33 square kilometers (12.74 square miles) of reef, lagoon and motu on the western side of Funafuti atoll in Tuvalu.^[141]

On Raine Island, up to 100,000 nesting females have been observed in a season, with the cay producing 90% of the region's green turtles. However, the hatching rate declined in the 1990s, and a further decline in the population was threatened by the deaths of thousands of females as they struggled to climb the small sandy cliffs. In addition, as the shape of the island had changed over time, the spread of the beaches outwards had led to greater risk of inundation of the turtle nests. Between 2011 and 2020, a collaborative project by the Queensland Government, BHP (as corporate sponsor), the Great Barrier Reef Marine Park Authority, Great Barrier Reef Foundation, and Wuthathi and Meriam traditional owners, reshaped the island using heavy machinery in a way that gave the female turtles a smoother passage and reduced the risk of nest inundation. A sophisticated monitoring and research system, using 3D modelling, satellite technology and drones was employed, and monitoring continues.^[142]

As of June 2020^[update], a project called "The Turtle Cooling Project" is being undertaken by scientists from the World Wildlife Fund Australia, University of Queensland, Deakin University and the Queensland Government. It is looking at the effect of global warming on northern green turtle breeding, in particular the effect of producing more male turtles owing to the higher temperatures. They are working in the area around Raine Island, Heron Island and Moulter Cay.^[143]