Green Turtle

Body depressed in adults, carapace oval in dorsal view, its width about 88% of its length. Head relatively small and blunt, about 20% of the carapace length, one pair of elongated prefrontal scales between the orbits; tomium of lower jaw with a sharply serrated, cutting rim that corresponds with strong ridges on the inner surface of the upper tomium, which loses its tip cusp with age. The carapacial scutes are thin, smooth and flexible when removed. Those of the dorsal side include 4 pairs of lateral scutes, the foremost not touching the precentral scute; 5 central scutes, low-keeled in juveniles, but lacking a median keel in subadults and adults; and usually 12 pairs of marginal scutes- On the underside, the scutes are also smooth and rather thin and comprise 4 pairs of inframarginal, 12 pairs of central plastral, usually one intergular and sometimes one interanal scute. Each flipper has a single visible claw. Colour: On the upper side, the general appearance varies from pale to very dark and from plain colour to brilliant combinations of yellow, brown and greenish tones, forming radiated stripes, or abundantly splattered with dark blotchesThe Pacific populations are more melanistic than the Atlantic ones. In juveniles, the scales of the head and upper sides of the flippers are fringed by a narrow, clear, yellowish margin that is lost with age. Underneath, the Atlantic forms are plain white, dirty white or yellowish white; the Pacific forms are a dark greybluish-green. The newborn hatchlings are dark brown or nearly black on the upper side, the carapace and the rear edges of the flippers with a white margin. Underneath they are white.

Widely distributed in tropical and subtropical waters, near continental coasts and around islands, rare in temperate waters . Together with the hawksbill (Eretmochelys), the green turtle is the most tropical of the marine turtles. Its normal latitudinal range remains within the northern and southern limits of the 20°C isotherms, and follows the seasonal latitudinal changes of these limits. In summer, the limits are about 40°N and 3S°S on the western sides of the oceans, and somewhat more contracted (to 30°N and 25°S) on the eastern sides. During winter, they descend to 30°N and 25°S or less in the western sides, and to 20°N and 15°S or less in the eastern sides. Occasionally, some turtles overwinter outside the above-mentioned latitudinal limits, as in Chesapeake Bay on the east coast of the USA. Also outside the normal range there are many records of solitary individuals, all of them in non-reproductive stages. These stragglers reach higher latitudes in the north than in the south.

The size of turtles is principally related to the carapace length, which is considered a reliable measure of overall size. Measurements over the carapace curve (CCL) in adults are 3 to 4 cm larger than straight carapace length (SCL). The available data sometimes do not indicate in which way the measurements were done, and in such cases the information must be used as a reference of relative value, bearing in mind that such records could be biassed by up to 4%. Because of their presence on the nesting beaches, size reports on females are more common than those on males. [more...]

Ch. mydas is a typical solitary nektonic animal that occasionally forms feeding aggregations in shallow water areas with abundant seagrasses or algae.This species migrates from rookeries to feeding grounds, which are sometimes several thousand kilometers away. Nearly all migrations are performed along the coasts, but some populations, e.g. those at Ascension Island, carry out transoceanic migrations of more than 2 200 km from this island, where they nest, to the coast of Brazil where the feeding grounds are located (Carr, 1962, 1975). The major nesting grounds are always found in places with seawater temperatures mainly over 25°C. The most important nesting beaches for the Atlantic population are as follows: Tortuguero, Costa Rica and Aves Island, Venezuela; Bigisanti, Eilanti and Baboensanti, Suriname; several beaches from Para to Sergipe, in Brazil; Ascension Island and Cape Verde Islands. In the Mediterranean Sea, small colonies nest in several beaches off the southern coast of Turkey: Mersin, Side, Belek, and also on Cyprus Island, where single nestings occur on the eastern coast. In the Western Indian Ocean, nesting occurs at Europa Island, the Comoro Islands (Moheli), Seychelles, Tromelin and Mascarenes Islands; Democratic Republic of Yemen (Mukalla, Shihr); northeast of Oman and Masira Island. In the Western Pacific Ocean, nests have been recorded from the southeast coast of Malaysia and offshore islands; Sarawak, Satang and Talang Islands; Philippines ("Turtle Islands", the Sulu Sea, Pulau Boaan, Baguan, Taganak, Bakkungan, Palawan); Australia (Lacepède Islands); Gulf of Carpentaria, Rayne Island, Pandora Cay, Capricorn Group, including Heron Islands and Bunker Group with Hoskyn Island. In the Central Pacific, nesting occurs on hundreds of islands, but there is no comprehensive study that could show their status and the specific boundaries of the populations. Because of the wide distributional range of the species, the nesting season varies in time among distant and near localities. The available information on nesting seasons is very disperse, and two or more authors often quote different periods for the same localities. Such information makes it more difficult to prepare comprehensive nesting calendars by latitudes; hence, the available data are here compiled by geographical areas, e.g.: Caribbean Sea, from April to October, with the peak between June and September (Belize, Cayman Islands, Cuba, Tortuguero - Costa Rica) Northwestern Atlantic Ocean, from May to October, with the peak between June and August (eastern Florida). Gulf of Mexico, from May to September, with a peak between June and August (Tamaulipar, Campeche, Yucatan and Quintana Roo). Southwestern Atlantic Ocean, throughout the year, with peaks from March to September (April - May in Surinam, July - August in French Guiana and September in Colombia). Southeastern Atlantic Ocean, from November to February (Gulf of Guinea) and February - April (Ascension Island). Western Indian Ocean, throughout the year, with peaks from February to April (Aldabra Islands), from May to August (Seychelles, Comoro Archipelago) and from November to February (Reunion and Eparses Islands). Northwestern Indian Ocean, from May to October beginning in Saudi Arabia, and onwards from August in Oman and Masira Island. Central Indian Ocean, from July to March, starting in southeast India and ending in the Maldive and Laccadive Islands. Eastern Indian Ocean, with a very long season, and several peaks, from May to August (Andaman - Nicobar Islands, Thailand and Western Malaysia), from June to November (Burma). Western Pacific Ocean, throughout the year, with peaks from November to April (Western Indonesia); from March to September (Southern Japan, in June to July; China, Philippines and Papua New Guinea, in July - August) and from September to April (Sabah, Palau, Bismark Archipelago, Turks Islands). Central Pacific Ocean, throughout the year, with peaks from September to February (New Caledonia, New Hebrides, Tonga, Samoa, Tokelau Islands), from June to August (Marshall islands), from November to February (northern and northeastern Australia), from June to August (Hawaii -French Frigate Shoals) and from September to December (Society, Tuamotu and French Polynesia Islands). Females usually show nesting site fixity, and they are able to return to lay eggs near the same spot where they left the last clutch or even on the same beach from which they emerged as hatchlings. The interval between successive seasonal nesting migrations depends on population, feeding ground quality and remoteness. Usually there is a two-year breeding interval, but the turtles may breed in cycles of one, 3 or 4 years, or switch from one to another cycle, as a result of ageing or external influences (food quality and quantity). The successive nestings within the same season are separated by intervals of about two weeks. The majority of green turtles lay between 2 and 5 clutches, others lay only once or more than 5 times, the average of the colony, during the season, being usually slightly over 2.5 times per female. The mean clutch size ranges from 84.6 eggs (in the Solomon islands) to 144.4 eggs (in southeast Africa). This quantity also varies with age and size of the turtle, time of the season, distance of migration, etc.; the minimum and maximum records are 38 and 195 eggs per clutch, in South Yemen and Ascension Island respectively. Minimum and maximum egg sizes recorded are 38 and 58-7 mm, with averages of 42.3 and 54.6 mm (South Yemen and Ascension Island respectively); the minimum and maximum weight records for egg masses are 38.1 and 60.4 g (Southeast Africa and Australia respectively), with averages of 47.7 and 52.9 9 (Southeast Africa and Comoro Island respectively). Hatchlings also show variations in size and weight among populations; the records for carapace length are between 44 and 59 mm, with mean lengths of 46.9 and 54 mm (South Yemen and Northeast Australia); the minimum and maximum body weight records are 18.4 and 35 9 (Southeast Africa and Hawaii) and the averages are 21.6 to 31 g (Comoros, French Polynesia and Hawaii). There are many speculations about the age at first maturity. It has been estimated as low as 6 years by some authors, and between 8 and 13 or more years, by others. New studies using the average instead of the smallest sizes of nesting turtles, have produced estimates ranging between 25 and 30 or more years (Florida, Hawaii and Australia). Of course, the size and age at which the sexual maturity is reached, show variations among individuals of the same population, and the differences are more remarkable when comparing isolated populations. In captivity, green turtles reach 35 kg in about 3 years (Cayman Turtle Farm, on Cayman Islands) and start to reproduce in less than 10 years. Reproduction involves courtship, copulation and nesting. A single female, usually near shore, is courted by several males; copulation begins early in the breeding season and stops when nesting begins; usually the females avoid mating after they have laid the first clutch. It is hypothesized that fertilization of the eggs laid in any nesting season takes place several years before, and that the last "encounter" between males and females probably serves to fertilize eggs for the next season. New studies with turtles in captivity show that fertilization occurs early in the season and that excess sperm is probably stored and used in the fertilization of later clutches, and there may even be enough sperm for some clutches of the next season. Apparently there are no variations among hatch rates of successive clutches within a season, but certainly some females have higher or lower rates of fertility, and a few are infertile. Egg incubation on the sand beach normally extends from 48 to 70 days; the duration of the incubation is related to temperature and humidity which change in the course of the season; hence it will be longer in cool weather conditions. Hatching and emergence occur mostly at night and stop when the sand becomes hot. The hatchlings emerge from the nest simultaneously, race quickly to the surf and swim frenziedly toward the open sea. The colour of the hatchlings, black above and white below, is probably an adaptation to nektonic life at the water surface and makes the turtle less conspicuous to fish and bird predators. There is high predation throughout the life-cycle of green turtles, the eggs are consumed by mammals such as raccoons, skunks, opossums, mongooses, coatis, domestic pigs, dogs and also jaguars, and by other animals like the monitor lizards (Varanus), ghost crabs, ants, fly maggots, etc. Some hatchlings are invaded by ants, maggots and mites immediatly after- they pip the egg-shells, or by crabs, mammals and birds, when they reach the nest surface; in the water, the main predators are sea birds and carnivorous fishes, e.g., hatchlings were recovered from the stomachs of a dolphin fish (Coryphaena hippurus), and from groupers (Epinephelus (Promicrops) lanceolatus) which are capable of devouring entire juvenile green turtles in the South Pacific. This predation continues until the turtle reaches a size big enough to avoid being swallowed- Sharks are the most formidable enemy throughout the life-cycle of green turtles. In the sea, invertebrates such as leaches (Ozobranchius branchiatus and 0. marggoi), invade the epithelial areas of the body, especially near to the cloacal opening, eyes, axils, etc. causing necrosis, and it is reported that heavy infestations can produce a kind of papillomatosis. This species, and the black turtle (Chelonia agassizii), in adulthood, are the only herbivorous sea turtles, but in captivity, both can be maintained on a carnivorous diet. Feeding behaviour in the young stages, from hatchlings until juvenile size, is nearly unknown, but it is assumed that they are carnivorous - which ensures them fast growth rates and when they get enough weight and size to avoid most predators, they progressively shift to a herbivorous diet- The mechanisms and time required to become strictly herbivorous are unknown, but for example, in all of the 18 green turtles of 7.8 to 54.5 kg studied in Mosquito Lagoon, Florida, seagrasses (Syringodium, Diplantera and Halophila) made up 86.5% + /- 10.6 of the wet biomass of the stomach contents; also, the stomach contents of 94 green turtles between 31 and 120 cm of carapace length from the commercial catch off the coast of Ceara, Brazil (1965-67), included from 88.3% to 95.5% of bentic algae, and the remainder was made up of small quantities of phanerogams, sponges, bryozoans, crustaceans, sea urchins, molluscs and sea squirts. Green turtles feed during day-time in the seagrass beds that grow in shallow waters. These feeding grounds are apparently not much used by other vertebrates, except for sirenians, but usually these mammals and the green turtles have minimal overlapping distribution. Some fishes, molluscs and other invertebrates also live on these seagrass beds, but their grazing is not significant compared to that of the green turtle. Among the major forage items of adult green turtles are the seagrasses Zoostera, Thallasia, Cymodocea, Syringodium, Diplantera, Halodule and Halophila, and the algae Gelidium, Gracillaria, Gracilliaropsis, Hypnea, Caulerpa, Vidalia, Bryothamnion, Cryptonemia, Agardiella, etc. Together with this vegetarian food, small quantities of animals living in these meadows are ingested indirectly but they usually represent less than 2% of the total dry weight of the stomach contents.

The main commercial fishing gear used to catch green turtles are: entangling nets, drift-nets, harpoons, grapnels, hooks and also "turning nesting females onto their backs". Green turtles are often taken as bycatch in shrimp trawls, set-nets, gill-nets and beach seines, and sometimes juveniles are captured with cast-nets. Other common methods are spear-gunning by scuba divers, and following turtles closely in shallow waters until they get tired and are hauled up to the boat. Finally, an interesting method of turtle hunting is the use of the "living fish hook", the sucking fish or remora, that was common in the Caribbean Sea, in Chinese waters, Torres Straits and some other south Asian localities. The major "Fishing Areas" for green turtles correspond to the sites of important rookeries and feeding grounds already mentioned in the former chapter, and capture may be increased during the breeding season. Meat is the principal product obtained from the green turtle, and the yield per animal ranges from 20 to 25% of its total live weight. Other products are calipee and calipash. Oil is obtained from the green or yellowish fat. Green turtle eggs are obtained either from the butchered turtle or directly from the nesting beaches. The green turtle is considered the best species for commercial farming or ranching. International commerce of wild green sea turtles is forbidden, but capture for use as a food for local consumption persists in many central Pacific Islands, in Southeast Asia and Indonesia, Indian Ocean islands and mainland coasts, east coasts of Africa and Arabian peninsula, South America (northeastern countries, Caribbean islands), Mexico and Central America (Atlantic-side countries). All those places have had variable levels of green sea turtle exploitation and some of them were historically important fresh-meat exporters. The FAO Yearbook of Fishery Statistics reports only data for Fishing Area 31 (Western Central Atlantic, 359 t in 1987 of which 291 correspond to Cuba), and Fishing Area 71 (Western Central Pacific, 46 t, Fiji only). The total reported catch of Chelonia mydas in recent years was: in 1982: 409 t, in 1983: 432 t, in 1984: 279 t, in 1985: 712 t, and in 1986: 428 t. The United States imports of turtle meat and calipee were registered up to the 1970's, but since 1978-1979, they were mostly replaced by Cayman Turtle Farm products. European countries such as Switzerland, West Germany and the United Kingdom, also were importers up to the ban, proclaimed in the late 1970's, when they all signed the CITES resolutions prohibiting the commerce of wild sea turtle products. However, some of the countries that ratified the CITES, decided that trade with Cayman Turtle Farm products could continue (West Germany, United Kingdom, France, Italy, etc) but placed a reservation on green, ridley and hawksbill turtles. Finally, all these reservations became ineffective when the proposal to transfer sea turtles produced by farming or ranching from Appendix 1 to Appendix 11 was rejected at the last Conference of the Parties, held in Buenos Aires, Argentina on 3 May 1985. The total catch reported for this species to FAO for 1999 was 15 t. The countries with the largest catches were Cuba (8 t) and Grenada (5 t).