Green turtle (Chelonia mydas)
|French:||Tortue Comestible, Tortue Franche, Tortue Verte|
|Spanish:||Tortuga Blanca, Tortuga Verde|
|Size||Length: 80 - 150 cm (2)|
|Weight||65 - 136.2 kg (2)|
- Green turtles are named after the green colour of their fat.
- Some green turtle populations in Brazil migrate 2,250 km to get to breeding grounds on the Ascension Islands.
- Green turtle hatchlings have a special ‘egg tooth’ which they use to break out of the egg.
- Green turtles take between 26 and 40 years to become reproductively mature, the longest of any sea turtle.
The green turtle is classified as Endangered (EN) on the IUCN Red List (1), and is listed on Appendix I of CITES (3) and Appendices I and II of the Convention on Migratory Species (CMS or Bonn Convention) (4).
The green turtle (Chelonia mydas) is one of the largest and most widespread of all the marine turtles (5). The oval carapace varies from olive to brown, grey and black with bold streaks and blotches (6) (7), but the common name, green turtle, is derived from the green colour of the fat and connective tissues of this species (8). Two subspecies are traditionally recognised; the Pacific green turtle (Chelonia mydas agassizii) tends to be smaller than its Atlantic cousin (C. m. mydas) with a narrower carapace that may sometimes be completely black, providing the other common name of 'black turtle' to certain populations (7) (9). The plastron, or undershell, of the green turtle remains a pale yellow or orange throughout life (6). Males are generally smaller than females (10), and the green turtle differs in appearance from other marine turtles by the possession of a single pair of scales in front of the eyes and a serrated bottom jaw (8). The tiny black hatchlings are only around 5 centimetres long (7).
Found in tropical, and to a lesser extent subtropical, waters, the green turtle ranges throughout the Pacific, Atlantic and Indian Oceans, as well as in smaller seas such as the Arabian Gulf and the Mediterranean Sea (1) (11).
Normally inhabiting shallow developmental areas, rich in sea grass or marine algae, the green turtle migrates long distances every few years to the nesting beaches. Upon hatching, juveniles are thought to undertake an oceanic phase, where they possibly float passively on major current systems in the open ocean (1).
The green turtle has particularly slow growth rates and appears to take longer to become reproductively mature than any other sea turtle species, with age at sexual maturity ranging from 26 to 40 years (1). Undertaking tremendous feats of navigation, an adult green turtle will return to the same beach to breed each season. Astonishingly, part of the population in Brazil migrates around 2,250 kilometres across the open ocean to breed on the Ascension Islands (12). Mating tends to occur just offshore of the nesting beaches, with the male green turtle using a curved claw on each front flipper and a flat nail at the end of the tail to grip the female (8). The female hauls out onto the beach at night and digs a large nest with the back flippers beyond the high tide mark, typically laying between 100 and 150 eggs before proceeding to cover the nest with sand (5) (7) (13). The female returns to breed only once every two to five years but will lay up to nine nests in that one season (8). Incubation takes between 45 and 70 days, and temperature has been shown to determine the sex of hatchlings; with females being produced at warmer temperatures (13). Breaking open the eggs with a special hooked 'egg tooth' that will subsequently be lost; hatchlings use their powerful front flippers to reach the surface, and then proceed to the sea. The soft-bodied juveniles are particularly vulnerable at this time from a variety of predators, such as ghost crabs and gulls on the beach to sharks and dolphins in the water (5) (14).
Unlike other marine turtles, the adult green turtle is almost exclusively herbivorous, grazing on sea grasses and algae (11), whilst the young are typically omnivorous, commonly feeding on jellyfish, molluscs and sponges (5).
The green turtle is overharvested in many areas for both its meat and eggs (11). The meat is highly prized and the cartilage underneath the plastron (known as 'calipee') is used in the production of turtle soup (8). In addition, the green turtle is affected by a number of incidental threats, including fisheries bycatch, habitat degradation, and disease. Building construction, beach armouring and sand extraction are responsible for degradation of nesting habitat, while light pollution at nesting beaches fatally attracts emerging green turtle hatchlings away from the sea. In the marine environment, increased effluent, over harvesting of algae, and contamination from coastal development all negatively affect the quality of foraging habitat. In particular, the degradation of marine habitats is implicated in the increase of fibropapillomas; fibrous tumours that can grow on almost any part of a turtles body, impeding movement or sight, and often leading to death (1).
The green turtle is protected by a raft of international legislation including the prohibition of international trade through its listing on Appendix I of CITES (1) (3). The result of numerous designations and agreements has been to notably reduce the intensity of direct impacts on the green turtle and, in particular, the rate at which eggs and adults are harvested. Nonetheless, human impacts on the green turtle are still a significant concern, with the lack of effective monitoring of fisheries responsible for considerable direct and indirect mortality, while uncontrolled development continues to degrade the ecosystems that the green turtle depends on (1).
For more information on green turtles and their conservation see:
Marine Turtle Newsletter:
Authenticated (11/10/02) by Brendan Godley, Marine Turtle Newsletter.
- Bycatch: in the fishing industry, the part of the catch made up of non-target species.
- Carapace: the top shell of a turtle. In arthropods (insects, crabs etc), the fused head and thorax (the part of the body located near the head) also known as ‘cephalothorax’.
- Molluscs: a diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.
- Omnivore: an organism that feeds on both plants and animals.
- Plastron: in reptiles, the ventral shell of a turtle or tortoise.
- Subspecies: a different race of a species, which is geographically separated from other populations of that species.
IUCN Red List (April, 2008)
South Atlantic Fishery Management Council (April, 2008)
CITES (April, 2008)
Convention on the Conservation of Migratory Species of Wild Animals (April 2008)
- Burnie, D. (2001) Animal. Dorling Kindersley, London.
- Spotila, J.R. (2004) Sea turtles: a complete guide to their biology, behavior, and conservation. John Hopkins University Press, Baltimore and London.
MarineBio (August, 2009)
- Ripple, J. (1996) Sea Turtles. Voyager Press, Stillwater, USA.
- Fritz, U. and Havas, P. (2007) Checklist of Chelonians of the World. German Federal Ministry of Environment, Nature Conservation and Nuclear Safety and Museum of Zoology Dresden, Bonn and Dresden.
- Godley, B.J., Broderick, A.C., Frauenstein, R., Glen, F. and Hays, G.C. (2002) Reproductive Seasonality and Sexual Dimorphism in Green Turtles. Marine Ecology Progress Series, 226: 125-133.
WWF (September, 2002)
- Zug, G.R., Vitt, L.J. and Caldwell, J.P. (2001) Herpetology. Academic Press, London.
- Godley, B. (October, 2002) Pers. comm.
The IOSEA Marine Turtle Memorandum of Understanding (August, 2009)