Green turtle  (Chelonia mydas)

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).

The UK Biodiversity Action Plan for this species is available at UK BAP.

Environment Agency - Abu Dhabi is a principal sponsor of ARKive. EAD is working to protect and conserve the environment as well as promoting sustainable development in the Emirate of Abu Dhabi.

View information on this species at the UNEP World Conservation Monitoring Centre.

To learn more about a Whitley Award-winning conservation project for this species, click here.

For more information on green turtles and their conservation see:

• Marine Turtle Newsletter:
  www.seaturtle.org/mtn/