Green turtles (Chelonia mydas) are the largest of all the hard-shelled sea turtles. They can grow to about 120 cm in length and weigh between 135 and 160 kg. The green turtle has a smooth, sub-circular to heart-shaped carapace with colour varying from greenish-yellow to greyish-brown. The plastron is yellowish-white in colour. In the Maldives, the colouration of adults is darker than that of green turtles in the western Indian Ocean.
Green Turtle Biology and Behaviour
Green turtles reach adulthood between 15 and 50 years of age. Turtles that eat a diet rich in nutrients grow and mature faster than those with a poor diet.
Mature females return to their nesting beaches once every 2-4 years to nest. Females migrate huge distances between feeding grounds and nesting areas, but tend to follow coastlines rather than cross open waters. A female green turtle leaves a symmetrical track with a tail drag down the middle. Tracks are 85-90 cm across. The females lay between 1-6 clutches of between 70 and 125 eggs. Larger females tend to lay larger clutches of eggs. The incubation period lasts between 50 to 70 days.
Green turtle hatchlings measure around 50 mm long at birth. Their carapaces is black and they have a light coloured plastron.
Green Turtle Diet
Adult green turtles are vegetarians, feeding primarily on seagrasses and algae. The greenish coloured fat deposits under their carapaces is probably due to this diet, and the source of their name. Juvenile green turtles, however, feed on small crustaceans and jellyfish. As they mature, their diet shift from omnivorous to herbivorous.
Turtles actively select fresh green growth near the base of the seagrass and there is some evidence that turtles actively farm certain areas of seagrass to ensure a steady supply of younger, protein-rich growth. When seagrass pastures are absent, as they are in much of the Maldives, they eat other species of red and green algae.
Green Turtle Habitat and Distribution
The green turtle can be found worldwide in tropical and sub-tropical waters down to 20°C. They have been recorded as far north as the English Channel and as far south as Polla Island, Chile. Green turtles are highly migratory and as a result undertake complex migrations through graphically different habitats. Some times they migrate thousands of kilometres to lay their eggs.
Both males and females migrate from benthic foraging areas to mainland or island nesting beaches. The best feeding grounds rarely coincide with the best nesting beaches. Green turtles can travel 20-40 km per day when migrating.
Green turtles are not picky about their nesting beaches; sand size, composition, and the presence of beach vegetation do not seem to be factors in choosing a nesting site. Mating generally occurs around one kilometre offshore of nesting beaches.
Although nesting occurs in more than 80 countries worldwide, only 10-15 populations are of significant size (greater than 2,000 females yearly). The Indian Ocean is home to some of the largest nesting populations of green turtles in the world, particularly Oman, Pakistan, and Reunion Island. The nesting population of green turtles in the Maldives is currently unknown, but populations in India and Sri Lanka are severely depleted. Nesting appears to happen all year-round.
Green Turtle in the Maldives
In the Maldives, the green turtle is known as “velaa”. Both juveniles and adults forage on seagrass beds throughout the archipelago. Furthermore, they nest in several atolls, including Baa, North Male, Laamu, Noonu, Addu, and Lhaviyani. Previous reports have noted more nesting on the northern and eastern sides of the archipelago and a peak in nesting between June and December. Marine biologists and citizen scientists have photographed more than 150 individuals throughout the archipelago and green turtles seem to stay on their chosen “home reefs”, being seen year after year in the same spots. Most observed turtles at coastal foraging grounds are juveniles.
Green Turtle Conservation Status
IUCN Red List Status: Endangered (2004)
Current global population estimate: 203,000 breeding females
Sources: Hudgins, Ali, and Mancini (2017) “Marine Turtles of the Maldives: A field identification and conduct guide”. An IUCN Publication funded by USAID.