The largest of all the sea turtle species (and the largest living reptile) – the leatherback turtle (Dermochelys coriacea) – owes its name to its unique shell, which is composed of a layer of tough, rubbery skin strengthened by a matrix of thousands of tiny bone plates that look almost like a jigsaw puzzle. It is the only marine turtle without a hard carapace and without claws on its flippers.
The leathery, dark grey to black carapace is mottled with white spots and marked by five ridges; the plastron is cream to black in colour. The leatherback’s body is teardrop-shaped and tapers at the hind end to a blunt point.
The shape of its shell makes it very hydrodynamic. Mature males and females can grow to over 2 metres in length and weigh up to 900 kg, although individuals of this size are rarely seen today. Leatherbacks mature between 8 and 15 years of age and are estimated to have a life span of around 45 years in the wild, but this is not well documented.
Leatherback Turtle Biology and Behaviour
Leatherbacks have a patch of pink skin on the top of their heads. Each spot, like our fingerprint, is unique. Scientists are not sure about the function of this spot but it might help the turtle sense light or determine where it is geographically.
Like all marine turtles, leatherbacks do not have teeth. Instead, they have two pointed cusps on their upper jaw and one on their lower jaw to help grasp their prey. Additionally, the leatherback’s oesophageal tract is lined with sharp, downward pointing spines. These are thought to prevent prey from escaping once caught, and to help shred food before it reaches their stomach.
Unlike other sea turtle species, female leatherback turtles may use different nesting beaches from year to year (though they tend to stay in the same region). Because of their size, females prefer open-access beaches with a deep-water approach and soft sand. Leatherbacks usually nest once every 2 to 3 years and from 6 to 9 times per season. Females leave track marks about 150-200 cm wide, with symmetrical flipper marks and a deep median tail groove.
Laying a nest takes the female from 1.5 to 2 hours, as she is extremely slow and clumsy on land. A clutch consists of an average of 80-100 fertilised eggs, covered by a layer of about 30 smaller, unfertilised eggs. Scientists are not sure about the function of these yolkless eggs, but they think that they might prevent sand from falling between the fertile eggs, which allows more oxygen to circulate around them. Incubation takes about 65 days.
Upon hatching, the baby turtles are around 50-75 mm long and they are black with white along the flipper margins and the ridges down their back.
Leatherback Turtle Diet
Leatherback turtles have delicate, scissor-like jaws, and feed exclusively on soft-bodied animals. A leatherback’s diet consists almost entirely of jellyfish, but they may also eat salps; gelatinous free-swimming marine invertebrates with transparent barrel-shaped bodies. They rarely feed on tunicates and cephalopods such as squid and octopus. This type of turtle can eat around 73% of its own body weight in jellyfish every day, packing in around 16,000 calories. That is around 3 to 7 times more than they actually need to survive and allows them to fuel their long migrations.
Leatherback Turtle Habitat and Distribution
Leatherback turtles are the most migratory and wide-ranging of all marine turtles and may have the widest global distribution of any vertebrate species on the planet. They are found throughout the Atlantic, Pacific, and Indian Oceans, from the Gulf of Alaska to the waters of Tasmania.
The leatherback turtle is the least common turtle species in the Indian Ocean. Yet important nesting populations exist in Indonesia, South Africa, Sri Lanka, and India’s Andaman and the Nicobar Islands. Some of the most important nesting beaches in the Nicobar Islands, which used to host 400-600 nesting females per year, were destroyed by the 2004 tsunami. They are now showing signs of recovery. From 100 to 200 turtles are estimated to nest annually in Sri Lanka.
Leatherbacks are powerful swimmers and regularly travel enormous distances, crossing entire ocean basins. However, very little information is available on the movements of leatherbacks in the Indian Ocean.
Mostly pelagic in nature, leatherback turtles are also known to forage in temperate coastal waters. They travel from their tropical breeding and nesting grounds to find their favourite prey: jellyfish.
Scientists have a poor understanding of the distribution and developmental habitats of juvenile leatherbacks. However, it is thought that they remain in coastal tropical waters (above 26°C) until reach about one metre in length. Sightings of juvenile leatherback turtles are very rare.
The leatherback’s pelagic habits make it especially at risk of interactions with fisheries, particularly longlines. Additionally, leatherback turtles cannot swim backwards. This means that once they become entangled in a net or line, they have little chance of escaping from it.
Leatherback turtles can dive to depths of over 1,200 m, much deeper than any other marine turtle. They can stay down for up to 85 minutes, though a typical dive only lasts 3 to 8 minutes.
Leatherback Turtles in the Maldives
In the Maldives, this turtle is known as “musimbi”, which means Mozambique, and sightings are very rare. No nesting events have been confirmed in the last 100 years.
IUCN Red List Status: Vulnerable (2013)
Global population estimate: 30-40,000 adult females in 1996.
Sources: Hudgins, Ali, and Mancini (2017) “Marine Turtles of the Maldives: A field identification and conduct guide”. An IUCN Publication funded by USAID.