Leatherback Sea Turtle (Dermochelys coriacea): Facts and Size

Appearance

A leatherback is shaped like a giant teardrop. The shell, or carapace, has no hard plates. Instead it is made of thousands of small, interlocking bones covered by thick, oily skin with the feel of rubber or leather, which gives the turtle its name. Seven ridges run lengthwise along the back, and the shell tapers to a point above the tail.

The skin is dark gray to black with scattered white or pinkish spots, and the underside is pale. Adults have a pink spot on top of the head, over a thin area of skull that lets light through to the brain, and scientists think it may help the turtle sense day length. The front flippers are enormous, the largest of any sea turtle compared with body size, and lack claws. Instead of teeth, the jaws have two sharp points on the upper beak, and the throat is lined with backward-pointing spines that keep jellyfish from slipping out.

Size: the largest living turtle

Adult leatherbacks commonly have a curved shell length of about 1.3 to 1.8 m (4.3 to 6 ft) and a total length of 1.8 to 2.2 m (6 to 7 ft). Most weigh between 250 and 700 kg (550 and 1,540 lb); nesting females in the Caribbean and French Guiana average around 340 to 390 kg (750 to 860 lb). In large individuals the front flippers span about 2.7 m (9 ft) from tip to tip.

Hatchlings, by contrast, are only about 6 cm (2.4 in) long and weigh around 45 g (1.6 oz). The famous “Harlech turtle,” a male found dead on a beach in Wales in 1988, was reported at 916 kg (2,019 lb), but those figures have since been questioned. The full story is in how big is a leatherback.

Habitat and range

Leatherbacks have the widest range of any reptile. They live in the Atlantic, Pacific and Indian oceans and enter the Mediterranean, ranging north to Norway, Newfoundland and Alaska and south to Chile, the tip of South Africa and New Zealand. Unlike other sea turtles, which mostly stay in warm water, adult leatherbacks regularly feed in cold seas, including the waters off Nova Scotia, Ireland, the UK and western France.

Their migrations are among the longest of any animal. Leatherbacks nesting in Papua, Indonesia, swim across the Pacific to feed on jellyfish off California and Oregon, and one tracked turtle covered about 20,000 km (12,000 mi) in 647 days. Females tagged in French Guiana have turned up off Spain and Morocco.

How leatherbacks survive in cold water

Most reptiles cannot stay active in cold water, but leatherbacks have been recorded feeding in water below 5 °C (41 °F), and their body temperature can be up to about 18 °C (32 °F) warmer than the sea around them. Scientists call this ability gigantothermy: a very large body loses heat slowly, especially when it is wrapped in a thick layer of oily fat.

Heat comes mostly from the muscles, because a leatherback swims almost constantly. Blood vessels in the flippers are arranged as countercurrent heat exchangers, in which warm blood flowing out passes close to cool blood flowing back and gives up its heat to it, so little warmth is lost through the flippers. The leatherback is not warm-blooded like a mammal, but it keeps its core temperature well above that of the water.

Diet: a jellyfish specialist

Leatherbacks eat almost nothing but gelatinous animals: jellyfish such as lion’s mane and moon jellyfish, along with salps, pyrosomes and siphonophores. Jellyfish are mostly water and very low in calories, so leatherbacks must eat huge amounts. Studies of turtles feeding off Nova Scotia estimated that an adult may eat jellyfish equal to more than half its body weight in a single day.

Because floating plastic bags and balloons can look and even smell like food, leatherbacks are among the sea turtles most at risk of swallowing plastic; see why do sea turtles eat plastic.

Diving

Leatherbacks dive deeper than any other turtle and most other air-breathing animals. Tagged turtles have reached depths of more than 1,000 m (3,300 ft), with the deepest widely cited record around 1,200 to 1,300 m (about 4,000 to 4,200 ft). Most dives are much shallower and last a few minutes to about a quarter of an hour, as the turtles follow jellyfish that move up and down in the water column. Learn more in how deep can leatherbacks dive.

Leatherbacks in European and North American waters

Many people are surprised to learn that the world’s largest turtle is a regular summer visitor to cold northern seas. Each year leatherbacks arrive off Nova Scotia, Newfoundland and New England, and in the eastern Atlantic off western France, Ireland, Wales, Cornwall and western Scotland, following blooms of lion’s mane, compass and barrel jellyfish. They are seen most often from July to October, sometimes close to shore.

These turtles do not nest in Europe or Canada. They come only to feed, building up fat reserves before swimming back to tropical beaches in the Caribbean, French Guiana or West Africa. On the Pacific side, waters off central California hold a seasonal feeding area for turtles that nest in Indonesia. The United States designated about 108,000 square km (41,900 square mi) of Pacific coastal waters off California, Oregon and Washington as critical habitat for leatherbacks in 2012.

Myths and facts

Myth: leatherbacks are warm-blooded. They are reptiles and do not produce body heat the way mammals and birds do at rest. Their warmth comes from constant swimming, large size and good insulation, which is enough to keep their core far warmer than cold seawater.

Myth: all sea turtles return to the exact beach where they hatched. Most sea turtles show strong loyalty to their home region, but leatherbacks are less precise than other species. Females often switch between beaches within a region, possibly because the soft, open beaches they prefer shift and erode from year to year.

Fact: leatherbacks really can cross oceans. Satellite tracking has followed individuals for thousands of kilometers, including full crossings of the Pacific and the Atlantic.

Reproduction and life cycle

Mating takes place at sea. Males never come ashore after they hatch. Females return to land every two to three years to nest, usually on sandy beaches facing deep water, such as those of Gabon, French Guiana, Suriname, Trinidad, Costa Rica and Papua. Smaller numbers nest in Florida, Puerto Rico and the US Virgin Islands.

A nesting female crawls up the beach at night, digs a flask-shaped hole with her rear flippers and lays about 80 to 100 fertile eggs the size of billiard balls, often with a layer of smaller yolkless eggs on top. She nests several times in one season, typically around five to seven times at intervals of about 9 to 10 days. The eggs hatch after about 60 to 65 days, and as in other sea turtles, warmer nests produce more females.

Little is known about how long leatherbacks live or when they mature. Estimates of the age at first breeding range from under 10 years to around 30 years depending on the study and population, and the natural lifespan is thought to be several decades.

Predators and threats

Eggs and hatchlings face many predators, including crabs, raccoons, dogs, birds and fish. Adults have few natural enemies, though killer whales, large sharks, jaguars on some beaches and saltwater crocodiles occasionally kill them.

The serious threats come from people. Leatherbacks drown after being caught in longlines, gillnets and trap ropes as bycatch. Egg collection devastated nesting populations in Southeast Asia: in Terengganu, Malaysia, thousands of females once nested each year, but the population has effectively disappeared. Other threats include boat strikes, plastic pollution, coastal development and artificial lights that lead hatchlings away from the sea, and rising sand temperatures linked to climate change. Read more in why are sea turtles endangered.

Conservation status

The IUCN Red List classes the leatherback as Vulnerable worldwide, with a decreasing population trend. Some subpopulations are in far worse shape. The eastern Pacific and western Pacific populations are listed as Critically Endangered, and the northwest Atlantic population as Endangered. The number of females nesting worldwide each year is estimated in the tens of thousands, far fewer than a few decades ago.

The species is protected under CITES Appendix I and listed as endangered under the US Endangered Species Act. Conservation work includes beach patrols and protected nesting reserves, such as Las Baulas National Marine Park in Costa Rica, rules to reduce bycatch in fisheries, and limits on beach lighting. Atlantic populations have generally fared better than those in the Pacific, showing that protection on the beaches and at sea can make a difference.

Leatherbacks and people

Leatherback meat is oily and rarely eaten, but eggs are still collected in some places. Several cultures hold the turtle in special regard: the Seri people of Sonora, Mexico, consider it one of their creators. Leatherbacks also help people indirectly by eating jellyfish, which compete with and prey on young fish. Like the hawksbill sea turtle on coral reefs, the leatherback plays a role in its ecosystem that no other animal fills.