Animal Spotlight: Leatherback Sea Turtle

Taxonomy:leatherback

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Reptilia
  • Order: Testudines
  • Family: Dermochelyidae
  • Genus: Dermochelys
  • Species: Coriacea

 

  • Average Size: 7 ft (2 m)
  • Average Weight: 660 to 1,100 lbs (300 to 500 kg)
  • *Heaviest recorded weight was 2,00 lbs or 900 kg
  • Length of Front Flippers: 8.9 ft (2.7 m)
  • Maturity At: 15 to 20 years
  • Estimated Average Age: 45 years

Leatherbacks have the widest global distribution of all reptile species. Primarily located in the open ocean, they can be found in the tropic and temperate waters of the Atlantic, Pacific, Indian Oceans, and Mediterranean Sea but will also travel as far north as Canada and Norway and as far south as New Zealand and South America. They are the largest of all living sea turtles and the fourth largest modern reptile behind three crocodilians.

Leatherback sea turtles face many predators in their early lives. Eggs dug out of the nest and baby turtles trying to get to the ocean can be eaten by a variety of coastal predators, including ghost crabs, monitor lizards,raccoons, coatis, dogs, coyotes, genets, mongooses, and shorebirds ranging from small plovers to large gulls. Once in the water, the young turtles face predation from cephalopods, requiem sharks, and large fish. Despite the difficulties of growing to adulthood, the huge adults face fewer serious predators. They may occasionally be overwhelmed and preyed on by large marine predators like killer whales, great white sharks, and tiger sharks. Nesting females have also been preyed by jaguars in the American tropics. Leatherbacks are threatened by human activities that interfere with the turtles’ feeding and nesting as well as being injured or killed from boat accidents.

Diet

b9f52dc71702e14e99bb85cfa0b790c5Due to their delicate, scissor-like jaws, if the turtles eat anything other than soft-bodied organisms, it would cause jaw damage. Their main staple food is jellyfish but will also feed on salps, pyrosomes, sea urchins, squid, crustaceans, tunicates, fish, blue-green algae, and floating seaweed.

The Leatherback can consume about 73% of its own body weight of jellyfish in a single day, amounting to about 16,000 calories, three to seven times more than it needs to survive.

Anatomy

Leatherbacks have the most hydrodynamic body design of any sea turtle with its large, teardrop-shaped body. Its large flattened front flippers are adapted for swimming in the open ocean. Claws are absent from both pairs of flippers.

Leatherback sea turtles are also the only sea turtle species that lacks a hard shell. Instead of scutes, the thickened horny or bony plates that make up the shells of turtles and crocodiles, they have thick, leathery skins embedded with minuscule osteoderms, bony deposits in the dermal layer of the skin. Seven distinct ridges rise from the shell, or carapace, from the anterior to posterior margin of the turtle’s back. Their shells are normally dark grey to black with white or pale spots, while the underbellies are pinkish-white.

Unlike other reptiles, Leatherback sea turtles are able to maintain warm body temperatures and are able to survive in water that is too cold for other marine turtles. Their unique set of adaptations have allowed these sea creatures to retain and even generate body heat.

These adaptations include their large body size, changes in blood flow, and a thick layer of fat.  Their high volume to surface area ratio means that the turtle has a relatively small surface area compared to its significant body mass, allowing the turtle to retain body heat. Leatherbacks also have a “countercurrent” heat exchangers in their flippers with their veins and arteries closely bundled next to one another. This way, the warmer blood carried away from the heart in the arteries helps to warm the cooler blood returning to the heart from the veins. Furthemore, underneath the leathery skin of the belly is a thick layer of fat like marine mammals. In most sea turtles, the lower shell is made up of nine bones that are fused together to create a solid plate. But in the Leatherback, these bones are reduced to a ring around the edge and is filled with the layer of fat. Any heat generated by muscle movement is contained by this fatty layer. These factors help the the Leatherback maintain a body temperature to almost 18 Celsius warmer than the surrounding water temperature.

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Leatherback sea turtles, like other turtles, lack teeth. They only have two cusps, pointed parts, on their upper jaw and one on their lower jaw to grab their food. Instead, they have backward spines down its mouth and esophagus to help swallow the soft-bodied prey, like jellyfish. The sharp papillae actually prevent the jelly from escaping by floating back out of the mouth, allowing for the Leatherback to feed on a variety of jellyfish species. In addition to the papillae, the turtle also have an unusually long esophagus that extends past its stomach to the rear. From there, it loops back up to connect with the stomach. A long esophagus allows for the Leatherback to swallow large amounts of jellyfish at a time.

Behavior

The Leatherback sea turtle is a migratory species, travelling over 10,000 miles a year between breeding and feeding areas, averaging 3,700 miles (6,000 kilometers) each way. The migration occurs between the cold waters where leatherbacks feed to the tropical and subtropical beaches in the regions where they hatch.

It needs all the energy it can get to cover large distances, but jellyfish aren’t exactly energy-boosting foods with their high water content. This accounts for the Leatherback’s huge appetite and long esophagus.

Leatherbacks follow their jellyfish prey throughout the day, resulting in turtles preferring deeper water in the daytime and shallower water at night, when the jellyfish rise up the water column. This often places turtles in very frigid waters where their ability to retain and even possibly generate body heat despite being reptiles comes in handy. They are also known to pursue their prey deeper than 1,000 meters which is beyond the physiological limits of all other diving tetrapods except for beaked whales and sperm whales.

Female Leatherbacks migrate to their respective nesting sites and come ashore during the breeding seasons every two or three years. Their ritual involves excavating a hole in the sand, laying an average of four to seven clutches of approximately 100 eggs during a nesting season. Once the eggs are laid, leatherback sea turtles, like other reptiles, leave the hatchlings to fend for themselves. Only about 1 out of 4 will survive its first day and about 1 out of 10,000 survives to reproduce again.1

The temperature inside the nest determines the sex of the hatchlings. A mix of male and
female hatchlings occurs when the nest temperature is approximately 85.1 degrees Fahrenheit (29.5 degrees Celsius) but higher temperatures produce a higher ratio of females and cooler temperatures produce a higher ratio of males.

After the eggs are incubated for about 55 to 75 days, the Leatherback hatchlings emerge from the nest and quickly scramble to get to the ocean water.

Subpopulations

The global population of Leatherbacks comprises of seven biologically and geographically subpopulations located in the Pacific, Atlantic, and Indian Ocean.

The East Pacific subpopulation is considered critically endangered with a decreasing population trend. It is estimated to have only 633 mature individuals. They nest along the Pacific coast of Mexico, Central, and South America with its area of occupancy of 2,000 km2 extending from Baja California, Mexico, to central Chile, and westward to 130°W and south to 40°S. This subpopulation has declined 97.4% during the past three generations. IUCN’s long-term abundance trends analysis from long-term monitoring projects on primary nesting beaches in Mexico and Costa Rica demonstrates that nesting abundance has declined more than 90% since the 1980s. It is estimated to be nearly extinct with a population decline of 99.9% in another generation (i.e. by 2040), with a remaining abundance of approximately 52 nests per year or fewer than 30 adults female total.

The West Pacific subpopulation is also considered critically endangered with a decreasing population trend. It is estimated to have only 1,438 mature individuals. Due to the beach temperatures, this subpopulation has a 3:1 female to male ratio. Their region extends north into the Sea of Japan, northeast and east into the North Pacific to the west coast of North America, west to South China Sea and Indonesian Seas, and south into the high latitude waters of the western South Pacific Ocean and Tasman Sea. They nest primarily in Papua Barat, Indonesia, Papua New Guinea, and the Solomon Islands as well as in Vanuatu. Their largest nesting population in Terrengannu, Malaysia, is now functionally extinct. IUCN’s long-term abundance trends analysis in the western Pacific demonstrates that nesting abundance has declined at the two Indonesian index beaches by 78.3% over 27 years at Jamursba-Medi and by 62.8% over the past nine years at Wermon. The West Pacific Leatherback subpopulation has declined 83% during the past three generations. It is estimated that it will continue to diminish with a population decline of 96% in another generation (i.e. by 2040), with a remaining abundance of approximately 572 nests or 260 adult females total.

The Northwest Atlantic subpopulation is considered to be ‘of least concern’ with an increasing population trend. It is estimated to have 29,637 to 33,810 mature individuals. Their range extends throughout the North Atlantic Ocean, from the equator to beyond 50°N, and from the Gulf of Mexico into the Mediterranean and across the equator to northwestern Africa. They nest in southeastern United States, throughout the mainland and insular Caribbean, and the Guiana Shield. Compared to the other subpopulations, the Northwest Atlantic subpopulation is large. There has been an increase of 20.6% with over 50,000 nests over the past three generations and is projected to increase to over 180,000 nests in the next generation (by 2040). Despite being listed as ‘of least concern’, the future population increases depend on the success of current conservation efforts to protect the subpopulation and its habitat.

The Southwest Atlantic subpopulation is considered as critically endangered, but they do have an increasing population trend. It is estimated to have only 35 mature individuals with an estimated area of occupancy of 320 km2. Their range is thought to extend north across the equator in Brazil and east to the coast of Atlantic Africa, southwest to southern Brazil, Uruguay, and Argentina, and southeast to South African waters. Despite its large range, they nest only in Brazil. The Southwest Atlantic subpopulation has increased by 232% over the past three generations and estimated to increase by 957% in another generation (i.e. by 2040) with an abundance of approximately 169 nests or 85 adult females total.

leatherback-01

The Southeast Atlantic subpopulation is considered as data deficit with an unknown population trend. Although the they share identical geographical distribution with the Southwest Atlantic subpopulation, they are genetically distinct and do not breed together. The nesting epicenter lies in Bioko Island, Equatorial Guinea, Gabon, and Republic of Congo, with additional nesting in smaller numbers extending north to Senegal and south to Angola. Trend data is unavailable for the nesting site in Gabon. Although data is available for the nesting sites in Congo and Equatorial Guinea, they make up a cumulative abundance of less than 10% of the abundance in Gabon, the largest Leatherback nesting population in the world. This does not make it ideal to assign the trends observed in Congo and Equatorial Guinea to the entire subpopulation.

The Northwest Indian subpopulation is considered critically endangered with a decreasing population trend. It is estimated to have only 148 mature individuals occupying an area of 1,500 km2. Their range extends through the Agulhas Current around the Cape of Good Hope in the Indian and Atlantic Oceans but they nest along the Indian Ocean coast of South Africa and Mozambique. This subpopulation has a similar sex ratio as East Pacific’s. The Northwest Indian subpopulation has declined slightly by 5.6% during the past three generations. The reason for its status as critically endangered is due to its restricted range of a single location and small population size.

The Northeast Indian subpopulation is considered as data deficit with an unknown population trend. Their range includes Bangladesh, India, Indonesia, Malaysia, Myanmar, Sri Lanka, and Thailand. They nest primarily in the Andaman and Nicobar Islands, Sri Lanka, and to a less extent in Thailand and Sumatra, India. The nesting population in Sri Lanka is estimated to be 100 to 200 females per year, in the Andaman and Nicobar Islands, approximately 400 to 600 females per year, and in Thailand, there are fewer than 10 nests. There is a significant gap in the knowledge and understanding of the Northeast Indian subpopulation. It is hypothesized that the nesting beaches in Sri Lanka and the Nicobar Islands might belong to a third distinct Indian Ocean subpopulation.

Conservation/Threats

Once prevalent in every ocean except the Arctic and Antarctic, the leatherback population is rapidly declining in many parts of the world. Estimation of global population change based on subpopulation trends, weighted based on relative size to the global population size, produced an estimate of 40.1% decline over the past three generations.

Currently listed as ‘vulnerable’ on IUCN, the global Leatherback sea turtle’s projected population based off of the subpopulation trends show that by 2030, population will be increasing by 3%. Therefore, within the next ten years, the global population might no longer be qualified to be listed as vulnerable. However, a future population increase is dependent on the success of conservation actions to mitigate current and future threats through its range.

leatherback1Nearly 99% of the global population is contained with the Northwest Atlantic subpopulation, which obscures the declines and threatened status of the Pacific and Indian subpopulations. So while the results demonstrate that the species will not extinct globally, subpopulations are still at risk and should be given priority.

There are five main threats to this species’ survival. Fisheries bycatch, the incidental capture of marine turtles in fishing gear targeting other species, is listed as the greatest threat to Leatherbacks globally. Many Leatherbacks fall victim to fishing lines and nets, or are even struck by boats. Turtles and eggs directly taken for human consumption and coastal development affecting turtle habitat and nesting sites are the next greatest threats. Pollution, debris, and pathogens caused by humans affects marine turtles and their health. Leatherback sea turtles, in particular, die from ingesting plastic bags that look similar to jellyfish in the water. Some individuals have been found to have almost 11 pounds or 5 kilograms of plastic in their stomachs The current and future impacts from climate change will affect marine turtles in their habitats in ways such as increasing sand temperatures, sea level rise, and storm frequency.

Interesting Facts

  • Leatherbacks untake the longest migrations of any sea turtle species.
  • The largest Leatherback found was an 8.5 ft (2.6 m) long male weighing 2,020 lbs (916 kg) that washed up on the west coast of Wales in 1988.
  • They have never been successfully raised to maturity in captivity.
  • They cannot swim backwards.
  • They can dive to depths of 4,200 feet (1,280 meters) and can stay down for up to 85 minutes.
  • They are the fastest-moving reptiles. The 1992 edition of the Guinness Book of World Records lists the leatherback turtle moving at 21.92 mph (35.28 km/h) in the water. Typically, Leatherback sea turtles swim at 1.12-6.26 mph (1.8-10.08 km/h).

Warning: This video contains dissections.

References + For More Reading

NatGeo: Leatherback Sea Turtle

US FWS: Leatherback Sea Turtle

Fisheries and Oceans Canada: Leatherback Sea Turtle

Network for Endangered Sea Turtles: Leatherback Sea Turtles

Believe It or Not the Scariest Mouth in the World Belongs to a Species of Turtle

The Anatomy of Sea Turtles

IUCN: Dermochelys coriacea

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