Leatherback seaturtles

(Dermochelyidae)

Class Reptilia

Order Testudines

Suborder Cryptodira

Family Dermochelyidae

Thumbnail description
A huge marine turtle with a smooth, leathery, black, teardrop-shaped carapace, with scattered small white or yellow blotches

Size
Up to 96 in (244 cm) and 1,911 lb (867 kg)

Number of genera, species
1 genus; 1 species

Habitat
Oceans

Conservation status
Critically Endangered

Distribution
Worldwide, oceanic

Evolution and systematics

The leatherback seaturtle (Dermochelys coriacea) is most closely related to the other marine turtles of the family Cheloniidae. The family Dermochelyidae is known from the Eocene to the Pliocene in Africa, Europe, Japan, Antarctica, Peru, and North America. The Pacific and Atlantic populations differ genetically and have been recognized as separate subspecies by some authors. This seaturtle is also commonly known as caldon (Trinidad), canal (Caribbean, Latin America), caouana (Carib Indians), cardon (Venezuela), laúd, luth, and trunk turtle. No subfamilies are recognized.

The taxonomy of this species is Testudo coriacea Vandelli, 1761, Mediterranean and Adriatic seas.

Physical characteristics

The smooth, streamlined carapace is teardrop shaped (up to 96 in [244 cm] in length), bears seven longitudinal ridges, lacks epidermal scutes, and is covered with leathery skin. Most of the bones of the carapace have been lost, but a mosaic of hundreds of small dermal bones lies just under the leathery skin. The head also lacks scales and has a prominent toothlike cusp on each side of the upper jaw. The shell and skin are generally black with scattered white or yellow blotches or spots. The plastron is predominately white with scattered dark blotches or spots. The forelimbs are paddle-like and lack claws.

Distribution

This pelagic species has perhaps the greatest distribution of any reptile. It is found in all tropical oceans (and in the Mediterranean Sea), and it also ventures into the cold temperate waters around Newfoundland, Iceland, Norway, the Cape of Good Hope, New Zealand, and Alaska. Its nesting is on tropical and subtropical shores.

Habitat

This species is pelagic, and is only rarely found in shallow bodies of water.

Behavior

Leatherback seaturtles make extensive migrations between feeding and nesting areas. Recaptures have been made more than 3,100 mi (5,000 km) away, and individuals have traveled an average of more than 19 mi (30 km) per day for weeks at a time. Feeding takes place in both cold and warm water environments, in large part because leatherbacks can maintain body temperatures above environmental temperatures. Body heat generated by muscle activity is lost very slowly due to the thermal inertia of the large body, excellent insulative properties of the oily skin, and countercurrent circulatory system in the limbs which keeps the heat in the body's core. Leatherbacks sometimes aggregate, probably in association with feeding (e.g., on schools of jellyfish). They also are capable of making dives to depths of more than 3,300 ft (1,000 m) to reach food sources. They are active both day and night, although diving activity is increased at night. As they leave the nest, hatchlings are attracted to open, highly illuminated areas (usually the open sea).

Feeding ecology and diet

Leatherbacks are almost completely carnivorous, preferring oceanic jellyfish. However, they also consume hydrozoans,

snails, bivalves, octopi, squid, amphipod crustaceans, crabs, sea urchins, tunicates, and small fish, as well as algae, kelp, and sea grasses. Unfortunately, plastic bags or balloons dumped in the ocean by humans are often mistaken for jellyfish and, if consumed, can block the gastrointestinal tract, causing the turtle's death.

Reproductive biology

Based on growth rings formed annually in the long bones of leatherbacks, sexual maturity is reached at about 13 to 14 years. Courtship and mating have only rarely been observed, and are known to occur in tropical water (e.g., near nesting beaches), but may also occur before or during migration to the nesting beaches. Nesting occurs on a great number of tropical beaches, but the number of females using a given beach is often small, and the numbers at even the best sites are declining. Atlantic leatherbacks nest from April to November; those from the Pacific nest at various times of the year depending on the location. Nesting is usually at night, and takes place just above the high tide line, on open sandy beaches free of rocks, etc., that would abrade the soft plastron. The female digs a huge body pit with both forelimbs and hind limbs, and then excavates the actual nest cavity with her hind feet. Once the eggs are laid, the opening to the nest cavity is covered with sand by the hind limbs, and eventually the forelimbs are also used to fill the body pit.

Eggs are spherical, with pliable shells, and are 1.9–2.6 in (49–65 mm) in diameter and weigh 2.5–3.2 oz (70–90 g); however, from one to 103 undersized (0.6–1.8 in [15–45 mm]) and yolkless eggs may be produced along with the normal egg complement, which numbers from 46 to 160. Clutch and egg size both tend to increase with female size. Clutch sizes are also generally larger on Atlantic beaches than on eastern Pacific beaches, and clutches laid during the middle of the nesting season are usually larger than those in early or late nests. Females oviposit up to 11 times during a nesting season, although half that many clutches per season is more usual. Females nest only every two or three years. Incubation requires 50–78 days, but most undisturbed nests apparently hatch in 60–68 days. Most hatchlings leave the nest at night. Sex is determined by temperature during the middle third of incubation, with only females produced at high temperatures and only males at low ones.

Conservation status

This species is listed as Critically Endangered on the IUCN Red List, as Endangered by the U.S. Fish and Wildlife Service, and in Appendix I of the CITES.

Significance to humans

Population estimates suggest that this species has declined by more than 70% in less than one generation. Egg poaching has been the primary reason for the decline in this species, although adults are also harvested in many areas for their flesh and/or the oil in their shells.

Resources

Books

Pritchard, Peter C. H., and Pedro Trebbau. The Turtles of Venezuela. Athens, OH: Society for the Study of Amphibians and Reptiles; Oxford, OH, 1984.

Periodicals

Spotila, James R., et al. "Worldwide Population Decline of Dermochelys coriacea: Are Leatherback Turtles Going Extinct?" Chelonian Conservation and Biology 2, no. 2 (1996): 209–222.

Steyermark, Anthony C., et al. "Nesting Leatherback Turtles at Las Baulas National Park, Costa Rica." Chelonian Conservation and Biology 2, no. 2 (1996): 173–183.

Tucker, A. D., and N. B. Frazer. "Reproductive Variation in Leatherback Turtles, Dermochelys coriacea, at Culebra National Wildlife Refuge, Puerto Rico." Herpetologica 47 (1991): 115–124.

Wood, Roger C., Jonnie Johnson-Gove, Eugene S. Gaffney, and Kevin F. Maley. "Evolution and Phylogeny of the Leatherback Turtles (Dermochelyidae), with Descriptions of New Fossil Taxa." Chelonian Conservation and Biology 2, no. 2 (1996): 266–286.

Zug, George R., and James F. Parham. "Age and Growth in Leatherback Turtles, Dermochelys coriacea (Testudines: Dermochelyidae): A Skeletochronological Analysis." Chelonian Conservation and Biology 2, no. 2 (1996): 244–249.

John B. Iverson, PhD