Leatherback Sea Turtle

The leatherback sea turtle (Dermochelys coriacea), sometimes called the lute turtle or leathery turtle, is the largest of all living turtles and is the fourth-heaviest modern reptile behind three crocodilians. It is the only living species in the genus Dermochelys and family Dermochelyidae. It can easily be differentiated from other modern sea turtles by its lack of a bony shell, hence the name. Instead, its carapace is covered by skin and oily flesh. Dermochelysis the only extant genus of the family Dermochelyidae.

Anatomy and Physiology[]

Leatherback turtles have the most hydrodynamic body design of any sea turtle, with a large, teardrop-shaped body. A large pair of front flippers powers the turtles through the water. Like other sea turtles, the leatherback has flattened fore limbs adapted for swimming in the open ocean. Claws are absent from both pairs of flippers. The leatherback's flippers are the largest in proportion to its body among extant sea turtles. Leatherback's front flippers can grow up to 2.7 m (8.9 ft) in large specimens, the largest flippers (even in comparison to its body) of any sea turtle.

The leatherback has several characteristics that distinguish it from other sea turtles. Its most notable feature is the lack of a bony carapace. Instead of scutes, it has thick, leathery skin with embedded minuscule osteoderms. Seven distinct ridges rise from the carapace, crossing from the cranial to caudal margin of the turtle's back. Leatherbacks are unique among reptiles in that their scales lack β-keratin. The entire turtle's dorsal surface is colored dark grey to black, with a scattering of white blotches and spots. Demonstrating countershading, the turtle's underside is lightly colored. Instead of teeth, the leatherback turtle has points on the tomium of its upper lip, with backwards spines in its throat to help it swallow food and to stop its prey from escaping once caught.

D. coriacea adults average 1–1.75 m (3.3–5.7 ft) in curved carapace length (CCL), 1.83–2.2 m (6.0–7.2 ft) in total length, and 250 to 700 kg (550 to 1,540 lb) in weight. In the Caribbean, the mean size of adults was reported at 384 kg (847 lb) in weight and 1.55 m (5.1 ft) in CCL. Similarly, those nesting in French Guiana, weighed an average of 339.3 kg (748 lb) and measured 1.54 m (5.1 ft) in CCL. The largest verified specimen ever found was discovered in the Pakistani beach of Sanspit and measured 213 cm (6.99 ft) in CCL and 650 kg (1,433 lb) in weight, a previous contender, the "Harlech turtle", was purportedly 256.5 cm (8.42 ft) in CCL and 916 kg (2,019 lb) in weight however recent inspection of its remains housed at the National Museum Cardiff have found that its true CCL is around 1.5 m (4.9 ft), casting doubt on the accuracy of the claimed weight, as well. On the other hand, a scientific paper claimed that the species can weigh up to 1,000 kg (2,200 lb) without providing more verifiable detail. The leatherback turtle is scarcely larger than any other sea turtle upon hatching, as they average 61.3 mm (2.41 in) in carapace length and weigh around 46 g (1.6 oz) when freshly hatched.

D. coriacea exhibits several anatomical characteristics believed to be associated with a life in cold waters, including an extensive covering of brown adipose tissue, temperature-independent swimming muscles, countercurrent heat exchangers between the large front flippers and the core body, and an extensive network of countercurrent heat exchangers surrounding the trachea.

Distribution[]

The leatherback turtle is a species with a cosmopolitan global range. Of all the extant sea turtle species, D. coriacea has the widest distribution, reaching as far north as Alaska and Norway and as far south as Cape Agulhas in Africa and the southernmost tip of New Zealand. The leatherback is found in all tropical and subtropical oceans, and its range extends well into the Arctic Circle. The three major, genetically distinct populations occur in the Atlantic, eastern Pacific, and western Pacific Oceans. While nesting beaches have been identified in the region, leatherback populations in the Indian Ocean remain generally unassessed and unevaluated.

Ecology and Life History[]

Habitat[]

Leatherback turtles can be found primarily in the open ocean. Scientists tracked a leatherback turtle that swam from Jen Womom beach of Tambrauw regency in West Papua province of Indonesia to the U.S. in a 20,000 km (12,000 mi) foraging journey over a period of 647 days. 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 hunting strategy often places turtles in very frigid waters. One individual was found actively hunting in waters that had a surface temperature of 0.4 °C. (32.72 °F). Leatherback turtles are known to pursue prey deeper than 1000 m — beyond the physiological limits of all other diving tetrapods except for beaked whales and sperm whales. Their favored breeding beaches are mainland sites facing deep water, and they seem to avoid those sites protected by coral reefs.

Feeding[]

Adult D. coriacea turtles subsist almost entirely on jellyfish. Due to their obligate feeding nature, leatherbacks help control jellyfish populations. Leatherbacks also feed on other soft-bodied organisms, such as tunicates and cephalopods.

Pacific leatherbacks migrate about 6,000 mi (9,700 km) across the Pacific from their nesting sites in Indonesia to eat California jellyfish. One cause for their endangered state is plastic bags floating in the ocean. Pacific leatherback sea turtles mistake these plastic bags for jellyfish; an estimated one-third of adults have ingested plastic.^[54] Plastic enters the oceans along the west coast of urban areas, where leatherbacks forage, with Californians using upward of 19 billion plastic bags every year.

Several species of sea turtles commonly ingest plastic marine debris, and even small quantities of debris can kill sea turtles by obstructing their digestive tracts. Nutrient dilution, which occurs when plastics displace food in the gut, affects the nutrient gain and consequently the growth of sea turtles. Ingestion of marine debris and slowed nutrient gain leads to increased time for sexual maturation that may affect future reproductive behaviors. These turtles have the highest risk of encountering and ingesting plastic bags offshore of San Francisco Bay, the Columbia River mouth, and Puget Sound.

Lifespan[]

Very little is known of the species' lifespan. Some reports claim "30 years or more", while others state "50 years or more". Upper estimates exceed 100 years.