The Leatherback Sea Turtle (Dermochelys coriacea) is the largest of all living sea turtles and the fourth largest modern reptile behind three crocodilians. It can easily be differentiated from other modern sea turtles by its lack of a bony shell. Instead, its carapace is covered by skin and oily flesh. This species is the most often encountered in British waters of all sea turtles.
Anatomy and physiologyEdit
Leatherback turtles have the most hydrodynamic body design of any sea turtle, with a large, teardrop shaped body. A large pair of front flippers power the turtles through the water. Like other sea turtles, the leatherback's flattened forelimbs are 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 meters (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 anterior to posterior 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.
Dermochelys coriacea adults average 1–2 metres (3.3–6.6 ft) long and weigh 250 to 700 kilograms (550 to 1,500 lb).The largest ever found however was over 3 meters (10 ft) from head to tail and weighed 916 kilograms (2,019 lb). That specimen was found on a beach on the west coast of Wales.
Dermochelys coriacea exhibits a suite of anatomical characteristics that are believed to be associated with a life in cold waters, including an extensive covering of brown adipose tissue, temperature independent swimming muscles, counter-current heat exchangers between the large front flippers, and the core body, as well as an extensive network of counter-current heat exchangers surrounding the trachea.
Leatherbacks have been viewed as unique among reptiles for their ability to maintain high body temperatures using metabolically generated heat, or endothermy. Initial studies on leatherback metabolic rates found that leatherbacks had resting metabolisms that were around three times higher than expected for a reptile of their size. However, recent studies using reptile representatives encompassing all the size ranges leatherbacks pass through during ontogeny discovered that the resting metabolic rate of a large Dermochelys coriacea is not significantly different from predicted results based on allometry.
Rather than use a high resting metabolism, leatherbacks appear to take advantages of a high activity rate. Studies on wild D.coriacea discovered that individuals may spend as little as .1% of the day resting. This constant swimming creates muscle derived heat. Coupled with their counter-current heat exchangers, insulative fat covering and large size, leatherbacks are able to maintain high temperature differentials compared to the surrounding water. Adult leatherbacks have been found with core body temperatures that were 18 °C (32.4 °F) above the water they were swimming in.
Leatherback turtles are one of the deepest diving marine animals. Individuals have been recorded diving to depths as great as 1,280 meters (4,199 ft).
They are also the fastest-moving reptiles. The 1992 edition of the Guinness Book of World Records lists the leatherback turtle moving at 35.28 kilometres per hour (21.92 mph) in the water.
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 the Cape of Good Hope 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. Recent estimates of global nesting populations are that 26,000 to 43,000 females nest annually, which is a dramatic decline from the 115,000 estimated in 1980.These declining numbers have energized efforts to rebuild the species, which currently is critically endangered.
Leatherback turtles can be found primarily in the open ocean. Scientists tracked a leatherback turtle that swam from Indonesia to the U.S. in an epic 20,000 kilometers (12,427 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 more shallow 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 (32.7 °F).
Its favored breeding beaches are mainland sites facing deep water and they seem to avoid those sites protected by coral reefs.
Adult Dermochelys coriacea subsist almost entirely on jellyfish. Due to its obligate feeding nature, it has been hypothesized that leatherback turtles help control jellyfish populations. Leatherbacks also feed on other soft-bodied organisms such as tunicates and cephalopods.