|Leatherback Sea Turtle|
|Common Name||Lute Turtle|
The Leatherback sea turtle, (Dermochelys coriacea), sometimes called the lute turtle, is the largest known of all living turtles (as well as the largest known extant sea turtle) and is the fourth largest known modern reptile behind three crocodilians. It is the only living species in the genus Dermochelys. 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. The leatherback sea turtle is the only extant member of the family Dermochelyidae.
Taxonomy and evolution
Dermochelys coriacea is the only species in genus Dermochelys. The genus, in turn, contains the only extant member of the family Dermochelyidae. ... The leatherback was then reclassified as Dermochelys coriacea. In 1843, the zoologist Leopold Fitzinger put the genus in its own family, Dermochelyidae.
Anatomy and physiology
- The carapace is dark with white or pink spots. The bones are covered by skin and seven keels that go from the neck to the tail.
- The front flippers of a leatherback sea turtle are bigger than those of the other sea turtle species. They measure around two meters.
- The flippers have a paddle-like shape and do not have claws.
- It does not have teeth but the beak has a W-shape and has hooks and spines inside the mouth and throat that are used to capture its prey.
Leatherbacks have the widest distribution of all sea turtle species. They are found throughout the Pacific, Atlantic, and Indian Oceans. In the Pacific, their range extends as far north as Alaska and south beyond the southernmost tip of New Zealand. In the Atlantic, they can be found as far north as Norway and the Arctic Circle and south to the tip of Africa. They are mainly pelagic (open ocean) wanderers but migrate to tropical and subtropical coastal regions to mate and nest.
Ecology and life history
Leatherback sea 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 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 the deep water, and they seem to avoid those sites protected by coral reefs.
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. 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.
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.
Dead leatherbacks that wash ashore are microecosystems while decomposing. In 1996, a drowned carcass held sarcophagid and calliphorid flies after being picked open by a pair of Coragyps atratus vultures. Infestation by carrion-eating beetles of the families Scarabaeidae, Carabidae, and Tenebrionidae soon followed. After days of decomposition, beetles from the families Histeridae and Staphylinidae and anthomyiid flies invaded the corpse, as well. Organisms from more than a dozen families took part in consuming the carcass.
Leatherback turtles face many predators in their early lives. Eggs may be preyed on by a diversity of coastal predators, including ghost crabs, monitor lizards, raccoons, coatis, dogs, coyotes, genets, mongooses, and shorebirds ranging from small plovers to large gulls. Many of the same predators feed on baby turtles as they try to get to the ocean, as well as frigatebirds and varied raptors. Once in the ocean, young leatherbacks still face predation from cephalopods, requiem sharks, and various large fish. Despite their lack of a hard shell, the huge adults face fewer serious predators, though they are occasionally overwhelmed and preyed on by very large marine predators such as killer whales, great white sharks, and tiger sharks. Nesting females have been preyed upon by jaguars in the American tropics.
The adult leatherback has been observed aggressively defending itself at sea from predators. A medium-sized adult was observed chasing a shark that had attempted to bite it and then turned its aggression and attacked the boat containing the humans observing the prior interaction. Dermochelys juveniles spend more of their time in tropical waters than do adults.
Adults are prone to long-distance migration. Migration occurs between the cold waters where mature leatherbacks feed, to the tropical and subtropical beaches in the regions where they hatch. In the Atlantic, females tagged in French Guiana have been recaptured on the other side of the ocean in Morocco and Spain.
Mating takes place at sea. Males never leave the water once they enter it, unlike females, which nest on land. After encountering a female (which possibly exudes a pheromone to signal her reproductive status), the male uses head movements, nuzzling, biting, or flipper movements to determine her receptiveness. Males can mate every year but the females mate every two to three years. Fertilization is internal, and multiple males usually mate with a single female. This polyandry does not provide the offspring with any special advantages. A leatherback turtle with eggs, photo taken on Salines de Montjoly beach (French Guiana) While other sea turtle species almost always return to their hatching beach, leatherbacks may choose another beach within the region. They choose beaches with soft sand because their softer shells and plastrons are easily damaged by hard rocks. Nesting beaches also have shallower approach angles from the sea. This is a vulnerability for the turtles because such beaches easily erode. They nest at night when the risk of predation and heat stress is lowest. As leatherback turtles spend the vast majority of their lives in the ocean, their eyes are not well adapted to night vision on land. The typical nesting environment includes a dark forested area adjacent to the beach. The contrast between this dark forest and the brighter, moonlit ocean provides directionality for the females. They nest towards the dark and then return to the ocean and the light. Baby leatherback turtle Females excavate a nest above the high-tide line with their flippers. One female may lay as many as nine clutches in one breeding season. About nine days pass between nesting events. Average clutch size is around 110 eggs, 85% of which are viable. After laying, the female carefully back-fills the nest, disguising it from predators with a scattering of sand.
Cleavage of the cell begins within hours of fertilization, but development is suspended during the gastrulation period of movements and infoldings of embryonic cells, while the eggs are being laid. Development then resumes, but embryos remain extremely susceptible to movement-induced mortality until the membranes fully develop after incubating for 20 to 25 days. The structural differentiation of body and organs (organogenesis) soon follows. The eggs hatch in about 60 to 70 days. As with other reptiles, the nest's ambient temperature determines the sex of the hatchings. After nightfall, the hatchings dig to the surface and walk to the sea.
Leatherback nesting seasons vary by location; it occurs from February to July in Parismina, Costa Rica. Farther east in French Guiana, nesting is from March to August. Atlantic leatherbacks nest between February and July from South Carolina in the United States to the United States Virgin Islands in the Caribbean and to Suriname and Guyana.
Leatherback turtles have few natural predators once they mature; they are most vulnerable to predation in their early life stages. Birds, small mammals, and other opportunists dig up the nests of turtles and consume eggs. Shorebirds and crustaceans prey on the hatchings scrambling for the sea. Once they enter the water, they become prey to predatory fish and cephalopods.
Leatherbacks have slightly fewer human-related threats than other sea turtle species. Their flesh contains too much oil and fat to be considered palatable, reducing the demand. However, human activity still endangers leatherback turtles in direct and indirect ways. Directly, a few are caught for their meat by subsistence fisheries. Nests are raided by humans in places such as Southeast Asia. In the state of Florida, there have been 603 leatherback strandings between 1980 and 2014. Almost one-quarter (23.5%) of leatherback strandings are due to vessel-strike injuries, which is the highest cause of strandings. Decaying plastic bag resembling jellyfish Light pollution is a serious threat to sea turtle hatchlings which have a strong attraction to light. Human-generated light from streetlights and buildings causes hatchlings to become disoriented, crawling toward the light and away from the beach. Hatchlings are attracted to light because the lightest area on a natural beach is the horizon over the ocean, the darkest area is the dunes or forest. On Florida's Atlantic coast, some beaches with high turtle nesting density have lost thousands of hatchlings due to artificial light.
Many human activities indirectly harm Dermochelys populations. As a pelagic species, D. coriacea is occasionally caught as bycatch. Entanglement in lobster pot ropes is another hazard the animals face. As the largest living sea turtles, turtle excluder devices can be ineffective with mature adults. In the eastern Pacific alone, a reported average of 1,500 mature females were accidentally caught annually in the 1990s. Pollution, both chemical and physical, can also be fatal. Many turtles die from malabsorption and intestinal blockage following the ingestion of balloons and plastic bags which resemble their jellyfish prey. Chemical pollution also has an adverse effect on Dermochelys. A high level of phthalates has been measured in their eggs' yolks.
- The largest sea turtle species and also one of the most migratory, crossing both the Atlantic and Pacific Oceans.
- These turtles are the most pelagic of all sea turtles, capable of diving to 1300 meters (4,290 feet) to feed primarily on jellyfish, salps, and other gelatinous species.
- Leatherbacks tend to dive for less than 20 minutes per dive, but are capable of diving for up to 37 minutes. •Leatherback nesting occurs from April to November on beaches along the east coast of Florida and the Caribbean, and their lifespan is estimated to be more than 45 years.