Leatherback sea turtle
Conservation status
Critically Endangered (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Order:	Testudines
Suborder:	Cryptodira
Superfamily:	Chelonioidea
Family:	Dermochelyidae
Genus:	Dermochelys Blainville, 1816[2]
Species:	D. coriacea
Binomial name
Dermochelys coriacea (Vandelli, 1761)[1]
Synonyms
Testudo coriacea Vandelli, 1761

The leatherback sea turtle (Dermochelys coriacea), sometimes called the lute turtle, is the largest of all living sea turtles and the fourth largest modern reptile behind three crocodilians.^[3][4] 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. Dermochelys coriacea is the only extant member of the family Dermochelyidae.

Anatomy and physiology[link]

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 metres (8.9 ft) in large specimens, the largest flippers (even in comparison to its body) of any sea turtle.

A leatherback turtle covering her eggs, Turtle Beach, Tobago

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.^[5][6]

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 1–1.75 metres (3.3–5.74 ft) in carapace length, 1.83–2.2 metres (6.0–7.2 ft) in total length and weigh 250 to 700 kilograms (550 to 1,500 lb).^[5][7] The largest ever found, however, was over 3 metres (9.8 ft) from head to tail, including a carapace length of over 2.2 metres (7.2 ft), and weighed 916 kilograms (2,020 lb).^[8] That specimen was found on a beach on the west coast of Wales.^[9]

Dermochelys coriacea exhibits a suite of anatomical characteristics believed to be associated with a life in cold waters, including an extensive covering of brown adipose tissue,^[10] temperature independent swimming muscles,^[11] 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.^[12]

Physiology[link]

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 leatherbacks had resting metabolisms around three times higher than expected for a reptile of their size.^[13] However, recent studies using reptile representatives encompassing all the size ranges leatherbacks pass through during ontogeny discovered the resting metabolic rate of a large Dermochelys coriacea is not significantly different from predicted results based on allometry.^[14]

Rather than use a high resting metabolism, leatherbacks appear to take advantages of a high activity rate. Studies on wild D.coriacea discovered individuals may spend as little as 0.1% of the day resting.^[15] This constant swimming creates muscle-derived heat. Coupled with their counter-current heat exchangers, insulating 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.^[16]

Leatherback turtles are one of the deepest diving marine animals. Individuals have been recorded diving to depths as great as 1,280 metres (4,200 ft).^[17][18] Typical dive durations are between 3 and 8 minutes, with dives of 30–70 minutes occurring infrequently.^[19]

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.^[20][21] More typically, they swim at 0.5–2.8 metres per second (1.1–6.3 mph).^[22]

Distribution[link]

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.^[5] The leatherback is found in all tropical and subtropical oceans, and its range extends well into the Arctic Circle.^[23]

There are three major, genetically distinct populations. The Atlantic Dermochelys population is separate from the ones in the eastern and western Pacific, which are also distinct from each other.^[3][24]

While nesting beaches have been identified in the region, leatherback populations in the Indian Ocean remain generally unassessed and unevaluated.^[25]

D. coriacea distribution - yellow circles represent minor nesting locations, red circles are known major nesting sites.

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.^[26] These declining numbers have energized efforts to rebuild the species, which currently is critically endangered.^[26]

Atlantic subpopulation[link]

The leatherback turtle population in the Atlantic Ocean ranges across the entire region. They range as far north as the North Sea and to the Cape of Good Hope in the south. Unlike other sea turtles, leatherback feeding areas are in colder waters, where there is an abundance of their jellyfish prey, which broadens their range. However, only a few beaches on both sides of the Atlantic provide nesting sites.^[27]

Off the Atlantic coast of Canada, leatherback turtles feed in the Gulf of Saint Lawrence near Quebec and as far north as Newfoundland and Labrador.^[28] The most significant Atlantic nesting sites are in Suriname, French Guiana and Trinidad and Tobago in the Caribbean and Gabon in Central Africa. The beaches of Mayumba National Park in Mayumba, Gabon host the largest nesting population on the African continent and possibly worldwide, with nearly 30,000 turtles visiting its beaches each year in April.^[24][29][29] Off the northeastern coast of the South American continent, a few select beaches between French Guiana and Suriname are primary nesting sites of several species of sea turtles, the majority being leatherbacks.^[30] A few hundred nest annually on the eastern coast of Florida.^[4] In Costa Rica, the beaches of Gandoca and Parismina provide nesting grounds.^[25][31]

Pacific subpopulation[link]

Pacific leatherbacks divide into two populations. One population nests on beaches in Papua, Indonesia and the Solomon Islands and forage across the Pacific in the Northern Hemisphere, along the coasts of California, Oregon, and Washington in North America. The eastern Pacific population forages in the Southern Hemisphere, in waters along the western coast of South America, nesting in Mexico, El Salvador and Costa Rica.^[24][32]

The continental United States offers two major leatherback feeding areas. One well-studied area is just off the northwestern coast near the mouth of the Columbia River. The other American area is located in the state of California.^[32] Further north, off the Pacific coast of Canada, leatherbacks visit the beaches of British Columbia.^[28]

South China Sea subpopulation[link]

A third possible Pacific subpopulation has been proposed, those that nest in Malaysia. This subpopulation, however, has effectively been eradicated. The beach of Rantau Abang in Terengganu, Malaysia, once had the largest nesting population in the world, hosting 10,000 nests per year. The major cause for the decline was egg consumption by humans. Conservation efforts initiated in the 1960s were ineffective because they involved excavating and incubating eggs at artificial sites which inadvertently exposed the eggs to high temperatures. It only became known in the 1980s that sea turtles undergo temperature-dependent sex determination; it is suspected that nearly all the artificially-incubated hatchlings were female.^[33] In 2008, two turtles nested at Rantau Abang, and unfortunately the eggs were infertile.

Indian Ocean subpopulation[link]

While little research has been done on Dermochelys populations in the Indian Ocean, nesting populations are known from Sri Lanka and the Nicobar Islands. These turtles are proposed to form a separate, genetically distinct Indian Ocean subpopulation.^[25]

Ecology and life history[link]

Habitat[link]

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 km (12,000 mi) foraging journey over a period of 647 days.^[5][34] 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).^[15] 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).^[35]

Its favored breeding beaches are mainland sites facing deep water and they seem to avoid those sites protected by coral reefs.^[36]

Feeding[link]

Adult D. coriacea turtles subsist almost entirely on jellyfish.^[5] Due to their obligate feeding nature, leatherback turtles help control jellyfish populations.^[3] Leatherbacks also feed on other soft-bodied organisms, such as tunicates and cephalopods.^[37]

Pacific leatherbacks migrate about 6,000 miles (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 adult leatherbacks have ingested plastic.^[38] Plastic enters the oceans along the west coast of urban areas, where leatherbacks forage; with Californians using upwards of 19 billion plastic bags every year.^[39] 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.^[40] Nutrient dilution, which occurs when plastics displace food in the gut, affects the nutrient gain and consequently the growth of sea turtles.^[41] Ingestion of marine debris and slowed nutrient gain leads to increased time for sexual maturation that may affect future reproductive behaviors.^[42] 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[link]

Very little is known of the species' lifespan. Some reports claim "30 years or more"^[43] while others state "50 years or more" ^[44] .

Death and decomposition[link]

Dead leatherbacks that wash ashore are micro-ecosystems 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.^[45]

Life history[link]

Baby leatherback turtle at Gumbo Limbo Environmental Complex in Boca Raton, Florida

Like all sea turtles, leatherbacks start as hatchlings, climbing out of the sands of their nesting beaches. Birds, crustaceans, various carnivorous mammals, other reptiles, and people prey on hatchlings before they reach the water. Once in the water, several varieties of fish will also readily predate the small hatchlings. About 90% of the hatchlings die from predation. Once in the ocean, they are rarely seen before maturity. Dermochelys juveniles spend more of their time in tropical waters than do adults.^[37] Once they attain maturity few predators threaten the leatherback, although tiger sharks and killer whales are potential predators.^[46]

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.^[30]

Mating takes place at sea. Males never leave the water once they enter it, unlike females which nest on land. After encountering a female (who possibly exudes a pheromone to signal her reproductive status), the male uses head movements, nuzzling, biting, or flipper movements to determine her receptiveness. Females mate every two to three years. However, leatherbacks can breed annually. Fertilization is internal, and multiple males usually mate with a single female. This polyandry does not provide the offspring with any special advantages.^[47]

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.

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.^[5] After laying, the female carefully back-fills the nest, disguising it from predators with a scattering of sand.^[37][48]

	The female back-fills the nest
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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 sixty to seventy 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.^[49][50]

Leatherback nesting seasons vary by location; it occurs from February to July in Parismina, Costa Rica.^[31] Farther east in French Guiana, nesting is from March to August.^[30] 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.^{[citation needed]}

Taxonomy and evolution[link]

Taxonomy[link]

Dermochelys coriacea is the only species in genus Dermochelys. The genus, in turn, contains the only extant member of the family Dermochelyidae.^[51]

Domenico Agostino Vandelli named the species first in 1761 as Testudo coriacea after an animal captured at Ostia and donated to the University of Padua by Pope Clement XIII.^[52] In 1816, French zoologist Henri Blainville coined the term Dermochelys. The leatherback was then reclassified as Dermochelys coriacea.^[53] In 1843, the zoologist Leopold Fitzinger put the genus in its own family, Dermochelyidae.^[54] In 1884, the American naturalist Samuel Garman described the species as Sphargis coriacea schlegelii.^[55] The two were then united in D. coriacea, with each given subspecies status as D. coriacea coriacea and D. coriacea schlegelii. The subspecies were later labeled invalid synonyms of D. coriacea.^[56][57]

The turtle's common name comes from the leathery texture and appearance of its carapace. Older names include "leathery turtle"^[4] and "trunk turtle".^[58]

Evolution[link]

Leatherback turtles have existed in some form since the first true sea turtles evolved over 110 million years ago during the Cretaceous period. The dermochelyids are close relatives of the family Cheloniidae, which contains the other six extant sea turtle species. However, their sister taxon is the extinct family Protostegidae which included other species not having a hard carapace.^[59][60]

Importance to humans[link]

People around the world still harvest sea turtle eggs. Asian exploitation of turtle nests has been cited as the most significant factor for the species' global population decline. In Southeast Asia, egg harvesting in countries such as Thailand and Malaysia has led to a near-total collapse of local nesting populations.^[61] In Malaysia, where the turtle is practically locally extinct, the eggs are considered a delicacy.^[62] In the Caribbean, some cultures consider the eggs to be aphrodisiacs.^[61] They are also a major jellyfish predator^[63][64] which helps keep jellyfish populations in check.

Conservation[link]

Adult 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. Very few survive to adulthood.

Leatherbacks have slightly fewer human-related threats than other sea turtle species. Their flesh contains too much oil and fat, 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.^[61]

Many human activities indirectly harm Dermochelys populations. As a pelagic species, D. coriacea is occasionally caught as bycatch. As the largest living sea turtles, turtle excluder devices can be ineffective with mature adults. A reported average of 1,500 mature females were accidentally caught annually in the 1990s.^[61] 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.^[5] Chemical pollution also has an adverse effect on Dermochelys. A high level of phthalates has been measured in their eggs' yolks.^[61]

Global initiatives[link]

D. coriacea is listed on Appendix I of CITES, which makes export/import of this species (including parts) illegal.

Conserving Pacific and Eastern Atlantic populations was included among the top ten issues in turtle conservation in the first State of the World's Sea Turtles report published in 2006. The report noted significant declines in the Mexican, Costa Rican and Malaysian populations. The eastern Atlantic nesting population was threatened by increased fishing pressures from eastern South American countries.^[65]

The Leatherback Trust was founded specifically to conserve sea turtles, specifically its namesake. The foundation established a sanctuary in Costa Rica, the Parque Marino Las Baulas.^[66]

National and local initiatives[link]

The leatherback sea turtle is subject to differing conservation laws in various countries.

The United States listed it as an endangered species on 2 June 1970. The passing of the Endangered Species Act three years later ratified its status.^[67] In 2012 the National Oceanic and Atmospheric Administration designated 41,914 square miles of Pacific Ocean along California, Oregon and Washington as "critical habitat."^[68] In Canada, the Species At Risk Act made it illegal to exploit the species in Canadian waters. The Committee on the Status of Endangered Wildlife in Canada classified it as endangered.^[28] Ireland and Wales initiated a joint leatherback conservation effort between Swansea University and University College Cork. Funded by the European Regional Development Fund, the Irish Sea Leatherback Turtle Project focuses on research such as tagging and satellite tracking of individuals.^[69]

Earthwatch Institute, a global non-profit that teams volunteers with scientists to conduct important environmental research, launched a program called "Trinidad's Leatherback Sea Turtles." This program strives to help save the world's largest turtle from extinction in Matura Beach, Trinidad, as volunteers work side-by-side with leading scientists and a local conservation group, Nature Seekers. This tropical island off the coast of Venezuela is known for its vibrant ethnic diversity and rich cultural events. It is also the site of one of the most important nesting beaches for endangered leatherback turtles, enormous reptiles that can weigh a ton and dive deeper than many whales. Each year, more than 2,000 female leatherbacks haul themselves onto Matura Beach to lay their eggs. With leatherback populations declining more quickly than any other large animal in modern history, each turtle is precious. On this research project, Dr. Dennis Sammy of Nature Seekers and Dr. Scott Eckert of Wider Caribbean Sea Turtle Conservation Network work alongside a team of volunteers to help prevent extinction of Leatherback Sea Turtles.^[70]

Several Caribbean countries started conservation programs, such as The St. Kitts Sea Turtle Monitoring Network, focused on using ecotourism to highlight the leatherback's plight. On the Atlantic coast of Costa Rica, the village of Parismina has one such initiative. Parismina is an isolated sandbar where a large number of leatherbacks lay eggs, but poachers abound. Since 1998, the village has been assisting turtles with a hatchery program. The Parismina Social Club is a charitable organization backed by American tourists and expatriates, which collects donations to fund beach patrols.^{[71] [72]} Mayumba National Park in Gabon, Central Africa was created to protect Africa's most important nesting beach. More than 30,000 turtles nest on Mayumba's beaches between September and April each year.^[29]

In mid-2007, the Malaysian Fisheries Department revealed a plan to clone leatherback turtles to replenish the country's rapidly declining population. Some conservation biologists, however, are skeptical of the proposed plan because cloning has only succeeded on mammals such as dogs, sheep, cats, and cattle, and uncertainties persist about cloned animals' health and life spans.^[73] Leatherbacks used to nest in the thousands on Malaysian beaches, including those at Terengganu, where more than 3,000 females nested in the late 1960s.^[74] The last official count of nesting leatherback females on that beach was recorded to be a mere two females in 1993.^[24]

In Brazil, reproduction of the leatherback turtle is being assisted by the IBAMA's "projeto TAMAR" (TAMAR project), which works to protect nests and prevent accidental kills by fishing boats. The last official count of nesting leatherback females in Brazil yielded only seven females.^[75] In January 2010, one female at Pontal do Paraná laid hundreds of eggs. Since Leatherback sea turtles had been reported to nest only at Espirito Santo's shore, but never in the state of Paraná, this unusual act brought much attention to the area, biologists have been protecting the nests and checking their eggs' temperature, although it might be that none of the eggs are fertile.^{[76][dated info]}

Australia's Environment Protection and Biodiversity Conservation Act 1999, lists D. coriacea as Vulnerable, while Queensland's Nature Conservation Act 1992 lists it as Endangered.

See also[link]

• Sea turtle threats

Bibliography[link]

Footnotes[link]

References[link]

External links[link]

Wikimedia Commons has media related to: Dermochelys coriacea

• The Reptipage: Leatherbacks break all the rules Detailed literature review of current leatherback knowledge.
• Mayumba National Park Turtles Online Information about and photos of sea turtles and the world's most important leatherback nesting beach.
• ARKive Photographs, Video
• The Oceanic Resource Foundation
• NOAA Office of Protected Resources leatherback turtle page
• Leatherback Sea Turtle at CRESLI
• The Great Turtle Race, a conservation group that monitors Leatherbacks as the swim from Costa Rica, where they've just laid their eggs, back to their natural territory of the Galápagos Islands.
• Tagging Of Pacific Predators, a contributor to The Great Turtle Race, this research group continues to tag and monitor Leatherbacks around the world, including the turtles from the race.
• Video of a leatherback turtle laying eggs Filmed in Tamarindo, Costa Rica
• Ocean Spirits, a Grenadian turtle research NGO.
• Leatherback turtle research at Juno Beach, Florida
• NPWS Leatherback Turtle in Irish waters.
• Baby leatherback turtle hatchlings make their way to the sea on YouTube

v t e Turtle family Dermochelyidae Genus Species of the family Dermochelyidae Dermochelys Leatherback sea turtle Phylogenetic arrangement of turtles based on turtles of the world 2011 update: annotated checklist of taxonomy, synonymy, distribution and conservation status.

v t e Order Testudines (turtles) Kingdom: Animalia Phylum: Chordata Class: Reptilia Subclass: Anapsida Order: Testudines Suborder Superfamily Family Subfamily Genus Cryptodira      Chelydridae   Chelydra Macrochelys Chelonioidea Cheloniidae   Caretta Chelonia Eretmochelys Lepidochelys Natator Dermochelyidae   Dermochelys Kinosternoidea Dermatemydidae   Dermatemys Kinosternidae Kinosterninae Kinosternon Sternotherus Staurotypinae Claudius Staurotypus Testudinoidea Emydidae Deirochelyinae Chrysemys Deirochelys Graptemys Malaclemys Pseudemys Trachemys Emydinae Clemmys Emys Glyptemys Terrapene Geoemydidae   Batagur Cuora Cyclemys Geoclemys Geoemyda Hardella Heosemys Leucocephalon Malayemys Mauremys Melanochelys Morenia Notochelys Orlitia Pangshura Rhinoclemmys Sacalia Siebenrockiella Vijayachelys  Platysternidae   Platysternon Testudinidae   Aldabrachelys Astrochelys Chelonoidis Chersina Cylindraspis Geochelone Gopherus Homopus Indotestudo Kinixys Malacochersus Manouria Psammobates Pyxis Stigmochelys Testudo Trionychia Carettochelyidae   Carettochelys Trionychidae Cyclanorbinae Cyclanorbis Cycloderma Lissemys Trionychinae Amyda Apalone Chitra Dogania Nilssonia Palea Pelochelys Pelodiscus Rafetus Trionyx Pleurodira   Chelidae   Acanthochelys Chelodina Chelus Elseya Elusor Emydura Hydromedusa Mesoclemmys Myuchelys Phrynops Platemys Pseudemydura Rheodytes Rhinemys Pelomedusidae   Pelomedusa Pelusios Podocnemididae   Erymnochelys Peltocephalus Podocnemis Phylogenetic arrangement based on turtles of the world 2011 update: annotated checklist. Extinct turtles not included. See also List of Testudines families Portal

Sea turtles
An olive ridley sea turtle a species of the sea turtle superfamily
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Testudines
Suborder:	Cryptodira
clade:	Polycryptodira
Superfamily:	Chelonioidea Bauer, 1893[1]
Type species
Testudo mydas Linnaeus, 1758
Families
Cheloniidae Dermochelyidae †Protostegidae †Toxochelyidae †Thalassemydidae
Synonyms[1]
Chelonii - Oppel 1811 Chlonopteria - Rafinesque 1814 Cheloniae - Schmid 1819 Edigitata - Haworth 1825 Oiacopodae - Wagler 1828 Pterodactyli - Mayer 1849

Sea turtles (superfamily Chelonioidea) are marine reptiles that inhabit all of the world's oceans except the Arctic.

Distribution[link]

The superfamily Chelonioidea has a world-wide distribution; sea turtles can be found in all oceans except for the polar regions.^{[citation needed]} Some species travel between oceans. The flatback sea turtle is found solely on the northern coast of Australia.

Biology[link]

Respiration[link]

A green sea turtle breaks the surface to breathe.

Sea turtles are almost always submerged, and, therefore, have developed an anaerobic system of energy metabolism. Although all sea turtles breathe air, under dire circumstances they may divert to anaerobic metabolism for long periods of time. When surfacing to breathe, a sea turtle can quickly refill its lungs with a single explosive exhalation and rapid inhalation. Their large lungs have adapted to permit rapid exchange of oxygen and to avoid trapping gases during deep dives.

Life history[link]

According to SeaWorld Parks & Entertainment, a lifespan of 80 years is feasible for sea turtles.^[2] It takes decades for sea turtles to reach sexual maturity. After mating at sea, adult female sea turtles return to land to nest at night. Different species of sea turtles exhibit various levels of philopatry. In the extreme case, females return to the beach where they hatched. This can take place every two to four years in maturity. They make from one to eight nests per season.

A feeding green sea turtle, Chelonia mydas

The mature nesting female hauls herself onto the beach, nearly always at night, and finds suitable sand on which to create a nest. Using her hind flippers, she digs a circular hole 40 to 50 centimetres (16 to 20 in) deep. After the hole is dug, the female then starts filling the nest with a clutch of soft-shelled eggs one by one until she has deposited around 50 to 200 eggs, depending on the species. Some species have been reported to lay 250 eggs, such as the hawksbill. After laying, she re-fills the nest with sand, re-sculpting and smoothing the surface until it is relatively undetectable visually. The whole process takes thirty to sixty minutes. She then returns to the ocean, leaving the eggs untended.^[3]

The hatchling's gender depends on the sand temperature. Lighter sands maintain higher temperatures, which decreases incubation time and results in more female hatchlings.

Hawksbill sea turtle from Black Hills, Honduras

Incubation takes about two months. The eggs in one nest hatch together over a very short period of time. When ready, hatchlings tear their shells apart with their snout and dig through the sand. Again, this usually takes place at night. Once they reach the surface, they instinctively head towards the sea. If, as happens on rare occasions, hatching takes place during daylight, only a very small proportion of each hatch (usually 1%) succeed, because local opportunist predators, such as the common seagull, gorge on the new sea turtles. Thus there is an obvious evolutionary drive to hatch at night, when survival rates on the beach are much higher.

The hatchlings then proceed into the ocean, where a variety of marine predators await them. In 1987, Carr discovered that the young of Chelonia mydas and Caretta caretta spent a great deal of their pelagic lives in floating sargassum beds, where there are thick mats of unanchored seaweed. Within these beds, they found ample shelter and food. In the absence of sargassum beds, sea turtle young feed in the vicinity of upwelling "fronts".^[4] In 2007, Reich determined that green sea turtle hatchlings spend the first three to five years of their lives in pelagic waters. In the open ocean, pre-juveniles of this particular species were found to feed on zooplankton and smaller nekton before they are recruited into inshore seagrass meadows as obligate herbivores.^[5][6]

Instead of nesting individually like the other species, Ridley sea turtles come ashore en masse, known as an "arribada" (arrival). With the Kemp's ridley sea turtles this occurs during the day.

Salt gland[link]

Sea turtles possess a salt excretory gland at the corner of the eye, in the nostrils, or in the tongue, depending on the species; chelonian salt glands are found in the corner of the eyes in leatherback sea turtles. Due to the iso-osmotic makeup of jellyfish and the other gelatinous prey upon which sea turtles subsist, sea turtle diets are high in salt; chelonian salt gland excretions are almost entirely composed of sodium chloride 1500-1800 mosmoll-1 (Marshall and Cooper, 1988; Nicolson and Lutz, 1989; Reina and Cooper, 2000).

Importance to humans[link]

"Manner in which Natives of the East Coast strike turtle". Near Cooktown, Australia. From Phillip Parker King's Survey. 1818.

Marine sea turtles are caught worldwide, although it is illegal to hunt most species in many countries.^[7][8] A great deal of intentional marine sea turtle harvests worldwide are for food.

Many parts of the world have long considered sea turtles to be fine dining. Ancient Chinese texts dating to the fifth century B.C.E. describe sea turtles as exotic delicacies.^[9] Many coastal communities around the world depend on sea turtles as a source of protein, often harvesting several sea turtles at once and keeping them alive on their backs until needed. Coastal peoples gather sea turtle eggs for consumption.^[10]

To a much lesser extent, specific species of marine sea turtles are targeted not for their flesh, but for their shells. Tortoiseshell, a traditional decorative ornamental material used in Japan and China, comes from the carapace scutes of the hawksbill sea turtle.^[11][12] Ancient Greeks and ancient Romans processed sea turtle scutes (primarily from the hawksbill) for various articles and ornaments used by their elites, such as combs and brushes.^[13] The skin of the flippers is prized for use as shoes and assorted leather goods.

The Moche people of ancient Peru worshipped the sea and its animals. They often depicted sea turtles in their art.^[14]

Sea turtles enjoy immunity from the sting of the deadly box jellyfish and regularly eat them, helping keep tropical beaches safe for humans.

Sea turtles, especially green sea turtles, are one of the few animals that eat sea grass. Sea grass needs to be constantly cut short to help it grow across the sea floor. Sea turtles act as grazing animals that cut the grass short and help maintain the health of the sea grass beds. Sea grass beds provide breeding and developmental grounds for numerous species of fish, shellfish and crustaceans. Without sea grass beds, many marine species humans harvest would be lost, as would the lower levels of the food chain. The reactions could result in many more marine species eventually becoming endangered or extinct.^[15]

Beaches and dune systems do not get many nutrients. Sea turtles use beaches and the lower dunes to nest and lay their eggs. Sea turtles lay around 100 eggs in a nest and make between 3 and 7 nests during the summer nesting season. Along a 20-mile stretch of beach on the east coast of Florida sea turtles lay over 150,000 lbs of eggs in the sand. Dune vegetation is able to grow and become stronger with the presence of nutrients from sea turtle eggs, unhatched nests, eggs and trapped hatchlings. As the dune vegetation grows stronger and healthier, the health of the entire beach/dune ecosystem becomes better. Stronger vegetation and root systems help to hold the sand in the dunes and help protect the beach from erosion.^[15]

Beach towns, such as Tortuguero, Costa Rica, have transitioned from a tourism industry that made profits from selling sea turtle meat and shells to an ecotourism-based economy. Tortuguero is considered to be the founding location of sea turtle conservation. In the 1960s the cultural demand for sea turtle meat, shells, and eggs was quickly killing the once abundant sea turtle populations that nested on the beach. The Caribbean Conservation Corporation began working with villagers to promote ecotourism as a permanent substitute to sea turtle hunting. Sea turtle nesting grounds became sustainable. Since the creation of a sea turtle, ecotourism-based economy, Tortugero annually houses thousands of tourists who visit the protected 22-mile beach that hosts sea turtle walks and nesting grounds.^[16][17]

Conservation[link]

A sea turtle entangled in a net

Most species of sea turtle are endangered. Globally, the Kemp's ridley, hawksbill, and leatherback sea turtles are listed as "Critically Endangered", the loggerhead and green as "Endangered", the olive ridley as "Vulnerable" and the flatback as "Data Deficient", meaning that its conservation status is unclear due to lack of data.^[18]. Additionally, all populations of sea turtles that occur in United States waters are listed as threatened or endangered by the United States government, with the leatherback, Kemp's ridley, green, hawksbill, and the Mexican nesting population of the olive ridley all listed as "Endangered", and the loggerhead and non-Mexican populations of olive ridley as "Threatened".^[19] The US listing status of the loggerhead is under review as of 2012.^[20]

One of the most significant threats now comes from bycatch due to imprecise fishing methods. Long-lining has been identified as a major cause of accidental sea turtle death.^[21][22] There is also black-market demand for tortoiseshell for both decoration and supposed health benefits.^[23]

Legal notice posted by nest at Boca Raton, Florida

Sea turtles must surface to breathe. Caught in a fisherman's net, they are unable to surface and thus drown. In early 2007, almost a thousand sea turtles were killed inadvertently in the Bay of Bengal over the course of a few months after netting.^[24]

However, some relatively inexpensive changes to fishing techniques, such as slightly larger hooks and traps from which sea turtles can escape, can dramatically cut the mortality rate.^[25][26] Turtle Excluder Devices (TEDs) have reduced sea turtle bycatch in shrimp nets by 97 percent. Another danger comes from marine debris, especially from abandoned fishing nets in which they can become entangled.

Beach development is another area which threatens sea turtles. Since many sea turtles return to the same beach each time to nest, development can disrupt the cycle. There has been a movement to protect these areas, in some cases by special police. In some areas, such as the east coast of Florida, conservationists dig up sea turtle eggs and relocate them to fenced nurseries to protect them from beach traffic.

Since hatchlings find their way to the ocean by crawling towards the brightest horizon, they can become disoriented on developed stretches of coastline. Lighting restrictions can prevent lights from shining on the beach and confusing hatchlings. Sea turtle-safe lighting uses red or amber LED light, invisible to sea turtles, in place of white light.

Another major threat to sea turtles is black-market trade in eggs and meat. This is a problem throughout the world, but especially a concern in the Philippines, India, Indonesia and the coastal nations of Latin America. Estimates reach as high as 35,000 sea turtles killed a year in Mexico and the same number in Nicaragua. Conservationists in Mexico and the United States have launched "Don't Eat Sea Turtle" campaigns in order to reduce this trade in sea turtle products. These campaigns have involved figures such as Dorismar, Los Tigres del Norte and Maná. Sea turtles are often consumed during the Catholic season of Lent, even though they are reptiles, not fish. Consequently, conservation organizations have written letters to the Pope asking that he declare sea turtles meat.^{[citation needed]}

Climate change may also cause a threat to sea turtles. Since sand temperature at nesting beaches defines the sex of a sea turtle while developing in the egg, there is concern that rising temperatures may produce too many females. However, more research is needed to understand how climate change might affect sea turtle gender distribution and what other possible threats it may pose.^[27]

Fibropapillomatosis disease causes tumors in sea turtles.

Injured sea turtles are sometimes rescued and rehabilitated by professional organizations, such as The Loggerhead Marinelife Center in Juno Beach, FL, The Turtle Hospital in Marathon, Florida, the Mote Marine Laboratory in Sarasota, Florida, the Marine Mammal Center in Northern California, the Clearwater Marine Aquarium in Clearwater, Florida,^[28] and the Sea Turtle Inc. organization in South Padre Island, Texas.^[29][30] One such sea turtle, named Nickel for the coin that was found lodged in her throat, lives at the Shedd Aquarium in Chicago.

In the Caribbean, researchers are having some success in assisting a comeback.^[31] In September 2007, Corpus Christi, Texas, wildlife officials found 128 Kemp's ridley sea turtle nests on Texas beaches, a record number, including 81 on North Padre Island (Padre Island National Seashore) and four on Mustang Island. Wildlife officials released 10,594 Kemp's ridleys hatchlings along the Texas coast this year.

Also in 2007, the U.S. Fish and Wildlife Service and the National Marine Fisheries Service issued a determination that the leatherback, the hawksbill and the Kemp's Ridley populations were endangered while that of green sea turtles and olive ridleys were threatened.^[32]

In Southeast Asia, the Philippines has had several initiatives dealing with the issue of sea turtle conservation. In 2007, the province of Batangas in the Philippines declared the catching and eating of Pawikans illegal. However, the law seems to have had little effect as Pawikan eggs are still in demand in Batangan markets. In September 2007, several Chinese poachers were apprehended off the Turtle Islands in the country's southernmost province of Tawi-Tawi. The poachers had collected more than a hundred sea turtles, along with 10,000 sea turtle eggs.^[33]

Evaluating the progress of conservation programs is difficult, because many sea turtle populations have not been assessed adequately.^[34] Most information on sea turtle populations comes from counting nests on beaches, but this doesn’t provide an accurate picture of the whole sea turtle population.^[35] A 2010 United States National Research Council report concluded that more detailed information on sea turtles’ life cycles, such as birth rates and mortality, is needed.^[36]