The hawksbill turtle (Eretmochelys imbricata) is a critically endangered sea turtle belonging to the family Cheloniidae. It is the only species in its genus. The species has a worldwide distribution, with Atlantic and Pacific subspecies. Eretmochelys imbricata imbricata is the Atlantic subspecies, while Eretmochelys imbricata bissa is found in the Indo-Pacific region.^[1]

The hawksbill's appearance is similar to that of other marine turtles. It has a generally flattened body shape, a protective carapace, and its flipper-like arms are adapted for swimming in the open ocean. E. imbricata is easily distinguished from other sea turtles by its sharp, curving beak with prominent tomium, and the saw-like appearance of its shell margins. While the turtle lives a part of its life in the open ocean, it is most often encountered in shallow lagoons and coral reefs where it feeds on its chosen prey, sea sponges. Some of the sponges eaten by E. imbricata are known to be highly toxic and lethal when eaten by other organisms. In addition, the sponges that hawksbills eat are usually those with high silica content, making the turtles one of few animals capable of eating siliceous organisms. They also feed on other invertebrates, such as comb jellies and jellyfish.^[2]

Because of human fishing practices, Eretmochelys imbricata populations around the world are threatened with extinction and the turtle has been classified as critically endangered by the World Conservation Union.^[3] Several countries, such as China and Japan, have valued hunting hawksbill turtles for their flesh, which is considered good eating. Hawksbill turtle shells are the primary source of tortoise shell material, used for decorative purposes. By the Convention on International Trade in Endangered Species, it is illegal to capture and to trade in hawksbill turtles and products derived from them in many nations.^[4]

Anatomy and morphology

Eretmochelys imbricata. The carapace's serrated margin and overlapping scutes are evident in this individual.

The hawksbill turtle has several characteristics that distinguish it from other, closely-related species. Its elongated, tapered head ends in a beak-like mouth (from which its common name is derived), its beak more sharply pronounced and hooked than other sea turtles. The hawksbill's arms have two visible claws on each flipper.

A close-up of the hawksbill's distinct beak.

Distribution

Another model of the possible distribution of E. imbricata. Red circles represent known major nesting sites. Yellow circles are minor nesting sites.

Atlantic subpopulation

A hawksbill turtle in Saba, Netherlands Antilles.

In the Caribbean, they are known from the Brazilian coast (specifically Bahia), southern Florida and Hawaii. They have also been seen on the beaches of Antigua and Barbuda.^[6] Costa Rica has its share of E. imbricata nesting sites, specifically in the vicinity of Tortuguero.^[13] The island of Cuba is a known feeding ground for the Caribbean hawksbill turtle population.^[14] In Puerto Rico, the waters around Mona Island serve as feeding grounds for Caribbean E. imbricata.^[15] While a tropical species, E. imbricata has been found in areas in the United States within higher latitudes, such as Massachusetts and Long Island Sound.^[12] They have also been seen in the waters off Virginia .^[2]

Indo-Pacific subpopulation

The species' Indo-Pacific population is widespread throughout the entire region. In the Indian Ocean, hawksbills are a common sight all along the east coast of the African continent, including the seas surrounding Madagascar and nearby island groups. The species' Indian Ocean range stretches all the way along the coast of Asia, including the Persian Gulf and the Red Sea, along the entire coast of the Indian subcontinent, across the entire Indonesian archipelago and the northwestern coast of Australia. The Pacific range of E. imbricata is somewhat limited to the ocean's tropical and subtropical regions. Its northernmost reach in the region are the waters off the southwestern tip of the Korean peninsula and the Japanese archipelago. The range continues, enveloping the entire region of Southeast Asia, the entire northern coast of Australia all the way south to the northern part of New Zealand. Across the Pacific, hawksbills are known as far north as the Baja peninsula in Mexico, along the waters off the Central American and South American coast to the northern tip of Chile.^[10]

In the Philippines, there are several known nesting sites for the species. Hawksbill turtle hatchlings have been found on the island of Boracay.^[16] A small group of islands in the southwest of the archipelago have been named the "Turtle Islands" precisely because they are known nesting grounds for two species of sea turtle, including Eretmochelys imbricata. (The other being the green sea turtle, Chelonia mydas.)^[17] In Australia, E. imbricata are known to nest on Milman Island in the Great Barrier Reef.^[18] In the Indian Ocean, hawksbill turtles have been found to nest as far west as Cousine Island in the Seychelles, where the species has been legally protected since 1994. The Seychelles' inner islands and islets, such as Aldabra Island, are ripe feeding grounds for immature hawksbills.^[8][19]

Ecology and life history

Habitat

Adult hawksbill turtles are primarily found in tropical coral reefs. They are usually seen resting in caves and ledges in and around these reefs, throughout the day. As a highly migratory species, they have also been encountered in a wide range of habitats, from the open ocean to lagoons and even mangrove swamps in estuaries.^[6][20] While much is not known about the habitat preferences of early-life stage E. imbricata, like other sea turtles' young, they are assumed to be completely pelagic and thus make the open sea their home until they mature.^[21]

Feeding ecology

E. imbricata in a coral reef in Tortuga.

Eretmochelys imbricata have shown themselves to be highly resilient and resistant to their prey. Some of the sponges known to be eaten by hawksbills, such as Aaptos aaptos, Chondrilla nucula, Tethya actinia, Spheciospongia vesparum and Suberites domuncula, are highly (often lethally) toxic to other organisms. In addition, hawksbills are known to choose sponge species that have a significant amount of siliceous spicules, such as Ancorina, Geodia, Ecionemia and Placospongia.^[22]

Life history

Young E. imbricata from Réunion Island.

The baby turtles, usually weighing less than two dozen grams, hatch during the night after around two months. These newly-emergent hatchlings are darkly-colored, with heart-shaped carapaces measuring around 2.5 centimeters (1 in) long. They instinctually head for the sea, attracted by the reflection of the moon on the water (a mechanism which can be disrupted by anthropogenic light sources such as street lamps and lights). While they emerge under the cover of darkness, baby turtles that do not reach the water by daybreak are preyed upon by predators such as shorebirds and shore crabs.^[6]

E. imbricata hatchling in Grenada.

While there is no clear consensus because of a lack of data, hawksbill turtles are believed to live from thirty to fifty years in the wild.^[24] Like other sea turtles, hawksbill turtles are solitary for most of their lives, they only group together to mate. They were once thought to be habitual, but they are now known to be highly migratory.^[23] Because of their tough carapaces, hawksbill turtles have no major predators as there are few creatures that are capable of biting through their protective shell. Sharks and estuarine crocodiles are a few of their natural predators. Octopuses and some species of pelagic fish have also been known to prey on the adult turtles.^[23]

Evolutionary history

Within the sea turtles, Eretmochelys imbricata has several unique anatomical and ecological traits, including being the only primarily spongivorous reptile known. Because of this, its evolutionary position has been somewhat unclear. Molecular analyses supports the probability that the Eretmochelydae evolved from carnivorous ancestors rather than herbivorous ones. As the taxonomic tribe Carettini is composed of carnivorous species (such as the loggerhead turtle), the hawksbill most probably evolved from them instead of the herbivorous Chelonini, which includes the green turtle.^[25]

Etymology and taxonomic history

Hawksbill turtle (top right) in a 1904 plate by Ernst Haeckel.

There are two accepted subspecies in the E. imbricata taxon. Eretmochelys imbricata bissa (Rüppell, 1835) refers to all known populations of the Eretmochelys imbricata that reside in the Pacific Ocean.^[28] The Atlantic population has been found to be a separate subspecies, Eretmochelys imbricata imbricata (Linnaeus, 1766). The subspecies name of imbricata was retained because the type specimen that Linnaeus used to initially describe the species was from the Atlantic.^[29]

Fitzinger derived the genus' name, Eretmochelys from the Greek roots eretmo and chelys, corresponding to "oar" and "turtle" respectively. The name refers to the turtles' oar-like front flippers. The species' name imbricata is Latin, corresponding to the English term imbricate. This appropriately describes the turtles' overlapping posterior scutes. The Pacific hawksbill's subspecies name, bissa is Latin for "double". The subspecies was originally described as Caretta bissa and the term referred to the then-species' being the second species in the genus.^[30] Caretta is the genus of the hawksbill's much larger relative, the loggerhead turtle.

Importance to humans

A Japanese tortoiseshell ornament.

Many cultures also use the turtles' shells for decoration. In China where it was known as tai mei, it is called the tortoise-shell turtle, named primarily for its shell which was used for decoration.^[32] In Japan, the turtles are also harvested for their shell scutes, which are called bekko in the local Nihongo. It is used in various personal implements, such as eyeglass frames. In 1994, Japan stopped importing hawksbill shells from other nations. Prior to this, the Japanese hawksbill shell trade was around 30,000 kilograms of raw shells per year.^[14][33] In the west, hawksbill turtle shells have been harvested by the ancient Greeks and ancient Romans for jewelry, such as combs, brushes and rings.^[34] A bulk of the world's hawksbill turtle shell trade is harvested from the Caribbean. In 2006, it was found that processed shells of the turtles are regularly available, often in large amounts in countries in the region, including the Dominican Republic and Colombia.^[35]

Hawksbills in art and literature

A much-beloved fountain sculpture of a boy riding a hawksbill affectionately known as Turtle Boy stands in Worcester, Massachusetts.

Conservation

General consensus has determined sea turtles, including Eretmochelys imbricata to be at the very least, threatened species because of their long lifespans, slow growth and maturity, and slow reproductive rates. Many adult turtles have been killed by humans both deliberately and incidentally. In addition, the nesting sites of the turtles are also threatened by human and animal encroachment. Small mammals have been known to raid the nesting sites and dig up the turtles' eggs.^[6] In the U.S. Virgin Islands, Eretmochelys imbricata nests (along with the nests of other sea turtles like Dermochelys coriacea) are often raided by mongooses right after being laid.^[36]

A hawksbill turtle in Tobago.

Historically, Eretmochelys imbricata was first listed as endangered by the IUCN in 1982.^[38] This endangered status continued all the way through several reassessments in 1986,^[39] 1988,^[40] 1990^[41] and 1994^[42] until it was upgraded in status to critically endangered in 1996 (see above).

The species (along with the entire family Cheloniidae) has been listed on Appendix I of the Convention on International Trade in Endangered Species.^[4] It is illegal to import or export turtle products, kill, capture or harass hawksbill turtles.^[31]

Local involvement in the conservation efforts for the species have also increased in the past few years. The United States Fish and Wildlife Service has classified the hawksbill turtle as endangered since 1970. The U.S. government has several recovery plans in place for protecting its populations of E. imbricata.^[43]

Cultural References

The Hawksbill Turtle is depicted on the reverse side of the 20-Venezuelan bolívar and the 2-Brazilian Reais banknotes.

References

See also

• Chelonioidea. The sea turtle superfamily.
• Caretta caretta. The loggerhead turtle.
• Chelonia mydas. The green turtle.
• Dermochelys coriacea. The leatherback turtle.
• Lepidochelys kempii. The Kemp's Ridley turtle.
• Lepidochelys olivacea. The olive ridley turtle.
• Natator depressus. The flatback turtle.

External links

• Florida Sea Turtle information Florida Fish and Wildlife Conservation Commission Fish and Wildlife Research Institute
• WWF-Malaysia's Hawksbill Turtles Satellite Telemetry Website WWF-Malaysia's website featuring the journey of two satellite tracked hawksbill turtles and other information about hawksbill turtles in the region of Malacca, Malaysia.
• Seaturtle.org Home to sea turtle conservation efforts such as the Marine Turtle Research Group and publisher of the Marine Turtle Newsletter.

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