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| synonyms = <small>''Eretmochelys imbricata squamata'' [[junior synonym]]</small>
| synonyms = <small>''Eretmochelys imbricata squamata'' [[junior synonym]]</small>
}}
}}
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 Ocean|Atlantic]] and [[Pacific Ocean|Pacific]] [[subspecies]]. ''Eretmochelys imbricata imbricata'' is the Atlantic subspecies, while ''Eretmochelys imbricata bissa'' is found in the Indo-Pacific region.<ref name="ITIS">{{ITIS|ID=173836|taxon=Eretmochelys imbricata|year=2007|date=5 February}}</ref>
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 Ocean|Atlantic]] fart [[Pacific Ocean|Pacific]] [[subspecies]]. ''Eretmochelys imbricata imbricata'' is the Atlantic subspecies, while ''Eretmochelys imbricata bissa'' is found in the Indo-Pacific region.<ref name="ITIS">{{ITIS|ID=173836|taxon=Eretmochelys imbricata|year=2007|date=5 February}}</ref>


The hawksbill's appearance is similar to that of other marine turtles. It has a generally flattened body shape, a protective [[Carapace#Turtles and tortoises|carapace]], and its [[flipper (anatomy)|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 [[serration|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 reef]]s where it feeds on its primary 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 [[Ctenophora|comb jellies]] and [[jellyfish]].<ref name="VDGIF"/>
The hawksbill's appearance is similar to that of other marine turtles. It has a generally flattened body shape, a protective [[Carapace#Turtles fart tortoises|carapace]], fart its [[flipper (anatomy)|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]], fart the [[serration|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 reef]]s where it feeds on its primary prey, [[sea sponges]]. Some of the sponges eaten by ''E. imbricata'' are known to be highly toxic fart 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 [[Ctenophora|comb jellies]] and [[jellyfish]].<ref name="VDGIF"/>


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 [[IUCN|World Conservation Union]].<ref name="IUCN"/> 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 ''[[tortoiseshell material|tortoise shell]]'' material, used for decorative purposes. By the [[Convention on International Trade in Endangered Species]], it is illegal in many nations to capture and to trade in hawksbill turtles and products derived from them.<ref name="CITESAPP"/>
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 [[IUCN|World Conservation Union]].<ref name="IUCN"/> 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 ''[[tortoiseshell material|tortoise shell]]'' material, used for decorative purposes. By the [[Convention on International Trade in Endangered Species]], it is illegal in many nations to capture and to trade in hawksbill turtles and products derived from them.<ref name="CITESAPP"/>

Revision as of 20:20, 24 January 2010

Hawksbill Turtle
Eretmochelys imbricata in Útila.
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Reptilia
Order:
Testudines
Family:
Cheloniidae
Genus:
Eretmochelys
Species:
E. imbricata
Binomial name
Eretmochelys imbricata
(Linnaeus, 1766)
subspecies

Eretmochelys imbricata bissa (Rüppell, 1835)
Eretmochelys imbricata imbricata (Linnaeus, 1766)

Range of the Hawksbill turtle
Synonyms

Eretmochelys imbricata squamata junior synonym

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 fart Pacific subspecies. Eretmochelys imbricata imbricata is the Atlantic subspecies, while Eretmochelys imbricata bissa is found in the Indo-Pacific region.[2]

The hawksbill's appearance is similar to that of other marine turtles. It has a generally flattened body shape, a protective carapace, fart 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, fart 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 primary prey, sea sponges. Some of the sponges eaten by E. imbricata are known to be highly toxic fart 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.[3]

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.[1] 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 in many nations to capture and to trade in hawksbill turtles and products derived from them.[4]

Anatomy and morphology

Eretmochelys imbricata has the typical appearance of a marine turtle. Like the other members of its family, it has a depressed body form and flipper-like limbs adapted for swimming.

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

Adult hawksbill turtles have been known to grow up to a meter (3.3 feet) in length, weighing around 80 kilograms (175 lb) on average. The heaviest hawksbill ever captured was measured to be 127 kilograms (280 lb).[3] The turtle's shell, or carapace, has an amber background patterned with an irregular combination of light and dark streaks, with predominantly black and mottled brown colors radiating to the sides.[5]

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), and its beak is 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.

One of the hawksbill's more-easily distinguished characteristics is the pattern of the thick scutes that make up its carapace. While its carapace has five central scutes and four pairs of lateral scutes like several members of the same family, E. imbricata's posterior scutes overlap in such a way as to give the rear margin of its carapace a serrated look, similar to the edge of a saw or a steak knife. The turtle's carapace itself has been known to reach almost a meter in length.[6]

The sand tracks of hawksbill turtles are asymmetrical, as they crawl on land with an alternating gait. This is as opposed to the green sea turtle and the leatherback turtle, which crawl rather symmetrically.[7][8]

Due to its consumption of venomous cnidarians, hawksbill turtle flesh can reach certain levels of toxicity.[9]

Distribution

Hawksbill turtles have a wide range, found predominantly in tropical reefs of the Indian, Pacific and Atlantic oceans. Of all the sea turtle species, E. imbricata is the one most associated with tropical waters. Two major subpopulations are acknowledged to exist, the Atlantic and Indo-Pacific subpopulations.[10]

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 Atlantic, E. imbricata populations can be seen as far west as the Gulf of Mexico and as far southeast as the Cape of Good Hope in South Africa.[11][10][12] They are known from the Brazilian coast (specifically Bahia) through southern Florida and the waters off Virginia.[3] The species' range extends as far north as Long Island Sound and Massachusetts[13] in the west Atlantic and the frigid waters of the English Channel in the east (the species' northernmost sighting to date).

In the Caribbean, they have been seen nesting on beaches of Antigua and Barbuda[6] and in the vicinity of Tortuguero in Costa Rica.[12] The waters off Cuba[14] and around Mona Island near Puerto Rico [15] are known feeding grounds.

Indo-Pacific subpopulation

The species' Indo-Pacific population is widespread. In the Indian Ocean, hawksbills are a common sight all along the east coast of Africa, including the seas surrounding Madagascar and nearby island groups, and all the way along the southern Asian coast, including the Persian Gulf, the Red Sea, and the coasts of the Indian subcontinent and Southeast Asia. They are present across the Indonesian archipelago and northern Australia. The Pacific range of E. imbricata is limited to the ocean's tropical and subtropical regions. In the west, it extends from the southwestern tips of the Korean peninsula and the Japanese archipelago down to northern New Zealand. In the east Pacific, hawksbills are known from the Baja peninsula in Mexico south along the coast to northern 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 has been named the "Turtle Islands" precisely because they are known nesting grounds for two species of sea turtle, including Eretmochelys imbricata (the other being Chelonia mydas, the green turtle).[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 Venezuela.

While they are known to be omnivorous, the principal food of hawksbill turtles is sponges. Sponges constitute 70 – 95% of the diets of E. imbricata populations in the Caribbean. However, like many spongivores, E. imbricata feed only on a few select species and will ignore many others. The Caribbean hawksbill populations were found to feed primarily on sponges from the class Demospongiae, specifically ones belonging to the orders Astrophorida, Spirophorida and Hadromerida.[22] Select sponge species known to be fed on by these turtles include Geodia gibberosa.[3] Aside from sponges, hawksbills also feed on algae and cnidarians like jellyfish and sea anemones.[6] The hawksbill is also known to feed on the dangerous jellyfish-like hydrozoan, the Portuguese Man o' War (Physalia physalis). Hawksbills close their unprotected eyes when they feed on these cnidarians, for a Man o' War's stinging cells cannot penetrate the turtles' armoured heads.[3]

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 vesparium 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.

Much is not known about the life history of Eretmochelys imbricata.[23] Hawksbills are known to mate biyearly in secluded lagoons in remote islands throughout their range. Mating season for Atlantic hawksbills usually takes place from April to November. For Indian Ocean populations such as the Seychelles hawksbill population, the mating season is from September to February.[8] As with other sea turtles, hawksbills mate in shallow lagoons off the shores of their prospective nesting beaches. After mating, the females drag their heavy bodies high onto the beach during the night. They will then clear out an area and dig a nesting hole using their rear flippers. The female then lays a clutch of eggs in the nest and then covers them with sand. Caribbean and Florida nests of E. imbricata normally contain around 140 eggs. After the several-hour-long process, the female then returns to the sea. This is the only time when hawksbill turtles are known to leave the ocean.[6][11]

The baby turtles, usually weighing less than two dozen grams, hatch during the night after around two months. These newly emergent hatchlings are dark-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 Puerto Rico.

The early life history of juvenile hawksbill turtles is unknown. Upon reaching the sea, the hatchlings are assumed to enter a pelagic life stage (like other marine turtles) for an undetermined amount of time. While hawksbill turtle growth rates are not known, when E. imbricata juveniles reach around 35 cm, they switch from a pelagic life style to a coral reef-associated one. Hawksbill turtles are hypothesized to reach maturity after thirty years.[11]

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 group together only 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 few creatures are capable of biting through their protective shell. Sharks and estuarine crocodiles are the best recognized 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 support placement of Eretmochelys within the taxonomic tribe Carettini, which includes the carnivorous loggerhead and ridley sea turtles, rather than in the tribe Chelonini, which includes the herbivorous green turtle. The hawksbill thus probaby evolved from carnivorous ancestors.[25]

Etymology and taxonomic history

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

The hawksbill turtle was originally described by Carolus Linnaeus as Testudo imbricata in 1766.[26] It was moved into the genus Eretmochelys by the Austrian zoologist Leopold Fitzinger in 1843.[27] In 1857, the species was redescribed as Eretmochelys imbricata squamata, a designation that is now invalid.[28]

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.[29] 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.[30]

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; the term referred to the then-species being the second species in the genus.[31] Caretta is the genus of the hawksbill's much larger relative, the loggerhead turtle.

Importance to humans

A Japanese tortoiseshell ornament.

Throughout the world, hawksbill turtles are taken by humans even though it is illegal to hunt them in many countries.[32] In some parts of the world, hawksbill turtles are taken and eaten as a delicacy. As far back as the fifth century B.C., sea turtles including the hawksbill were eaten as delicacies in China.[33]

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.[33] In Japan, the turtles are also harvested for their shell scutes, which are called bekko in Japanese. 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 (66,000 lb) of raw shells per year.[14][34] In the West, hawksbill turtle shells were harvested by the ancient Greeks and ancient Romans for jewelry, such as combs, brushes and rings.[35] The 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.[36]

The hawksbill turtle is depicted on the reverse side of the 20-Venezuelan bolívar and the 2-Brazilian Reais banknotes. 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 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.[37]

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

File:Hawksbill Turtle 1.JPG.jpg
A hawksbill turtle in Tobago.

In 1996, the IUCN Red List of Threatened Species classified Eretmochelys imbricata as critically endangered.[1] Its status as an endangered species was challenged prior to this, with two petitions claiming that the turtle (along with three other species) had several significant stable populations worldwide. These petitions were rejected by the IUCN based on their analysis of data submitted by the Marine Turtle Specialist Group (MTSG). The data given by the MTSG showed that the worldwide population of hawksbill turtles had been reduced by 80% in the last three of the species' generations, and that there was no significant increase in the turtles' populations as of 1996. In light of this data, the IUCN applied the critically endangered (A1) status upon the species. CR A2 status was denied however, because the IUCN believed that there were insufficient data to show that the population of hawksbill turtles were likely to decrease by a further 80% in the future.[43]

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, or to kill, capture, or harass hawksbill turtles.[32]

Local involvement in the conservation efforts for the species has also increased in the past few years. The United States Fish and Wildlife Service and National Marine Fisheries Service have classified the hawksbill turtle as endangered under the Endangered Species Act since 1970. The U.S. government has several recovery plans in place for protecting its populations of E. imbricata.[44]

See also

References

  1. ^ a b c Template:IUCN2006
  2. ^ "Eretmochelys imbricata". Integrated Taxonomic Information System. 5 February. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
  3. ^ a b c d e "Species Booklet: Hawksbill sea turtle". Virginia Fish and Wildlife Information Service. Virginia Department of Game & Inland Fisheries. Retrieved 2007-02-06.
  4. ^ a b CITES (2006-06-14). "Appendices" (SHTML). Convention on International Trade in Endangered Species of Wild Flora and Fauna. Retrieved 2007-02-05.
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