Hawksbill sea turtle
The hawksbill sea turtle (Eretmochelys imbricata) is a critically endangered sea turtle belonging to the familyCheloniidae. It is the only extant species in its genus. The species has a worldwide distribution, with Atlantic andPacific subspecies. E. imbricata imbricata is the Atlantic subspecies, while E. imbricata bissa is found in the Indo-Pacific region.
The hawksbill's appearance is similar to that of other marine turtles. It has a generally flattened body shape, a protective carapace, and flipper-like arms, 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. Hawksbill shells slightly change colors, depending on water temperature. While this turtle lives part of its life in the open ocean, it spends more time in shallow lagoons and coral reefs.
Human fishing practices threaten E. imbricata populations with extinction. The World Conservation Union. classifies the Hawksbill as critically endangered. Hawksbill shells are the primary source of tortoise shell material, used for decorative purposes. The Convention on International Trade in Endangered Species outlaws the capture and trade of hawksbill sea turtles and products derived from them.
The hawksbill's appearance is similar to that of other marine turtles. It has a generally flattened body shape, a protective carapace, and flipper-like arms, 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. Hawksbill shells slightly change colors, depending on water temperature. While this turtle lives part of its life in the open ocean, it spends more time in shallow lagoons and coral reefs.
Human fishing practices threaten E. imbricata populations with extinction. The World Conservation Union. classifies the Hawksbill as critically endangered. Hawksbill shells are the primary source of tortoise shell material, used for decorative purposes. The Convention on International Trade in Endangered Species outlaws the capture and trade of hawksbill sea turtles and products derived from them.
Anatomy and morphology
E. 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.
Adult hawksbill sea turtles have been known to grow up to 1 metre (3 ft) in length, weighing around 80 kilograms (180 lb) on average. The heaviest hawksbill ever captured was measured to be 127 kilograms (280 lb). 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.
The hawksbill sea turtle has several characteristics that distinguish it from other sea turtle 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 others. The hawksbill's arms have two visible claws on each flipper.
Adult hawksbill sea turtles have been known to grow up to 1 metre (3 ft) in length, weighing around 80 kilograms (180 lb) on average. The heaviest hawksbill ever captured was measured to be 127 kilograms (280 lb). 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.
The hawksbill sea turtle has several characteristics that distinguish it from other sea turtle 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 others. The hawksbill's arms have two visible claws on each flipper.
One of the hawksbill's more easily distinguished characteristics is the pattern of thick scutes that make up its carapace. While its carapace has five central scutes and four pairs of lateral scutes like several members of its 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 has been known to reach almost 1 metre (3 ft) in length.
Hawksbill sea turtles' sand tracks are asymmetrical, because they crawl on land with an alternating gait. By contrast, the green sea turtle and theleatherback turtle crawl rather symmetrically.
Due to its consumption of venomous cnidarians, hawksbill sea turtle flesh can become toxic.
Hawksbill sea turtles' sand tracks are asymmetrical, because they crawl on land with an alternating gait. By contrast, the green sea turtle and theleatherback turtle crawl rather symmetrically.
Due to its consumption of venomous cnidarians, hawksbill sea turtle flesh can become toxic.
Habitat
Adult hawksbill sea 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 inhabit a wide range of habitats, from the open ocean to lagoons and even mangrove swamps in estuaries. While little is known about the habitat preferences of early-life stage E. imbricata, like other sea turtles' young, they are assumed to be completely pelagic, remaining at sea until they mature.
Feeding
While they are omnivorous, sea sponges are the principal food of hawksbill sea turtles. Sponges constitute 70–95% of their diets in the Caribbean. However, like many spongivores, E. imbricata feed only on select species, ignoring many others. Caribbean hawksbill populations feed primarily on the orders Astrophorida, Spirophorida, and Hadromerida in the class Demospongiae. Select sponge species known to be fed on by these turtles include Geodia gibberosa.
Aside from sponges, hawksbills feed on algae and cnidarians comb jellies and other jellyfish and sea anemones. The hawksbill also feeds on the dangerous jellyfish-like hydrozoan, the Portuguese Man o' War (Physalia physalis). Hawksbills close their unprotected eyes when they feed on these cnidarians. The Man o' War's stinging cells cannot penetrate the turtles' armored heads.
E. imbricata are highly resilient and resistant to their prey. Some of the sponges 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 choose sponge species that have a significant amount ofsiliceous spicules, such as Ancorina, Geodia, Ecionemia, and Placospongia.
Aside from sponges, hawksbills feed on algae and cnidarians comb jellies and other jellyfish and sea anemones. The hawksbill also feeds on the dangerous jellyfish-like hydrozoan, the Portuguese Man o' War (Physalia physalis). Hawksbills close their unprotected eyes when they feed on these cnidarians. The Man o' War's stinging cells cannot penetrate the turtles' armored heads.
E. imbricata are highly resilient and resistant to their prey. Some of the sponges 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 choose sponge species that have a significant amount ofsiliceous spicules, such as Ancorina, Geodia, Ecionemia, and Placospongia.
Life history
Not much is known about the life history of E. imbricata. The life history of sea turtles can be divided into three phases, namely the pelagic phase running from hatching to about 20 cm, the benthic phase, when the immature turtles recruit to foraging areas and the reproductive phase when turtles reach sexual maturity. The pelagic phase possibly lasts 1 to 4 years. Hawksbills show a degree of fidelity after recruiting to the benthic phase, however movement to other similar habitats is possible.
Breeding
Hawksbills mate biannually in secluded lagoons off their nesting beaches in remote islands throughout their range. Mating season for Atlantic hawksbills usually spans April to November. Indian Ocean populations such as theSeychelles hawksbill population, mate from September to February. After mating, females drag their heavy bodies high onto the beach during the night. They clear an area of debris and dig a nesting hole using their rear flippers. The female then lays a clutch of eggs and covers them with sand. Caribbean and Florida nests of E. imbricata normally contain around 140 eggs. After the hours-long process, the female then returns to the sea.
The baby turtles, usually weighing less than 24 grams (0.85 oz) hatch at night after around two months. These newly emergent hatchlings are dark-colored, with heart-shaped carapaces measuring around 2.5 centimeters (0.98 in) long. They instinctively walk into the sea, attracted by the reflection of the moon on the water (possibly disrupted by 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 shorebirds, shore crabs, and other predators.
The baby turtles, usually weighing less than 24 grams (0.85 oz) hatch at night after around two months. These newly emergent hatchlings are dark-colored, with heart-shaped carapaces measuring around 2.5 centimeters (0.98 in) long. They instinctively walk into the sea, attracted by the reflection of the moon on the water (possibly disrupted by 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 shorebirds, shore crabs, and other predators.
Early life
The early life history of juvenile hawksbill sea 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 sea turtle growth rates are not known, when E. imbricata juveniles reach around 35 centimeters (14 in) they switch from a pelagic life style to living on coral reefs.
Maturity
Hawksbills evidently reach maturity after thirty years. They are believed to live from thirty to fifty years in the wild.Like other sea turtles, hawksbills are solitary for most of their lives; they meet only to mate. They are highlymigratory. Because of their tough carapaces, adults' only predators are sharks, estuarine crocodiles, octopuses, and some species of pelagic fish.
A series of biotic and abiotic cues, such as individual genetics, foraging quantity and quality or population density, may trigger the maturation of the reproductive organs and the production of gametes and thus determine sexual maturity. Like many reptiles, it is highly unlikely that all marine turtles of a same aggregation reach sexual maturity at the same size and thus age. Age at maturity has been estimated between 10 and 25 years for Caribbean hawksbills. Turtles nesting in the Indo-Pacific region may reach maturity at a minimum of 30 to 35 years.
A series of biotic and abiotic cues, such as individual genetics, foraging quantity and quality or population density, may trigger the maturation of the reproductive organs and the production of gametes and thus determine sexual maturity. Like many reptiles, it is highly unlikely that all marine turtles of a same aggregation reach sexual maturity at the same size and thus age. Age at maturity has been estimated between 10 and 25 years for Caribbean hawksbills. Turtles nesting in the Indo-Pacific region may reach maturity at a minimum of 30 to 35 years.
Evolutionary history
Within the sea turtles, E. imbricata has several unique anatomical and ecological traits. It is the only primarily spongivorous reptile. Because of this, its evolutionary position is somewhat unclear. Molecular analyses support placement of Eretmochelys within the taxonomic tribe Carettini, which includes the carnivorousloggerhead and ridley sea turtles, rather than in the tribe Chelonini, which includes the herbivorous green turtle. The hawksbill probably evolved from carnivorous ancestors.
Etymology and taxonomic history
Linnaeus originally described the hawksbill sea turtle as Testudo imbricata in 1766, i nthe 12th edition of his Systema Naturae. In 1843 Austrian zoologist Leopold Fitzinger moved it into genus Eretmochelys. In 1857, the species was temporarily misdescribed as Eretmochelys imbricata squamata.
There are two accepted subspecies in E. imbricata's taxon. E. imbricata bissa (Rüppell, 1835) refers to populations that reside in the Pacific Ocean. The Atlantic population is a separate subspecies, E. imbricata imbricata (Linnaeus, 1766). The nominate subspecies is the Atlantic taxon, because Linnaeus' type specimen was from the Atlantic.
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. Caretta is the genus of the hawksbill's much larger relative, the loggerhead turtle.
There are two accepted subspecies in E. imbricata's taxon. E. imbricata bissa (Rüppell, 1835) refers to populations that reside in the Pacific Ocean. The Atlantic population is a separate subspecies, E. imbricata imbricata (Linnaeus, 1766). The nominate subspecies is the Atlantic taxon, because Linnaeus' type specimen was from the Atlantic.
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. Caretta is the genus of the hawksbill's much larger relative, the loggerhead turtle.
Importance to humans
Throughout the world, hawksbill sea turtles are taken by humans even though it is illegal to hunt them in many countries. In some parts of the world, hawksbill sea turtles are eaten as a delicacy. As far back as the fifth century B.C., sea turtles including the hawksbill were eaten as delicacies in China.
Many cultures also use turtles' shells for decoration. These turtles have been harvested for their beautiful shell since Egyptian times. In China, where it was known as tai mei, the Hawksbill is called the tortoise-shell turtle, named primarily for its shell, which was used for decoration. 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; the fashion style known as"tortoiseshell". 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. In the West, hawksbill sea turtle shells were harvested by the ancient Greeks and ancient Romans for jewelry, such as combs, brushes, and rings. The bulk of the world's hawksbill sea turtle shell trade originates in the Caribbean. In 2006, processed shells were regularly available, often in large amounts, in nearby countries, including the Dominican Republicand Colombia.
The hawksbill sea turtle appears 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.
Many cultures also use turtles' shells for decoration. These turtles have been harvested for their beautiful shell since Egyptian times. In China, where it was known as tai mei, the Hawksbill is called the tortoise-shell turtle, named primarily for its shell, which was used for decoration. 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; the fashion style known as"tortoiseshell". 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. In the West, hawksbill sea turtle shells were harvested by the ancient Greeks and ancient Romans for jewelry, such as combs, brushes, and rings. The bulk of the world's hawksbill sea turtle shell trade originates in the Caribbean. In 2006, processed shells were regularly available, often in large amounts, in nearby countries, including the Dominican Republicand Colombia.
The hawksbill sea turtle appears 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 E. 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 accidentally. In addition, human and animal encroachment threatens nesting sites and small mammals dig up eggs. In the U.S. Virgin Islands, mongooses raid Hawksbill nests (along with those of other sea turtles like Dermochelys coriacea) right after they are laid.
In 1982 the IUCN Red List of Threatened Species first listed E. imbricata as endangered. This endangered status continued through several reassessments in 1986, 1988, 1990, and 1994 until it was upgraded in status tocritically endangered in 1996. Two petitions challenged its status as an endangered species prior to this, claiming that the turtle (along with three other species) had several significant stable populations worldwide. These petitions were rejected based on their analysis of data submitted by the Marine Turtle Specialist Group (MTSG). The data given by the MTSG showed that the worldwide hawksbill sea turtle population had declined by 80% in the three most recent generations, and that there was no significant population increase as of 1996. CR A2 status was denied however, because the IUCN did not find sufficient data to show the population likely to decrease by a further 80% in the future.
The species (along with the entire family Cheloniidae) has been listed on Appendix I of the Convention on International Trade in Endangered Species. It is illegal to import or export turtle products, or to kill, capture, or harass hawksbill sea turtles.
Local involvement in conservation efforts has also increased in the past few years.
The United States Fish and Wildlife Service and National Marine Fisheries Service have classified hawksbills as endangered under the Endangered Species Actsince 1970. The U.S. government established several recovery plans for protecting E. imbricata.
In 1982 the IUCN Red List of Threatened Species first listed E. imbricata as endangered. This endangered status continued through several reassessments in 1986, 1988, 1990, and 1994 until it was upgraded in status tocritically endangered in 1996. Two petitions challenged its status as an endangered species prior to this, claiming that the turtle (along with three other species) had several significant stable populations worldwide. These petitions were rejected based on their analysis of data submitted by the Marine Turtle Specialist Group (MTSG). The data given by the MTSG showed that the worldwide hawksbill sea turtle population had declined by 80% in the three most recent generations, and that there was no significant population increase as of 1996. CR A2 status was denied however, because the IUCN did not find sufficient data to show the population likely to decrease by a further 80% in the future.
The species (along with the entire family Cheloniidae) has been listed on Appendix I of the Convention on International Trade in Endangered Species. It is illegal to import or export turtle products, or to kill, capture, or harass hawksbill sea turtles.
Local involvement in conservation efforts has also increased in the past few years.
The United States Fish and Wildlife Service and National Marine Fisheries Service have classified hawksbills as endangered under the Endangered Species Actsince 1970. The U.S. government established several recovery plans for protecting E. imbricata.
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