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.
The hawkbill'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-likeappearance 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.
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. 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.
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 een mangrove swamps in estuaries. 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. While they are known to be omnivorous, the principal food of hawkbill turtles are 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. Select sponge species known to be fed on by these turtles include Geodia gibberosa. Aside from sponges, hawksbills also feed on algae and cnidarians like jellyfish and sea anemones. 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 Man o' War's stinging cells cannot penetrate the turtles' armoured heads. 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. Much is not known about the life history of Eretmochelys imbricata. 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. 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. 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 centimetres (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. 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. 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. 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. 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. 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 tribeCarettini 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. The hawksbill turtle was originally described by Carolus Linnaeus as Testudo imbricata in 1766. It was moved into the genus Eretmochelys by the Austrian zoologist Leopold Fitzinger in 1843. In 1857, the species was redescribed as Eretmochelys imbricata squamata, a designation that is now invalid. 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 thePacific Ocean. 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. 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. Caretta is the genus of the hawksbill's much larger relative, the loggerhead turtle. 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. In the U.S. Virgin Islands, Eretmochelys imbricata nests (along with the nests of other sea turtles like Dermochelys coriacea) are often raided bymongooses right after being laid. 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 was no significant increase in the turtles' populations as of 1996. In light of this data, the IUCN applied thecritically endangered (A1) status upon the species. CR A2 status was denied however, because the IUCN believed that there was insufficient data to show that the population of hawksbill turtles were due to decrease by a further 80% in the future. Historically, Eretmochelys imbricata was first listed as endangered by the IUCN in 1982. This endangered status continued all the way through several reassessments in 1986, 1988,1990 and 1994 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. It is illegal to import or export turtle products, kill, capture or harass hawksbill turtles Local involvement in the conservation efforts for the species have 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.Ecology and life history
Habitat
Feeding ecology[edit]Life history
Evolutionary history
Etymology and taxonomic history
Conservation
See also
References
Comments
Post has no comments.