The Hawksbill Sea Turtle (Eretmochelys imbricata) is a critically endangered sea turtle belonging to the family Cheloniidae. It is the only extant species in its genus. The species has a worldwide distribution, with Atlantic and Pacific 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.
Anatomy and morphologyEdit
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.
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.
Hawksbill sea turtles' sand tracks are asymmetrical, because they crawl on land with an alternating gait. By contrast, the green sea turtle and the leatherback turtle crawl rather symmetrically. 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.
Due to its consumption of venomous cnidarians, hawksbill sea turtle flesh can become toxic.
In the Caribbean, the main nesting beaches are in Antigua and Barbuda, Barbados, Guadeloupe, Puerto Rico (Mona Island),Tortuguero in Costa Rica and in the Yucatan. They feed in the waters off Cuba and around Mona Island near Puerto Rico among other places.In the Atlantic, E. imbricata populations range as far west as the Gulf of Mexico and as far southeast as the Cape of Good Hope in South Africa. They live off the Brazilian coast (specifically Bahia) through southern Florida and the waters off Virginia. The species' range extends as far north as the Long Island Sound and Massachusetts in the west Atlantic and the frigid waters of the English Channel in the east (the species' northernmost sighting to date).
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.
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. 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.
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 of siliceous spicules, such as Ancorina, Geodia, Ecionemia, and Placospongia.
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 the Seychelles 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. imbricatanormally 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 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. imbricatajuveniles reach around 35 centimeters (14 in) they switch from a pelagic life style to living on coral reefs.
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 highly migratory. Because of their tough carapaces, adults' only predators are sharks, estuarine crocodiles, octopuses, and some species of pelagic fish.
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 to critically 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. 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.
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 Act since 1970. The U.S. government established several recovery plans for protecting E. imbricata.