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Aug 03, 2014 Features / Columnists, Interesting Creatures in Guyana
The hawksbill sea turtle (Eretmochelys imbricata) is a critically endangered sea turtle belonging to the family Cheloniidae. It is the only extant species in the genus Eretmochelys. The species has a worldwide distribution, with Atlantic and Indo-Pacific subspecies—E. i. imbricata and E. i. bissa, respectively.
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. It 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 colours, 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 were 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.
They have 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 one metre (3 ft) in length, weighing around 80 kg (180 lb) on average. The heaviest hawksbill ever captured was measured to be 127 kg (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 colours radiating to the sides.
Several characteristics of the hawksbill sea turtle 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, its 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. 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.
Due to its consumption of venomous cnidarians, hawksbill sea turtle flesh can become toxic.
Hawksbill sea turtles have a wide range, found predominantly in tropical reefs of the Indian, Pacific, and Atlantic Oceans. Of all the sea turtle species, this one is most associated with warm tropical waters. Two major subpopulations are acknowledged to exist, the Atlantic and Indo-Pacific subpopulations.
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. Little is known about the habitat preferences of early life-stage. And so like other sea turtle young, it is assumed to be completely pelagic, remaining at sea until maturity.
While they are omnivorous, sea sponges are the principal food of hawksbill sea turtles. Sponges constitute 70–95 per cent of their diets in the Caribbean. However, like many spongivores, they feed only on select species, ignoring many others.
Caribbean populations feed primarily on the orders Astrophorida, Spirophorida, and Hadromerida in the class Demospongiae. Aside from sponges, hawksbills feed on algae, cnidarians, comb jellies and other jellyfish, and sea anemones. They also 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. The man o’ war’s stinging cells cannot penetrate the turtles’ armoured heads.
Hawksbills are highly resilient and resistant to their prey. Some of the sponges they eat, are highly (often lethally) toxic to other organisms.
Not much is known about the life history of hawksbills. Their life history can be divided into three phases, namely the pelagic phase, from hatching to about 20 cm, the benthic phase, when the immature turtles recruit to foraging areas, and the reproductive phase, when they reach sexual maturity. The pelagic phase possibly lasts one to four years. Hawksbills show a degree of fidelity after recruiting to the benthic phase, however movement to other similar habitats is possible.
(Source: Wikipedia – The Free Online Encyclopedia)
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