Hawksbill sea turtle

Appearance

Adult hawksbill sea turtles typically grow to 1 m in length, weighing around 80 kg on average. The heaviest hawksbill ever captured weighed 127 kg.

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.

Several characteristics of the hawksbill sea turtle distinguish it from other sea turtle species. Its elongated, tapered head ends in a beak-like mouth, and its beak is more sharply pronounced and hooked than others. The hawksbill's fore limbs 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. imbricatas 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 hawksbill sea turtle has been shown to be biofluorescent and is the first reptile recorded with this characteristic. It is unknown if this is derived from the turtle's diet, which includes biofluorescent organisms like the hard coral "Physogyra lichtensteini". Males have more intense pigmentation than females, and a behavioural role of these differences is speculated.

Naming

Linnaeus originally described the hawksbill sea turtle as "Testudo imbricata" in 1766, in the 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".

Two subspecies are accepted in "E. imbricata's" taxon. "E. i. bissa" refers to populations that reside in the Pacific Ocean. The Atlantic population is a separate subspecies, "E. i. imbricata". 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.

Distribution

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, "E. imbricata" is the one most associated with warm tropical waters.

Status

Consensus has determined sea turtles, including "E. imbricata" to be, at the very least, threatened species because of their slow growth and maturity, and slow reproductive rates. Many adult turtles have been killed by humans, both accidentally and deliberately. Their existence is threatened due to pollution and loss of nesting areas because of coastal development. Human and animal encroachment threatens nesting sites, and small mammals dig up the eggs to eat. In the US Virgin Islands, mongooses raid hawksbill nests right after they are laid.

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.

Little is known about the habitat preferences of early life-stage "E. imbricata"; like other young sea turtles, they are assumed to be completely pelagic, remaining at sea until they mature.

Reproduction

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, then lay clutches of eggs and cover them with sand. Caribbean and Florida nests of "E. imbricata" normally contain around 140 eggs. After the hours-long process, the female returns to the sea.

The baby turtles, usually weighing less than 24 g hatch at night after around two months. These newly emergent hatchlings are dark-colored, with heart-shaped carapaces measuring around 2.5 cm long. They instinctively crawl into the sea, attracted by the reflection of the moon on the water. 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.

Food

While the hawksbill sea turtles mainly feed on sponges found on coral reefs, they also feed on crustaceans, algae, and fish. They are prey to large fish, sharks, and humans. The hawksbill sea turtles are unfortunately endangered mainly due to human impact. These sea turtles mainly stay close to shorelines as this is where sponge-bearing coral reefs can be found, as well as beaches that provide nesting sites.

While they are omnivorous, sea sponges are their principal food; they constitute 70–95% of the turtles' 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. Hawksbills close their unprotected eyes when they feed on these cnidarians. The man o' war's stinging cells cannot penetrate the turtles' armored heads.

Hawksbills are highly resilient and resistant to their prey. Some of the sponges they eat, such as "Aaptos aaptos", "Chondrilla nucula", "Tethya actinia", "Spheciospongia vesparium", and "Suberites domuncula", are highly toxic to other organisms. In addition, hawksbills choose sponge species with significant numbers of siliceous spicules, such as "Ancorina", "Geodia", "Ecionemia", and "Placospongia".