Hawksbill sea turtle
The hawksbill sea turtle 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 global distribution that is largely limited to tropical and subtropical marine and estuary ecosystems.
The appearance of the hawksbill is similar to that of other sea turtles. In general, it has a flattened body shape, a protective carapace, and flipper-like limbs, 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. The World Conservation Union classifies E. imbricata as critically endangered, primarily as a result of human fishing practices. Hawksbill shells were the primary source of tortoiseshell material used for decorative purposes. The Convention on International Trade in Endangered Species regulates the international trade of hawksbill sea turtles and products derived from them.
Taxonomy
Linnaeus 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 the genus Eretmochelys. In 1857, the species was temporarily misdescribed as Eretmochelys imbricata squamata.Neither the IUCN nor the United States Endangered Species Act assessment processes recognize any formal subspecies, but instead recognize one globally distributed species with populations, subpopulations, or regional management units.
Fitzinger derived the genus name Eretmochelys from the Ancient Greek roots eretmo and chelys, corresponding to "oar" and "turtle", respectively, in reference to the turtles' oar-like front flippers. The species name imbricata is Latin, corresponding to the English term imbricate, in reference to the turtles' shingle-like, overlapping carapace scutes.
Description
Adult hawksbill sea turtles typically grow to in length, weighing around on average. The heaviest hawksbill ever captured weighed. 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 forelimbs have two visible claws on each flipper.
A readily distinguished characteristic of the hawksbill 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 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 can reach almost in length. The hawksbill appears to frequently employ its sturdy shell to insert its body into tight spaces in reefs.
Crawling with an alternating gait, hawksbill tracks left in the sand are asymmetrical. In contrast, the green sea turtle and the leatherback turtle have a more symmetrical gait.
Due to its consumption of venomous cnidarians, hawksbill sea turtle flesh can become toxic.
The hawksbill is biofluorescent and is the first reptile recorded with this characteristic. If the effect is due to the turtle's diet, which includes biofluorescent organisms like the hard coral Physogyra lichtensteini, is unknown. Males have more intense pigmentation than females, and a behavioral role of these differences is speculated.
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. Two significant subpopulations are known, in the Atlantic and Indo-Pacific.Atlantic subpopulation
In the Atlantic, hawksbill 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.Along the East Coast of the United States, hawksbill sea turtles range from Virginia to Florida. In Florida, according to the Florida Fish and Wildlife Conservation Commission, hawksbills are found primarily on reefs in the Florida Keys and along the southeastern Atlantic coast. Several major nesting sites are found in coastal Palm Beach, Broward, and Dade Counties. THE FLORIDA HAWKSBILL PROJECT, is a comprehensive research and conservation Program to study and protect the region's hawksbill sea turtles and the habitats in which they live. Within the scope of this project, numerous studies have been undertaken to characterize the hawksbill aggregations found in southeast Florida waters, and educational programs have been developed to engage the local dive community in the protection of hawksbill sea turtles and coral reef habitats. This program is hosted by the National Save the Sea Turtle Foundation, located in Fort Lauderdale, Florida. Throughout their global range, hawksbill turtles are known to closely associate with coral reef habitats, mostly due to their preference for eating sponges and corals. Due to the large extent of Florida's barrier reefs, the Hawksbill Project focuses on representative sites in the northern, central, and southern sections of the Southeast Florida Reef Tract. The barrier reefs of northern Palm Beach County, the patch reefs of the northern Keys, and the finger reefs of Key West are the primary locations for their sampling efforts
In the Caribbean, the main nesting beaches are in the Lesser Antilles, Barbados, Guadeloupe, Tortuguero in Costa Rica, and the Yucatan. They feed in the waters off Cuba and around Mona Island near Puerto Rico, among other places.
Indo-Pacific subpopulation
In the Indian Ocean, hawksbills are a common sight along the east coast of Africa. One can find them in the seas surrounding Madagascar and Mozambique, and island groups such as Primeiras e Segundas, which include the turtle protection island of Ilha do Fogo. Hawksbills are also common along the southern Asian coast, including the Persian Gulf, the Red Sea, and the Indian subcontinental and Southeast Asian coasts. They are present across the Malay Archipelago and northern Australia. Their Pacific range is limited to the ocean's tropical and subtropical regions. In the west, it extends from the southwestern tips of the Korean Peninsula and the Japanese Archipelago south to northern New Zealand.The Philippines hosts several nesting sites, including the island of Boracay and Punta Dumalag in Davao City. Dahican Beach in Mati City, Davao Oriental, hosts one of the essential hatcheries of its kind, along with olive ridley sea turtles in the archipelagic country of the Philippines. A small group of islands in the southwest of the archipelago is named the "Turtle Islands" because two species of sea turtles nest there: the hawksbill and the green sea turtle. In January 2016, a juvenile was seen in Gulf of Thailand. A 2018 article by The Straits Times reported that around 120 hawksbill juvenile turtles recently hatched at Pulau Satumu, Singapore. Commonly found in Singapore waters, hawksbill turtles have returned to areas such East Coast Park and Palau Satumu to nest. In Hawaii, hawksbills mostly nest on the "main" islands of Oahu, Maui, Molokai, and Hawaii. In Australia, hawksbills are known to nest on Milman Island in the Great Barrier Reef. Hawksbill sea turtles nest as far west as Cousine Island in the Seychelles, where the species since 1994 is legally protected, and the population is showing some recovery. The Seychelles' inner islands and islets, such as Aldabra, are popular feeding grounds for immature hawksbills.
Eastern Pacific subpopulation
In the eastern Pacific, hawksbills are known to occur from the Baja Peninsula in Mexico, south along the coast to southern Peru. Nonetheless, as recently as 2007, the species had been considered extirpated mainly in the region. Important remnant nesting and foraging sites have since been discovered in Mexico, El Salvador, Nicaragua, and Ecuador, providing new research and conservation opportunities. In contrast to their traditional roles in other parts of the world, where hawksbills primarily inhabit coral reefs and rocky substrate areas, in the eastern Pacific, hawksbills tend to forage and nest principally in mangrove estuaries, such as those present in the Bahia de Jiquilisco, Gulf of Fonseca, Estero Padre Ramos, and the Gulf of Guayaquil. Multi-national initiatives, such as the , are currently pushing efforts to research and conserve the population, which remains poorly understood.Habitat and feeding
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. However, they have been known to seek habitats where they are able to camouflage or hide to minimize predator detection.Feeding
While they are omnivorous, sea sponges are their principal food; they constitute 70–95% of the turtles' diets. 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, marine plants, woody plant remains, mangrove fruits and seeds, cnidarians, comb jellies, bryozoans, mollusks, echinoderms, tunicates, fish and their eggs, crustaceans, and arthropods. 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.