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Hawksbill

Reptiles of Ecuador | Testudines | Cheloniidae | Eretmochelys imbricata

English common names: Hawksbill, Hawksbill Sea Turtle.

Spanish common name: Carey, tortuga carey.

Recognition: ♂♂ 85 cmThis is a measurement of the straight length of the carapace. ♀♀ 114 cmThis is a measurement of the straight length of the carapace.. Members of Eretmochelys imbricata can be separated from other sea turtles by having four pairs of costal shields, two pairs of prefrontals, and overlapping carapace shields. They can also be recognized by their elongated head that ends in a sharp, curvy beak, and their serrated carapace margins, which resemble a saw. Adult males and females are similar in size, but males have a long thick tail and a slightly concave plastron (the ventral part of the shell).

Picture: Adult female. San Cristóbal Island. Galápagos, Ecuador.

Picture: Adult female. San Cristóbal Island. Galápagos, Ecuador.

Picture: Post-hatchling. Parque Nacional Machalilla. Manabí, Ecuador.

Natural history: Uncommon. After hatching on tropical beaches, hatchlings of Eretmochelys imbricata frantically swim for 1–3 days in an offshore direction until they reach open ocean "nursery" habitats^1,2 where they spend 7–10 years² drifting in masses of floating seaweed along with surface currents. Some hatchlings remain on coastal pelagic waters or reefs close to their natal beaches.¹ During this early stage, Hawksbills are diurnal predators of fish and their eggs, tunicates, crabs, barnacles, beetles, algae, and woody plant remains.^1,3 At night, they spend most of their time floating at the surface.⁴ Hawksbill Sea Turtle hatchlings worldwide are preyed upon by a variety of animals, including skunks, raccoons, sea birds, kites, owls, crows, sharks, fish, and crabs.^5–7

When they reach a carapace length of 13–35 cm,^3,4 Hawksbill Sea Turtles establish their home ranges in insular coral reefs, but also on rocky outcrops, banks, lagoons, and mangrove estuaries adjacent to their nesting areas.^8,9 From this age onwards, the young Eretmochelys imbricata become diurnal carnivorous bottom feeders,³ actively foraging among coral crevices in search for sea sponges (which account for 90–95% of their diet),³ but also echinoderms (sea cucumbers and sea urchins), bryozoans, cnidarians (hydrozoans, hard coral, zoanthids, anemones, corallimorphs, jellyfish, and comb jellies), mollusks (squid, snails, nudibranchs, bivalves, and tusk shells), arthropods (crabs, lobsters, barnacles, and copepods), tunicates, fish, algae, sea grass, mangrove fruits and seeds, bark, and wood.^3,4,7,8,10 Presumably as a result of this diet, individuals of E. imbricata are biofluorescent, although part of the fluorescence is likely emitted by algae living on the turtles.¹¹

Hawksbill Sea Turtles spend up to 92% of the day¹² conducting shallow (2–20 m deep) dives,^12,13 although they can dive down to 200 m in depth¹⁴ and for up to 140 minutes.¹⁵ Occasionally, adults bask on shore during daytime.¹⁶ At night, they may also be active,² but are generally sleeping under or wedged into coral or rock ledges⁸ in shallow (7–18 deep) water,¹² surfacing for air every 35–45 minutes.¹⁷ Adults of Eretmochelys imbricata tend to be permanent residents of 75–1,070 km² foraging home ranges¹⁴ in coastal waters within 1 km from shore.¹ However, some individuals migrate. They travel (probably using geomagnetic cues)¹⁸ across open ocean to distant (up to 4,669 km away)¹⁹ rookeries, foraging grounds, or nesting beaches.

In the Galápagos Archipelago, some Hawksbill Sea Turtles reside and breed in the islands, but others migrate to nesting grounds in Central and South America.^20,21 On the coast of mainland Ecuador, some breed and feed locally,^9,22,23 but others also travel to Galápagos and presumably elsewhere along the eastern Pacific.²¹

Hawksbills become sexually mature at an age of 31–38 years.⁶ From this age onwards, they gather in polyandrous (a female copulates with more than one male)⁸ breeding rookeries in shallow waters not necessarily close to the nesting beaches.⁶ Here, copulation takes place on the water surface and may last for 1–3 hours.²⁴ Hybridization between individuals of E. imbricata and other sea turtle species such as Caretta caretta,²⁵ Chelonia mydas,²⁶ and Lepidochelys olivacea,²⁷ occurs. Female Hawksbill Sea Turtles are capable of storing sperm throughout the breeding season,²⁸ and in some populations 6–100% of the resulting clutches are sired by multiple males.^28–30

Hawksbill Sea Turtles nest every 2–9 years⁶ on roughly (less than 3.2 km apart)⁴ the same beaches (which may also be the same on which they themselves hatched),³⁰ but may sometimes select different beaches up to 38 km apart.² In Ecuador, females nest between November and April.^31,32 During a single season, females of Eretmochelys imbricata may lay 1–7 clutches⁶ at intervals of 8–30 days.^4,6 They produce 21–257 eggs per clutch^6,33 and lay them on small isolated beaches⁸ in 17–72 cm deep nests,⁶ usually in the sand under vegetation³⁴ at night.⁸ During nesting emergences, which last 1–2.5 hours,⁸ the females are very shy, and can easily be scared back into the sea.³⁵ Nesting is mostly solitary,⁸ with usually no more than 94 females nesting in a single beach per season.³⁶

The incubation period for Hawksbill eggs is 43–91 days,⁸ and an average of 37–100% of the eggs hatch.⁶ Temperature determines the sex of the offspring,³⁷ and the proportion of female hatchlings increases with the incubation temperature.² In nesting grounds throughout the world, eggs of Eretmochelys imbricata are preyed upon mostly by mammals (including pigs, foxes, dogs, skunks, mongooses, raccoons, coatis, genets, and rats), but also by monitor lizards, crabs, ants, and fly larvae.^2,7,8 They are also occasionally lost to storms, high tides, sand displacement, and disturbance by other nesting turtles, in addition to being widely used for human consumption.^6,8,38 The eggs hatch synchronously and usually at night or late in the afternoon,⁸ but some hatchlings are unable to dig their way out of the nest, and perish.⁸ During nocturnal emergence, the presence of artificial lighting affects the orientation of hatchlings,⁸ which may result in mortality caused by traffic. During diurnal emergence, desiccation causes hatchling mortality.⁸ From the surviving stock, it is estimated that less than 0.1% reach maturity.³⁹

In addition to predation by sharks,⁴⁰ large fish,⁴¹ crocodiles,⁴² and jaguars,⁴³ causes of mortality for adult Hawksbills include hurricanes,²⁴ ingestion of plastic,⁴⁴ collision with boats,²⁴ interactions with fishing gear,⁸ direct harvesting for meat consumption (although their meat may cause food poisoning),⁸ and oil spills.⁴⁵ Individuals of Eretmochelys imbricata are parasitized by a variety of worms,⁴⁶ leeches,⁴⁷ and colonized by crustaceans (including amphipods, crabs, and barnacles), polychaetes, nudibranchs, ascideans, ophiuroids, blue-green bacteria, and algae.^6,8 The maximum estimated lifespan of members of E. imbricata is 55 years.²

Conservation: Critically Endangered.⁴⁸ Eretmochelys imbricata is listed in this category because its populations have declined 84–87% over the past three generations as a result of over-exploitation of adults to provide for the "tortoise shell" industry, direct harvesting of eggs and adults for meat, incidental mortality due to interactions with artisanal and industrial fisheries, and degradation of marine and nesting habitats.⁴⁸ Another threat faced by E. imbricata is climate change. Since temperature during incubation determines the sex of the offspring,³⁷ the increase of the average global temperature may result in the complete feminization of some populations.⁴⁹ Similarly, deforestation in nesting areas also produces a temperature increase that results in a sex ration distortion, where the proportion of females is much higher than males.⁵⁰ Under some scenarios of global sea level rise, up to 50–51% of nesting beach area for E. imbricata may be lost by 2100.^51,52

Distribution: The entire tropical Atlantic, Indian, and Pacific oceans.

Etymology: The generic name Eretmochelys, which comes from the Greek words eretmon (meaning “oar”) and chelys (meaning “turtle”),⁵³ is probably a reference to the paddle-shaped limbs. The specific epithet imbricata, which comes from the Latin word imbricatus (meaning “overlapping”),⁵³ refers to the overlapping carapace shields.

See it in the wild: Individuals of Eretmochelys imbricata can be seen year-round with ~10% certainty in shallow waters throughout Galápagos, especially near Puerto Baquerizo Moreno. Swimming Hawksbills can occasionally be observed from boats going to and from tourism sites, but they are easier to spot while snorkeling or diving in coral reefs. Along the coast of mainland Ecuador, E. imbricata is harder to see. Although the species nests roughly on the same beaches during the same months, witnessing such events is rare. Swimming Hawksbills can occasionally be observed while navigating on motorized boats off the coast of Machalilla National Park.

Authors: Alejandro Arteaga^aAffiliation: Khamai Foundation, Quito, Ecuador. and Juan M Guayasamin^bAffiliation: Laboratorio de Biología Evolutiva, Universidad San Francisco de Quito (USFQ), Quito, Ecuador.^,cAffiliation: Galapagos Science Center, Galápagos, Ecuador.^,dAffiliation: Centro de Investigación de la Biodiversidad y Cambio Climático, Universidad Tecnológica Indoamérica, Quito, Ecuador.

Academic reviewers: Juan José Alava.

Photographers: Jose Vieira^aAffiliation: Tropical Herping (TH), Quito, Ecuador.^,eAffiliation: ExSitu, Quito, Ecuador. and Alejandro Arteaga^aAffiliation: Tropical Herping (TH), Quito, Ecuador.

How to cite? Arteaga A, Guayasamin Jm (2020) Eretmochelys imbricata. In: Arteaga A, Bustamante L, Vieira J (Eds) Reptiles of Ecuador: Life in the middle of the world. Available from: www.reptilesofecuador.com

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