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Hawksbill Sea Turtle

Eretmochelys imbricata (Linnaeus 1766)

Lifespan, longevity, and ageing

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Observations: These animals have been kept in captivity for more than 20 years. Their longevity in the wild is unknown (http://www.pwrc.usgs.gov/neparc/).
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Behavior

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The mechanisms that aid hawksbill turtles in returning to their nesting beaches are still unknown. It has been thought that these turtles are guided inland by magnetic fields and lunar phases/position.

This species communicates by the use of ritual mating behaviors.

Communication Channels: visual ; tactile

Perception Channels: visual ; tactile ; acoustic ; chemical ; magnetic

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Conservation Status

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It is very difficult to classify how endangered hawksbill turtles are because they are found throughout the world and are migratory. In some places, they may be very scarce, and in others they may thrive. Also, since there is little knowledge of their early population levels, it is very hard to know how much the populations have declined.

Currently (throughout the world), it is illegal to trade hawksbill turtle products. This should create the expansion of the turtles because their major predator, humans, will no longer be able to hunt them. In order to succeed in keeping hawksbill turtles in existence, there must be cooperation among all nations that have hawksbill populations in their waters. Free exchange of information on the turtles is needed to ensure that all nations are aware of the best and most efficient ways of keeping hawksbill turtles in existence.

US Federal List: endangered

CITES: appendix i

IUCN Red List of Threatened Species: critically endangered

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Life Cycle

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Hawksbill turtles hatch out of eggs. As a hawksbill turtle matures, its carapace shifts from heart-shaped to more elongate. Sex determination is thought to be temperature-dependent as is the case with other sea turtles and reptiles, however not enough data is available to be sure this is true.

Development - Life Cycle: temperature sex determination

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Benefits

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There are no known adverse affects of Eretmochelys imbricata imbricata on humans.

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Benefits

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For years, humans have hunted the hawksbill turtles in order to sell their scutes. Also, humans eat the turtles as well as their eggs.

Positive Impacts: food ; body parts are source of valuable material

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Associations

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Hawksbill turtles often times feed on sponges, causing succession to occur in the reef and freeing up space for settlement of other organisms.

Ecosystem Impact: creates habitat

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Trophic Strategy

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Hawksbill turtles feed primarily on sponges. They show a large level of feeding selectivity in the way that they only eat certain species of sponges, some of which are toxic to other animals. Sea jellies and other coelenterates are also common prey items. These turtles are omnivorous and also eat mollusks, fish, marine algae, crustaceans, and other sea plants and animals. A preferred feeding ground of the turtles is in shallow shoals abundant with brown algae.

Animal Foods: fish; mollusks; aquatic or marine worms; aquatic crustaceans; echinoderms; cnidarians; other marine invertebrates

Plant Foods: leaves; wood, bark, or stems; fruit; algae; macroalgae

Primary Diet: omnivore

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Distribution

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Eretmochelys imbricata imbricata are found mainly in the tropical regions of the Atlantic and Pacific oceans. However, in the western hemisphere, they have been reported to have nests as far north as Woods Hole, Massachusetts. They are also present in the Long Island Sound. However, between the Carolinas and New Jersey, very few hawksbill turtles have been recorded.

Biogeographic Regions: australian ; oceanic islands ; indian ocean; atlantic ocean ; pacific ocean ; mediterranean sea

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Habitat

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Hawksbill turtles are most commonly found in hard-bottomed and reef habitats containing sponges. They also reside in shoals, lagoons of oceanic islands, and continental shelves. In general, they are found in water no deeper than sixty feet (18.3 m). When hawksbill turtles are young, the are unable to dive into deep water, and therefore are forced to live in masses of floating sea plants, such as sargassum.

Range depth: 20 to 0 m.

Average depth: Near Surface m.

Habitat Regions: saltwater or marine

Aquatic Biomes: reef

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Life Expectancy

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The normal lifespan of hawksbill turtles is thought to be about 30 to 50 years, however biologists are not sure exactly how long they live.

Range lifespan
Status: captivity:
20+ (high) years.

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Morphology

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Young hawksbill turtles have a heart-shaped carapace. As these turtles mature, their carapaces becomes more elongated. In all of the hawksbill turtles, with the exception of very old individuals, the lateral and posterior areas of the carapace are serrated. The heads of hawksbill turtles taper into a V shape, giving them the appearance of birds' beaks.

Eretmochelys imbricata imbricata have 5 features that distinguish them from other sea turtles. Their heads have two pairs of prefrontal scales. They also have two claws on each of their forelimbs. There are thick, overlapping scutes on their carapaces, which also have four pairs of costal scutes. Their elongate mouths resemble a beak, that taper off to a sharp point at the end.

Hawksbill turtles are relatively small sea turtles. Nesting females average a length of 87 centimeters in curved carapace length and weigh 80 kilograms. The average hatchling Eretmochelys imbricata imbricata in the parts of the Caribbean owned by the United States is about 42 millimeters in straight carapace length and weighs 13.5 to 19.5 grams. Male turtles are distinguished by a brighter pigmentation, a concave plastron, long claws, and a thicker tail.

Range mass: 35.7 to 127 kg.

Average mass: 80 kg.

Range length: 62.5 to 114 cm.

Average length: 87 cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: male more colorful; sexes shaped differently

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Associations

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Hawksbill turtles, like all turtles, have a hard shell that discourages predators from trying to eat them. Adult turtles are still consumed by humans, sharks, crocodiles, large fish, and octopi. Nests are commonly robbed by terrestrial predators such as dogs, raccoons, rats, and humans.

Directly after hatching, hawksbill turtles face the most dangerous time of their lives: the journey to water. Although this scramble only lasts a few minutes, countless hatchlings are preyed on by flocks of gulls and large crabs.

Known Predators:

  • humans (Homo sapiens)
  • domestic dogs (Canis lupus familiaris)
  • raccoons (Procyon lotor)
  • rats (Rattus)
  • gulls (Larus)
  • ghost crabs (Ocypode)
  • tiger sharks (Galeocerdo cuvier)
  • requiem sharks (Carcharhinus)
  • groupers (Epinephelus)
  • estuarine crocodiles (Crocodylus porosus)
  • common octopus (Octopus vulgaris)
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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Reproduction

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Mating occurs roughly every 2 to 3 years. It occurs mainly in shallow waters. No information is available as to whether or not these turtles have life-long partners or are promiscuous.

Copulation usually begins in shallow water near the shore. Males lie and wait in the shallow water for the females to return. At times, males have been seen following the females on shore. However, this behavior is rarely observed.

The entire nesting process takes roughly one to three hours. It involves similar steps as most other species of sea turtles. The turtles come out of the sea and select a site in which to lay their eggs. They then clear the area and dig a pit in the sand. Next they lay their eggs and then proceed to fill in the pit in with their hind limbs. After the site is disguised, the turtles return to the sea.

Breeding interval: The females lay three clutches a year at an interval of roughly thirteen to fifteen days.

Breeding season: Nesting generally occurs between July and October.

Average number of offspring: 140.

Average gestation period: 60 days.

Average age at sexual or reproductive maturity (female): 3 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous

Average age at sexual or reproductive maturity (male)
Sex: male:
1277 days.

Average age at sexual or reproductive maturity (female)
Sex: female:
1277 days.

After laying the eggs on the beach, the females retreat into the water. After about 60 days, the eggs hatch, and the newborn turtles make a perilous dash for the water where they will mature.

Parental Investment: no parental involvement

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Edelman, M. 2004. "Eretmochelys imbricata" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eretmochelys_imbricata.html
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Michael Edelman, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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Matthew Wund, University of Michigan-Ann Arbor
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Biology

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Hawksbills may take decades to mature and it could be between 20 to 40 years before they are ready to breed (10). Upon reaching sexual maturity, a female will typically lay up to five clutches of around 100 to 140 eggs in one breeding season, and then wait a few years before nesting again (6). Nesting is much more dispersed than in other marine turtles, but individuals do tend to return to a particular beach season after season (10). Having survived the dash to the sea, hatchlings are believed to spend their first few years in the open ocean before returning to more sheltered coastal waters. Recent studies indicate that the oceanic phase may be shorter for hawksbills, or even omitted in certain regions, as hatchlings swim less vigorously than those of other species (7). Probably less than one out of 1000 eggs will survive and reach adulthood (10). Adults are opportunistic predators, using their sharp beak to prize invertebrate prey from crevices within the reef. Unusually amongst marine animals (to whom they are often unpalatable), sponges make up the majority of the hawksbill's diet (6).
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Conservation

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International trade in the hawksbill turtle is banned amongst signatory nations by its listing on Appendix I of the Convention on International Trade in Endangered Species (CITES) (3), but extensive illegal trafficking still occurs between CITES signatories and among other nations. Preventing this black market trade is the key to saving this species and TRAFFIC (the wildlife trade monitoring arm of WWF and IUCN-World Conservation Union) is involved in monitoring and highlighting this problem (13). In 1988, the government of the Seychelles took a very public stand against tortoiseshell trade by burning a stockpile of seized shells (4), in a manner reminiscent of burning ivory pyres in Kenya. Action to save the world's turtles is being taken by many international bodies and recent increases in hawksbill nesting populations have been observed at a few well-protected sites (10). With successful monitoring of populations and a decrease in illegal trade, the hawksbill may respond well to long-term protection.
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Description

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This Critically Endangered marine turtle has been exploited for thousands of years as the sole source of commercial tortoiseshell. The beautiful carapace is generally streaked and marbled with amber, yellow or brown and often has a strongly serrated edge (5). Unlike other species, the scales (or scutes) of the carapace overlap. The narrow head and strongly hooked beak give rise to this turtle's common name (6), while the imbricate nature of the (overlapping) scutes give rise to the Latin species name of 'imbricata' (7).
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Habitat

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Adult hawksbill turtles are mainly associated with the clear, relatively shallow water of coastal reefs, bays, estuaries and lagoons, with nesting generally occurring on remote, isolated sandy beaches (6) (9).
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Range

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Hawksbill turtles are found throughout the world in tropical waters and are known to nest on beaches in at least 60 countries (8). Recent evidence indicates that hawksbills take part in long distance migrations with breeding and feeding grounds in very different locations (5), although they tend to be more sedentary (move less) than other sea turtles species.
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Status

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Classified as Critically Endangered (CR) on the ICUN Red List 2007 (1). Listed on Appendix I of CITES (3), and Appendix I of the Convention on Migratory Species (CMS or Bonn Convention) (4).
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Threats

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Global numbers are very difficult to estimate but it appears that this turtle has suffered drastic decline, probably by as much as 80 percent over the last century (1) (8). Major threats to survival come from illegal trade in the turtle's prized shell, known as tortoiseshell, which has been sought for jewellery and ornaments for centuries. There is also a substantial market for eggs, meat and even stuffed juveniles as exotic gifts in some parts of the world (11). Additional pressure on the global population comes from harvests to support traditional customs, the loss of nesting sites, accidental entanglement in fishing lines and the deterioration of coral reef systems which act as feeding sites for these turtles (12).
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Behaviour

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Carnivorous, feeding largely on sessile marine invertebrates, such as sponges and soft corals.

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Conservation Status

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Critically Endangered

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Description

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A moderately sized marine turtle; largest Egyptian specimen has a carapace length of 835 mm. Carapace depressed, elongate, smooth; scutes imbricate in younger animals, increasingly less so in older specimens; posterior edge strongly serrate; 4 cosatal scutes; first marginal scute in contact with first vertebral scute. Head rather small, narrow, with two pairs of prefrontals. Snout is beak-like, elongate. There area 2 claws on each limb. Males smaller, with longer tails and larger claws. Color of carapace yellowish brown, with dark brown and black radiating streaks; dorsal sides of limbs and head brown, scales edged yellowish. All ventral sides yellowish white.

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Distribution in Egypt

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The Red Sea, where it is the commonest marine turtle; not recorded yet from the Egyptian Mediterranean, although Werner (1988) lists the species from Israeli Mediterranean waters. It has been recorded throughout the Red Sea and in both the Gulfs of Aqaba and Suez. Breeding has been recorded throughout the Hurghada Archipelago, Ras Mohamed, Wadi El Gemal Island, Qulan Islands, Ras Banas, and Zabargad Island.

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Global Distribution

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A pan-tropical species, recorded erratically in the Mediterranean, but not known to breed there.

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Habitat

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Warm tropical and subtropical marine waters, usually near coral reefs and rocky outcrops in shallow waters.

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Status in Egypt

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 Fairly common, but declining. The increase in tourist activities and artisanal fishing in the Red Sea is leading to growing disturbance to the nesting sites of these animals on offshore islands. Development on the mainland is reducing avail­able nesting sites. In the past stuffed animals were commonly offered to tourists, but this has subsided to a large extent.

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Eretmochelys Imbricate is Considered One of the most Endangered Sea Turtles

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The hawksbill is a medium, sized sea turtle often considered the most beautiful of all sea turtles because of the amber scutes on the carapace that are usually streaked with red-brown, black and yellow. Additional distinctive characters include overlapping capace scutes, except in very old individuals. One of smaller sea turtles with adult shell length usually 76-89 cm. Adults usually weigh between 43 and 75 kg (100-165) but may grow as large as 127 kg. Frequent warm, shallow water habitats (less than 20 m) such as bays, shoals, coral reefs, and island (nesting), females lay several hundered eggs on exposed sand beach every 2 to 3 years. Turtle has a unique characteristic that is strong homing instict or strong memory and ability as bioindikator to know an area is polluted. With a strong memory, turtles will return to shore where they were first born to spawn and hawksbill turtle have a sharp beak and tapered with a large jaw like beak of eagle and overlapping scales. Adults travel hundereds or thousand of kilometers from foraging grounds to breeding areas and neonates are broadly dispersed by ocean currents. Studies of hawksbill habitat use and behaviour on foraging grounds may also elucidate ecological roles and susceptibility to threats (Leon and Bjorndal, 2002) Although this species has been harvested for meat and eggs, the primary reasons for the decline was harvest for "tortoise shell". As recently as 1991, Japan allowed importation of up to 20 tons of hawksbill turtle shell for their industry. However, recent pressure has caused the japanese government to begin phasis out this industry. A recent trend to offer stuffed juvenile hawksbills as tourist curios continues to be a threat. Because this species tends to nest on small, isolated islands, loss of nesting habitat to development has not been as much of a threat as it has been with other sea turtles. Loss of coral reefs in tropical regions has had a serious effect because of loss of feeding areas. Erosion of barrier island and other actors which decrease available seagrass beds have been a factor in its decline.
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Niger Coastal Delta Habitat

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The Niger Coastal Delta is an enormous classic distributary system located in West Africa, which stretches more than 300 kilometres wide and serves to capture most of the heavy silt load carried by the Niger River. The peak discharge at the mouth is around 21,800 cubic metres per second in mid-October. The Niger Delta coastal region is arguably the wettest place in Africa with an annual rainfall of over 4000 millimetres. Vertebrate species richness is relatively high in the Niger Delta, although vertebrate endemism is quite low. The Niger Delta swamp forests occupy the entire upper coastal delta. Historically the most important timber species of the inner delta was the Abura (Fleroya ledermannii), a Vulnerable swamp-loving West African tree, which has been reduced below populations viable for timber harvesting in the Niger Delta due to recent over-harvesting of this species as well as general habitat destruction of the delta due to the expanding human population here. Other plants prominent in the inner delta flood forest are: the Azobe tree (Lophira alata), the Okhuen tree (Ricinodendron heudelotii ), the Bitter Bark Tree (Sacoglottis gabonensis), the Rough-barked Flat-top Tree (Albizia adianthifolia), and Pycnanthus angolensis. Also present in its native range is the African Oil Palm (Elaeis guineensis)

Five threatened marine turtle species are found in the mangroves of the lower coastal delta: Leatherback Sea Turtle (Dermochelys coricea, EN), Loggerhead Sea Turtle (Caretta caretta, EN), Olive Ridley Turtle (Lepidochelys olivacea, EN), Hawksbill Sea Turtle (Eretmochelys imbricata, CR), and Green Turtle (Chelonia mydas, EN).

There are a number of notable mammals present in the upper (or inner) coastal delta in addition to the Critically Endangered Niger Delta Red Colubus (Procolobus pennantii ssp. epieni), which primate is endemic to the Niger Delta. The near-endemic White-cheeked Guenon (Cercopithecus erythrogaster, VU) is found in the inner delta. The Endangered Chimpanzee (Pan troglodytes) is also found in the inner delta. The limited range Black Duiker (Cephalophus niger) is fournd in the inner delta and is a near-endemic to the Niger River Basin. The restricted distribution Mona Monkey (Cercopithecus mona), a primate often associated with rivers, is found here in the Niger Delta. The Near Threatened Olive Colobus (Procolobus verus) is restricted to coastal forests of West Africa and is found here in the upper delta.

Some of the reptiles found in the upper Coastal Niger Delta are the African Banded Snake (Chamaelycus fasciatus); the West African Dwarf Crocodile (Osteolaemus tetraspis, VU); the African Slender-snouted Crocodile (Mecistops cataphractus); the Benin Agama (Agama gracilimembris); the Owen's Chameleon (Chamaeleo oweni); the limited range Marsh Snake (Natriciteres fuliginoides); the rather widely distributed Black-line Green Snake (Hapsidophrys lineatus); Cross's Beaked Snake (Rhinotyphlops crossii), an endemic to the Niger Basin as a whole; Morquard's File Snake (Mehelya guirali); the Dull Purple-glossed Snake (Amblyodipsas unicolor); the Rhinoceros Viper (Bitis nasicornis). In addition several of the reptiles found in the outer delta are found within this inner delta area.

Other reptiles found in the outer (southernmost) NIger Coastal Delta are the Nile Crocodile (Crocodylus niloticus), African Softshell Turtle (Trionyx triunguis), African Rock Python (Python sebae), Boomslang Snake (Dispholidus typus), Cabinda Lidless Skink (Panaspis cabindae), Neon Blue Tailed Tree Lizard (Holaspis guentheri), Fischer's Dwarf Gecko (Lygodactylus fischeri), Richardson's Leaf-Toed Gecko (Hemidactylus richardsonii), Spotted Night Adder (Causus maculatus), Tholloni's African Water Snake (Grayia tholloni), Smith's African Water Snake (Grayia smythii), Small-eyed File Snake (Mehelya stenophthalmus), Western Forest File Snake (Mehelya poensis), Western Crowned Snake (Meizodon coronatus), Western Green Snake (Philothamnus irregularis), Variable Green Snake (Philothamnus heterodermus), Slender Burrowing Asp (Atractaspis aterrima), Forest Cobra (Naja melanoleuca), Rough-scaled Bush Viper (Atheris squamigera), and Nile Monitor (Varanus niloticus).

There are a limited number of amphibians in the inner coastal delta including the Marble-legged Frog (Hylarana galamensis). At the extreme eastern edge of the upper delta is a part of the lower Niger and Cross River watersheds that drains the Cross-Sanaka Bioko coastal forests, where the near endemic anuran Cameroon Slippery Frog (Conraua robusta) occurs.

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Diagnostic Description

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Carapace in adults cardiform or elliptical, with imbricated dorsal scutes, its width 70 to 79% of its total length (mean 74.1% SCL). Head medium-sized, narrow, with a pointed beak, its length 21 to 33% of the straight carapace length (mean 27.6% SCL); 2 pairs of prefrontal and 3 or 4 postorbital scales; tomium not serrated on the cutting edge, but hooked at the tip. The narrow and elongated snout and the thick scutes of the carapace are adaptations to cope with waves and to obtain food from between corals and rocky substrates.

The scutes are most strongly imbricated at maturity, but in older animals the overlapping character is frequently lost. The scutelation of the carapace is similar to that of Chelonia, with 5 costal, 4 pairs of lateral (the first not touching the precentral scute), 11 pairs of marginal plus one pair of postcentral or pigal scutes. The plastron is covered by 5 pairs of scutes, plus one or two intergular and sometimes one small interanal. There are 4 poreless inframarginal scutes covering each bridge.

Each rear and fore flipper bears 2 claws on its anterior border. As in other species of sea turtles, males have stronger and more curved claws and longer tails than females. Hatchlings and juveniles have a wider carapace than adults, the mean carapace width usually exceeding 76% of its length.They also have three keels of spines along the carapace which disappear with growth. Young adults sometimes have a remnant of the dorsal central keel, without spines. In juveniles and subadults, the scutes of the carapace are indented on the rear third of the carapace margin.

Colour: this species is the most colourful among sea turtles. The pattern shows a large range of variation, from very bright colours to the heavy melanistic forms in the Eastern Pacific. The scales of the head have creamy or yellow margins, more apparent at the sides or cheeks than on the roof. The colour of the thick, horny scutes of the carapace is important in relation to the quality of the "carey" which is determined by its degree of transparency, the intensity of the amber ground colour and the quantity and arrangement, in spots or stripes, of the complementary colours: brown, red, black and yellow. The colour spots and stripes are usually arranged in a fan-like pattern. Underneath, the scutes are rather thin and amber-coloured, in juveniles there are brown spots in the rear part of each scute. The dorsal sides of head and flippers are darker and less variable; in the eastern Pacific population, the coloration is sometimes nearly black- Hatchlings are more homogeneous in colour, mostly brown, with paler blotches on the scutes of the rear part of the carapace, and also small pale spots on the "tip" of each scute along the 2 keels of the plastron.

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FAO species catalogue. Vol.11: Sea turtles of the world. An annotated and illustrated catalogue of sea turtlespecies known to date.Márquez M., R. FAO Fisheries Synopsis.  No. 125, Vol. 11. Rome, 1990 FAO. 81 p.
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Distribution

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Eretmochelys is the most tropical of all sea turtles. It is distributed throughout the central Atlantic and Indo-Pacific regions . The population density is lower than that of Lepidochelys olivacea; also nesting is performed in a more widespread pattern, with very few major nesting places. The hawksbill is more common where reef formations are present; it is also observed in shallow waters with seagrass or algal meadows, including coastal lagoons and bays. Nesting is confined between the 25° N and 35°S, mostly within the tropical region, with very few isolated records outside these latitudes. There are some records of non-nesting turtles outside the abovementioned range, e.g. in the northern hemisphere: western Atlantic, up to Cape Cod, USA; eastern Atlantic, the English Channel; western Pacific, China, up to the Yellow Sea, Shangtung region, and southern Japan - Archipelago of Ryukyu; eastern Pacific to Cedros Island, Baja California, Mexico. In the southern hemisphere: western Atlantic, up to southern Brazil, but no data from Uruguay; eastern Atlantic, often observed in northern Namibia, but sporadically down to the west coast of South Africa; Western Indian Ocean, Red Sea as the northernmost record (nesting ground) and South Africa (Natal) as the southern most record; south-central Pacific, up to New Zealand; eastern Pacific, up to southern Peru, no records available from Chile; islands of the Central Pacific, mainly reports of nesting grounds. This is one of the sea turtles whose juvenile stages have most often been sighted, especially from intentional or incidental catches in commercial fishing gears used in coastal shallow waters, and from captures by scuba-divers. There are reports of multiple recapture of the same young individual at the same place. This would suggest that at least part of the population has residential or non-migratory behaviour.
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FAO species catalogue. Vol.11: Sea turtles of the world. An annotated and illustrated catalogue of sea turtlespecies known to date.Márquez M., R. FAO Fisheries Synopsis.  No. 125, Vol. 11. Rome, 1990 FAO. 81 p.
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Size

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Size: The mean straight carapace length (SCL) in adult females of this species ranges from 53 to 114 cm, but has been reported to be highly variable. [more...] Data for carapace length of males, range from 16 to 85 cm (Juveniles, adults). [more...] The body mass of turtles on nesting beaches, feeding grounds or in markets is difficult to obtain. [more...]
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FAO species catalogue. Vol.11: Sea turtles of the world. An annotated and illustrated catalogue of sea turtlespecies known to date.Márquez M., R. FAO Fisheries Synopsis.  No. 125, Vol. 11. Rome, 1990 FAO. 81 p.
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Brief Summary

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Hawksbill turtles live in clear, littoral waters of mainland and island shelves;they perform migratory movements that cause variations of population density in certain areas and seasons. Frequently, individuals of several year classes are found together on the same feeding grounds. Another feature of this species is that up to now, it has not been observed travelling in "flotillas". Studies on migrations have revealed short as well as long distance movements, at least for parts of the population; during the breeding period, the most common are short displacements between the nesting beach and the nearest offshore (feeding) bank, as in Tortuguero, Costa Rica, or slightly longer travels, i.e. from the same nesting beach to Miskito Cays in Nicaragua, from the nesting place on Isla Mujeres, Mexico, to Bani in the Dominican Republic (presumably the feeding ground), from Yucatan, Mexico to southern Cuba, from Nicaragua to Jamaica, and from northern Australia to Papua New Guinea. Migrations among the islands in Philippines, Indonesia, Java, or along Malaysia and Sarawak are probably performed by solitary turtles or by small groups, but no data are available. It is suspected that migrations also occur among the groups of islands of Oceania. The hawksbill turtle repeatedly has been considered a solitary nester; although it does not form real "arribazones", there are few nesting beaches where females arrive in larger groups- As in other sea turtles, the hawksbill shows nesting site fixity, which is more frequently observed among older individuals. However, subsequent nesting on beaches other than the original one also seems to be possible. Nesting occurs during the warm and rainy season, principally in summer, but it generally starts at the end of spring. This turtle has a nesting cycle of 2 or 3 years, with a mean around 2.6 years. Most hawksbills nest at night, but there are reports of day-time nesting, as well as basking behaviour, principally on uninhabited or low-inhabited beaches, such as those on Western Indian Ocean islands. In the Atlantic, there are several major nesting grounds, often located in the proximity of coral reefs, e.g. on the Yucatan Peninsula: Isla Aguada and Rio Lagartos, with at least 500 nests per year in each site. Other nesting areas are in southern Cuba, with several hundred nests; some islands of the Caribbean, such as: Jamaica, Dominican Republic, Turks and Caicos, and Grenada, each one with about 100 females nesting per year. The nesting grounds in northeastern Brazil are visited by about the same number of females each year. Some islands of the Indian Ocean, e.g., Seychelles, with over 600 nests or 300 turtles each year, British Indian Ocean Territory, with over 200 turtles, Comoro islands, with less than 100 turtles; Aldabra, with about 25 turtles, Amirantes, with about 150 turtles, Providence, with about 40 turtles, La Réunion, with about 50 turtles, Sri Lanka, with a few dozen turtles, southeast India (Tamil Nadu) with a few dozen turtles, and also the Maldives/Laccadives. in certain places, the presence of hawksbills is reported as "common", e.g., Iran, Somalia, Kenya, Tanzania, Madagascar and northern Mozambique. In the Eastern Indian Ocean, nesting occurs on the Andaman and Nicobar Islands and eastern Malaysia. Nesting apparently is more dispersed elsewhere, e.g. in the Indonesian Archipelago, with small concentrations quoted for southern Sumatra, Java,Bali, Sumbawa, and Celebes; in the Philippines (southern part of the Sulu Sea, on the "Philippine Turtle Islands", etc.); along Irian Jaya, Papua New Guinea, Solomon Islands, Fiji Islands, northern Australia and on the Leeward islands in the north of the Great Barrier Reef. Nesting has also been reported from the Pacific islands of Micronesia and Polynesia, but rarely from Hawaii. In the eastern Pacific, from Mexico to Panama, nesting is spread thinly, or rarely with small concentrations in the latter country and on the Mexican Pacific Islands. The nesting season occurs mostly toward the end of spring and throughout summer, usually before the peak of the green turtle season, sometimes another peak for the hawksbill appears after that of green turtle, e.g. in Tortuguero, Costa Rica. Some examples of timing of the nesting season are the following: Western Atlantic: coast of Mexico, from April to August, with a peak in May-June; Belize and Cuba same season as in Mexico, with a peak in June-August; Puerto Rico, from March to November; Jamaica, from May to September; Guatemala, from May to November, with a peak in June-August; Honduras, from June to September; Nicaragua, from May to October; in Costa Rica, from May to November, with a peak in May-June; US Virgin Islands, from June to December, with a peak in August-September; Turks and Caicos from April to August; Dominica Islands, from April to October; Guyana, Surinam and French Guiana, from May to August, with a peak in June-July; Colombia, from April to August (very few turtles today); Brazil, from December to March. Eastern Atlantic - Cabo Verde, from May to August. Western Indo-Pacific: Oman, from February to April; South Africa, from April to July; Comoro Islands, from October to June, with a peak in January-March; Seychelles, from September to January; Laccadives Islands, in October; India (Tamil Nadu), from September to February; Andaman islands, from October to December; Burma, from June to September; Philippines, from May to August; China, from March to April; Japan, from June to October; Palau, from July to August; New Hebrides, from September to January; New Caledonia, from November to March; Solomon Islands, from March to August; Irian Jaya, from May to September; Papua New Guinea, from March to September; Austral i a-Torres Strait, from December to February. Central Pacific Islands: Tokelau, from September-October; Micronesia, from May to September; Western Samoa, from September to February, with the peak in January to February; Fiji, from November to February. Eastern Pacific: Mexico, from May to October; EI Salvador, from July to December; Honduras, from August to November; Panama, from May to December; Ecuador Mainland, from December to May. Some reports quote renesting intervals of around two weeks, others of nearly three weeks. It is possible that both intervals are correct and that such periodicity depends of unknown internal and external factors. Also, in succeeding nesting periods, females may shift from one type of interval to another or show irregularities during the same nesting season. The interval most frequently quoted is the one extending for 2 weeks. For this species five or more subsequent nestings, with an average number of 2.3 clutches per season have been recorded. Judging from the total number of eggs per clutch, the hawksbill has the highest mean individual fecundity among sea turtles. When taking into account the number of times each female nests per season, together with the nesting cycle of 2-3 years, the fecundity of the hawksbill is comparable to that of the Kemp's ridley, which in average nests only 1.5 times per season but has a shorter nesting cycle of nearly every year. Pressure from predation probably has influenced the evolution of this feature; it is possible that mortality during incubation is higher in the hawksbill nests due to hazardous conditions of the nesting places, usually among bushes and farther from the surf zone, and hence, the increase in mortality must be compensated by higher fecundity. Also the leatherback lays fewer eggs, but the nesting place is very near to the surf zone. A comparative study is needed to clarify such parameters, but there is no doubt that higher fecundity is a biological compensation for high mortality. In hawksbills, the number of eggs per clutch is highly variable, and the data are also sometimes biassed by the presence of small and yolkless eggs, but never in substantial quantities as in the leatherback turtle. [more...] Egg diameters are often reported in the literature (range: 30 to 45 mm), but data on egg mass or weight of the clutch are relatively scarce (range: 20 to 31.6 g). [more...] The duration of the incubation in days varies among separated nesting beaches and also along the season. It may last from 47 to 75 days, depending on the place and time. [more...] Data on size and body mass of hatchlings range from 38 to 46 mm, and from 8 to 17.9 g; respectively. [more...] Hatchlings emerge mainly during the first hours of the night, when sand temperature is below 28°C, above this temperature their activity is inhibited. As in the other species, the small turtles run rapidly to the surf zone; after reaching the sea they disappear for an unknown period and are again observed when approaching coastal shallow waters at sizes usually over 20 em of carapace length (SCL). Age at sexual maturity is uncertain; old reports quote ages from 3 to 4.5 years, but these figures were obtained from turtles reared in captivity, and it is assumed that for wild stocks they must be much higher. Furthermore, the figures for age at first maturity should be different if they are correlated to the mean carapace lengths observed on nesting beaches and if all size data are obtained from measurements of straight carapace lengths. Under such circumstances, the first maturity of females should be reached at sizes between 68 and 80 cm (SCL) and at body weights from 40 to 56 kg depending on the locality. It is suggested that males reach maturity at similar sizes but no data are available to confirm this assumption. There are few reports on courtship and mating; both have been observed in shallow waters. During mating, the male holds the female by using its claws and tail, and this operation may last several hours. It has been observed that females are more receptive after nesting and that they commonly receive attention from several males without having preference for any special partner. Hence, polygamy is the normal pattern. The optimal incubation temperatures recorded on Campbell Island, Australia range from 27.3°-31.8°C (at 50 cm depth, at the bottom of the nest) and from 28.9° - 32.4°C (at 30 cm depth, at the side of the egg mass). Figures from Eastern Samoa showed an increase of 3.6° (range 2.7-5°C) above the sand temperature at equal depth. On Isla Aguada, Mexico, ambient temperature and sand egg mass temperature were closely correlated, the changes in temperature of the egg mass normally dephasing by several hours; however, abrupt temperature decreases were observed during rainfall. The incubation temperature in translocated nests ranged from 27.20 to 33.5°C (n a 54 clutches) throughout the 1985 season, and from 28.5° to 30.5°C (n a 32 clutches) for the second third of the incubation period in 1986. Studies on sex determination related to incubation temperature are currently in progress on the Isla Aquada nesting beach (Mexico); no data are available for other nesting beaches. The critical, pivotal or threshold temperature and time at which the sex of the hatchling is determined apparently is one or two degrees lower than for other sea turtles (29° or 30° C), because the hawksbill is prone to nest in shadowy places; to balance the sex-ratio, mechanisms other than temperature must be brought into play.

As the other sea turtles, this species is subjected to predation throughout its life-cycle. The eggs and embryos are consumed by several species of ghost crabs (Ocypode sp.), nearly throughout the nesting range, on the mainland as well as on insular beaches; predation also affects the hatchlings in and outside the nest. Mammals like genets and mongooses are reported as predators of eggs in the Indian Pacific Islands, South Africa and also in the US Virgin Islands, Barbados and Guadaloupe, where the introduced mongoose (Herpestes sp.) is one of the main causes of predation; skunks and raccoons are common on beaches of Mexico and are quoted as predators of nests and hatchlings. Iguanas are reported on beaches of Cuba, and although direct predation has not been observed, it is possible that these reptiles eat the rest of the nest following the predation by other animals such as raccoons. In some areas, rats are reported as potential predators (the Polynesian rat - Rattus exulans). Jackals, pigs and feral dogs also dig out nests, the latter two in connection with the presence of human dwellings in the neighbourhood of the nesting beaches. Monitor lizards (Varanus sp.) are important nest predators on mainland Africa, India, Cambodia, northern Australia, the Philippines, and Andaman/Nicobar Islands. Birds such as frigates, herons, vultures, kites, crows, etc., eat hatchlings when they emerge in day-time. The barn owl (Tyto alba) is quoted as a crepuscular predator of hatchlings in the Comoro Archipelago. In the water, hatchlings are captured by sea birds (frigates, gulls, etc.), and carnivore fishes, e.g., tunas, dolphin-fish and jacks, or sharks as was documented for Sarawak and Samoa. Because of its occurrence around coral reefs, where big carnivore fishes remain in ambush, this turtle is continuously exposed to heavy predation, and not only hatchlings, but also juveniles and adults are attacked by those big carnivores, principally sharks (e.g. the tiger shark Galeocerdo cuvier). Apart from predation, no other kinds of natural mortality have been documented, and there are no reports on dermic papillomae. Commonly these turtles are covered by epibiotic organisms, e.g., green algae sometimes form a rug over the carapace in old individuals; also leeches, barnacles, small pelagic crabs, other crustacea and nudibranchs are often observed.This is a carnivorous turtle, commonly poking in crevices between rocks and corals, so the diet often is highly variable. Up to around 10 cm of SCL the hawksbill apparently is a nectonic animal, and when it approaches coastal areas, it changes over to benthic feeding, and becomes a regular inhabitant of hard substrata where its diet consists principally of corals, tunicates, algae, and sponges. Some data on stomach contents from several studies are the following: a) Juveniles: for Salvage Island (Canary Archipelago), coelenterates (Anemonia, hydroids, siphonophora, especially Velella, hydromedusae), algae (Stypodium, Sargassum, Dyctiota, cyanophytes), gastropods (Littorina, Amyclina, Janthina), cephalopods (Taonius, Histioteuthis, Oegopsida), sponges (2 species), spider crabs (inachus), sea urchins, stones, and plastic materials; for Taiwan Island, algae, shells, and bark. b) Subadults: for Magdalena Bay, Mexico, crustaceans and red lobsterets (Pleuroncodes); for Australia (subadults and adults), ascidians, encrusting animals and algae; for French Guiana, sponges, tunicates, coelenterates, molluscs, algae, and angiospermes; for Ascension Islands, Costa Rica (Tortuguero), Hawaii (3 samples), Seychelles, Aldabra, Oman, Cousin Islands, mainly sponges (Demospongia group); for Honduras: mangrove leaves and fruits, bark and wood; for New Zealand, barnacles, cephalopods, siphonophores (Velella), and tunicates (Salpa); for the Philippines, seagrass and sponges, (Echeuma, Codium); for Sri Lanka, algae, corals, gastropods, and ascidians; for the Seychelles, sargassum weeds, sponges and algae; for South Yemen, green algae. Comprehensive studies of the diet were made by Carr and Stancyk (1975), and their conclusion for the Tortuguero hawksbill's population was that it consists mainly of sponges of the group Demospongia, and that competition with other species within this niche is rare; in fact, Eretmochelys is the only known spongivore marine reptile (Meylan, 1988); and strictly spongivore vertebrates include only a small number of teleostean fishes.

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FAO species catalogue. Vol.11: Sea turtles of the world. An annotated and illustrated catalogue of sea turtlespecies known to date.Márquez M., R. FAO Fisheries Synopsis.  No. 125, Vol. 11. Rome, 1990 FAO. 81 p.
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Benefits

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Interest to Fisheries: The hawksbill is a unique species, because in addition to all the products commonly obtained from other sea turtles, it also yields the brightly-coloured, thick scutes covering the carapace, which are of high value in the international market. These flexible scutes, the so-called "carey" or "tortoise-shell" are mainly used in jewellery. The term "tortoise-shell" applies to the raw material of scutes, while "carey" refers to the worked tortoise-shell. in the old world, this species has been exploited since the pharaonic period, and in China its exploitation dates back to still more ancient times. From China it was introduced to Japan in the Nara Period (A.D. 745-784) in the form of ornamental articles reserved exclusively for the aristocracy to symbolize a high status of nobility. Handicrafts made of tortoise-shell appear to have florished in many ancient cultures, in places like Ceylon, India, Rome, Oceania, etc. In many other cultures, the hawksbill and other sea turtles, were exploited only for their meat and eggs. Up to the sixties and seventies of this century, the commerce of the tortoise-shell, raw and worked, showed an extraordinary increase, and many countries were engaged in the export-market to Hong Kong, Japan, Singapore, China and Korea, in Asia, and to Italy, West Germany, France, the UK and Spain, in Europe. Also the market for stuffed turtles had increased to incredible numbers up to recent years. In the presence of such a global market it is actually surprising that there are still hawksbill turtles left in the tropical seas of the world. No precise figures are available for the huge quantities of raw and worked tortoise-shell and of stuffed hawksbill turtles commercialized in the past two decades (60's and 70's), but it is known that about 90% of the products were imported by Japan; part of this is documented by the Japanese Custom Statistics. The internal market in each country is difficult to evaluate because of the dispersed nature of the handicraft industry. Tortoise-shell and carey are processed in small-scale indigenous industries of Southeast Asia, the Caribbean, the Seychelles, Micronesia (Oceania), and elsewhere; they produce low-quality souvenir trinkets, carved directly on the backshell scutes. But the bekko Japanese craftsmen elaborately shape the scutes, hooves and plastron pieces and blend the natural colours, using a technique combining water, steam, heat and pressure. Only the French and Italian artisans are known to employ similar techniques to produce high-quality products- Historically, the bekko jewellery was dedicated to the hair ornament of Japanese brides. Today, a huge variety of designs of jewellery, eyeglass frames, inlay boxes, combs, pins, etc., are produced and used nearly exclusively for domestic consumption in Japan. Because of the peculiarity of the hawksbill market, any size of turtles are captured, the smaller ones for stuffing and the big ones for the scutes, and in many places also for the meat and the eggs. Today, the commerce with eggs is prohibited in many of the countries. With the CITES restrictions, the exports of carey scutes, particularly since 1979, have decreased substantially, and only few countries retain a reservation effective for the hawksbill, and hence continue importing its products- In the majority of the former exporter countries, the commerce today is reduced to the internal demand mainly for meat and tortoise-shell. Complete and up-to-date statistics for each country are not available, but the importation of hawksbill scutes by Japan in 1987 and 1988 was published in the newsletter of Traffic (USA) in January 1989, and according to that the most important exporter was Cuba with 13 905 kg for both years, followed by Haiti, with 7 641 kg, the Maldives, with 7 436 kg, the Solomon Islands, with 7 369 kg, Jamaica, with 6 827 kg, the Comoro Islands, with 4 566 kg, Fiji, with 2 837 kg, Singapore, with 1 009 kg. All the other countries trading in hawksbill scutes were exporting less than one metric ton per year, e.g. St. Vincent, Ethiopia, Dominican Republic, Grenada, Antigua - Barbuda and Brunei. In 1987, other very important former exporters became parties of CITES: Indonesia, Philippines, Singapore the Dominican Republic. The total imports by Japan, of carey scutes, for these two years were: 29 808 kg in 1987 and 25 043 kg in 1988 (up to November only). A very important market for stuffed hawksbills was developed during the seventies. The importation of stuffed turtles by Japan was increasing from 9 329 kg in 1970 to a maximum of 85 843 kg in 1983; after that year, the imports steadily decreased, down to 8 855 in 1986, and a total ban is expected during 1989. The principal exporters between 1970 and 1986 were: Indonesia, Singapore (until 1984), China (Taiwan Island), Philippines (until 1980) and Hong Kong. The size of stuffed turtles is highly variable, usually juveniles are used for this purpose, but often also big adults appear on the market. Since the ratio for converting dry weights (stuffed turtles) to live weights is not yet available, the total number of turtles used for this market is still unknown. For statistical purposes, the stuffed hawksbill is called in Japan " worked bekko" to distinguish it from the "worked tortoise-shell", which includes all the stuffed species except the hawksbill. In the FAO Yearbook of Fishery Statistics, catches of Eretmochelys imbricata are reported only for the Western Central Atlantic (Fishing Area 31 ), totalling 318 metric tons in 1987 mostly by Cuba (277 metric tons) and the Dominican Republic, 41 metric tons. These data refer to entire animals. If we compare the statistics of hawksbill imports reported by Japan, with the data reported by FAO, the latter appear to be very incomplete. It is possible that hawksbill catches are included under the item "Marine turtles n.e.i." (unidentified species) but it is not possible, at present, to calculate the proportion of hawksbilIs in the catches. As with other species of sea turtles, the hawksbill is usually captured by turning over the females when they crawl onto the beach to nest. This method is widely used by riparian people nearly everywhere the hawksbill nests. The harpoon is another common method to capture turtles, but nowadays, entangling nets of different mesh-sizes, made of natural fibres or monofilament-nylon, are becoming a more effective and less time-consuming fishing gear. Not withstanding their great diversity, these nets have some common features, especially the large mesh-size and the light bottom-lines that allow the captured turtles to reach the water surface and breathe. Length and depth are variable and usually several nets are joined to enlarge the area covered; also floating decoys are used in the head line to attract males. Seines with finer mesh are set to surround the turtles in forageing areas. Scuba-diving is of special importance in the capture of this species, but the use of spear-guns is more popular and productive around reefs; harpoons, hooks and ropes are used also by divers. Remoras were used by Caribbean people even before the discovery of America, and this fish, known as "pega-pega" on the Spanish-speaking islands of the Caribbean, was or still is, used in other places such as Sri Lanka, Kenya, Yemen, Somalia, Madagascar and northern Australia. Eggs are collected directly on the nesting beaches, while the meat comes from overturned females or turtles captured at sea. The skin is of lower quality than that of the olive ridley. Among coral-reef organisms consumed by man, a small number is considered to be toxic, and one of these is the hawksbill turtle. In some places, these turtles are avoided as food because of the high risk of intoxication. Apparently, a high percentage of fatalities resulting from the consumption of hawksbill meat has occurred in the Indo-Pacific region, Oceania; two fatal cases were quoted for the Caribbean in 1967, but the species of turtle that caused them was not identified. in some of the reported cases, the other species implicated is Chelonia mydas. Poisoning by hawksbills has been quoted by several authors and in some cases, a great number of deaths were reported, mainly in India, Sri Lanka, China (Taiwan Island), Philippines, Indonesia, Papua/New Guinea, northern Australia (Torres Strait), Central Pacific (Arorue, Gilbert Islands), and Caribbean (Windward Islands). Intoxications were also produced by the green turtle Chelonia mydas, and some other cases were caused by unidentified species. In a short paper produced in Australia by Limpus (1987), general information is offered on the toxine, the medical aspects of the intoxication, treatment and prevention, and it is recommended not to eat hawksbill turtle meat in areas where toxicity has been reported. The total catch reported for this species to FAO for 1999 was 15 t. The countries with the largest catches were Cuba (8 t), Grenada (5 t) and Fiji Islands (2 t)
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FAO species catalogue. Vol.11: Sea turtles of the world. An annotated and illustrated catalogue of sea turtlespecies known to date.Márquez M., R. FAO Fisheries Synopsis.  No. 125, Vol. 11. Rome, 1990 FAO. 81 p.
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Hawksbill sea turtle

provided by wikipedia EN

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 subspeciesE. i. imbricata and E. i. bissa, respectively.[2]

The hawksbill's appearance is similar to that of other marine 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, primarily as a result of Human fishing practices, classifies E. imbricata as critically endangered.[1] Hawksbill shells were the primary source of tortoiseshell 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.[3]

Anatomy and morphology

Photo from above of swimming turtle, with four outstretched flippers and faceted shell
Carapace's serrated margin and overlapping scutes are evident in this individual

Adult hawksbill sea turtles typically grow to 1 m (3 ft) in length, weighing around 80 kg (180 lb) on average. The heaviest hawksbill ever captured weighed 127 kg (280 lb).[4] 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.[5]

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 forelimbs have two visible claws on each flipper.

Profile photo of animal head with prominent beak protruding above lower jaw, a faceted head covering surrounds the eye
Close-up of the hawksbill's distinctive beak

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 m (3 ft) in length.[6] The hawksbill appears to frequently employ its sturdy shell to insert its body into tight spaces in reefs.[7]

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.[8][9]

Due to its consumption of venomous cnidarians, hawksbill sea turtle flesh can become toxic.[10]

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.[11][12]

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 major subpopulations are known, in the Atlantic and Indo-Pacific.[13]

This world map shows concentrated nesting sites in the Caribbean and northeast coast of South America. Many other sites are spread across South Pacific islands, with other concentrations in the Red Sea and Persian Gulf, China's East coast, Africa's southeast coast and Indonesia.
Another model of the possible distribution of E. imbricata: Red circles represent known major nesting sites. Yellow circles are minor nesting sites.

Atlantic subpopulation

Photo of turtle swimming with extended flippers
Hawksbill sea turtle in Saba, Netherlands Antilles

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.[13][14][15] They live off the Brazilian coast (specifically Bahia, Fernando de Noronha) through southern Florida and the waters off Virginia.[4]

In the Caribbean, the main nesting beaches are in the Lesser Antilles, Barbados,[16] Guadeloupe,[17] Tortuguero in Costa Rica,[18] and in the Yucatan. They feed in the waters off Cuba[19] and around Mona Island near Puerto Rico[20] among other places.

Indo-Pacific subpopulation

In the Indian Ocean, hawksbills are a common sight along the east coast of Africa, including the seas surrounding Madagascar and nearby island groups, and all along the southern Asian coast, including the Persian Gulf, the Red Sea, and the coasts of the Indian Subcontinent and Southeast Asia. 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 most important hatcheries of its kind along with olive ridley sea turtles in the archipelagic country of the Philippines.[21] A small group of islands in the southwest of the archipelago has been named the "Turtle Islands" because two species of sea turtles nest there: the hawksbill and the green sea turtle.[22] In January 2016, a juvenile was seen in Gulf of Thailand.[23] A 2018 article by The Straits Times reported that around 120 hawksbill juvenile turtles recently hatched at Pulau Satumu, Singapore.[24] Commonly found in Singapore waters, hawksbill turtles have returned to areas such East Coast Park and Palau Satumu to nest.[25] In Hawaii, hawksbills mostly nest on the "main" islands of Oahu, Maui, Molokai, and Hawaii.[26] In Australia, hawksbills are known to nest on Milman Island in the Great Barrier Reef.[27] Hawksbill sea turtles nest as far west as Cousine Island in the Seychelles, where the species has been legally protected since 1994, and the population is showing some recovery.[28] The Seychelles' inner islands and islets, such as Aldabra, are popular feeding grounds for immature hawksbills.[9][29]

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.[13] Nonetheless, as recently as 2007, the species had been considered largely extirpated in the region.[30] Important remnant nesting and foraging sites have since been discovered in Mexico, El Salvador, Nicaragua, and Ecuador, providing new opportunities for research and conservation. 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 (El Salvador), Gulf of Fonseca (Nicaragua, El Salvador, and Honduras), Estero Padre Ramos (Nicaragua), and the Gulf of Guayaquil (Ecuador).[31] Multi-national initiatives, such as the Eastern Pacific Hawksbill Initiative, 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.[6][32] 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.[33]

Feeding

Photo of swimming turtle with extended head
E. imbricata in a coral reef in Venezuela

While they are omnivorous, sea sponges are their principal food; they constitute 70–95% of the turtles' diets.[34] 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.[35] Aside from sponges, hawksbills feed on algae, cnidarians, comb jellies and other jellyfish, and sea anemones.[6] 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' armored heads.[4]

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 (often lethally) toxic to other organisms. In addition, hawksbills choose sponge species with significant numbers of siliceous spicules, such as Ancorina, Geodia (G. gibberosa[4]), Ecionemia, and Placospongia.[35]

Life history

Photo of swimming turtle
Young E. imbricata from Réunion Island
 src=
A female hawksbill turtle laying eggs on beach at Mona island, Puerto Rico

Not much is known about the life history of hawksbills.[36] 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.[37][38] The pelagic phase possibly lasts until the turtles reach around 20 cm in length in 1–3 years,[39] reaching sexual maturity at around 40 cm (2–4 years).[40] Hawksbills show a degree of fidelity after recruiting to the benthic phase,[41] however movement to other similar habitats is possible.[42]

Breeding

 src=
Hawksbill baby turtle in Paulista, Pernambuco, Brazil

Hawksbills mate biannually in secluded lagoons off their nesting beaches in remote islands throughout their range. The most significant nesting beaches are in Mexico, the Seychelles, Indonesia, and Australia. Mating season for Atlantic hawksbills usually spans April to November. Indian Ocean populations, such as the Seychelles hawksbill population, mate from September to February.[9] 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.[6][14] Their nests can be found throughout beaches in about 60 countries.

The baby turtles, usually weighing less than 24 g (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 cm (0.98 in) long. They instinctively crawl 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.[6]

Photo of small turtle walking across sand
Hawksbill hatchling in Puerto Rico

Maturity

Hawksbills evidently reach maturity after 20 years.[14] Their lifespan is unknown.[43] Like other sea turtles, hawksbills are solitary for most of their lives; they meet only to mate. They are highly migratory.[36] Because of their tough carapaces, adults' only predators are sharks, estuarine crocodiles, octopuses, and some species of pelagic fish.[36]

A series of biotic and abiotic cues, such as individual genetics, foraging quantity and quality,[44] or population density, may trigger the maturation of the reproductive organs and the production of gametes and thus determine sexual maturity. Like many reptiles, all marine turtles of a same aggregation are highly unlikely to reach sexual maturity at the same size and thus age.[45] Age at maturity has been estimated to occur between 10[46] and 25 years of age[47] for Caribbean hawksbills. Turtles nesting in the Indo-Pacific region may reach maturity at a minimum of 30 to 35 years.[48][49]

Evolutionary history

Within the sea turtles, E. imbricata has several unique anatomical and ecological traits. It is the only primarily spongivorous reptile. Because of this, its evolutionary position is somewhat unclear. Molecular analyses support placement of Eretmochelys within the taxonomic tribe Carettini, which includes the carnivorous loggerhead and ridley sea turtles, rather than in the tribe Chelonini, which includes the herbivorous green turtle. The hawksbill probably evolved from carnivorous ancestors.[50]

Etymology and taxonomic history

Fanciful drawing showing seven turtles, with a variety of carapaces and body shapes
Hawksbill sea turtle (top right) in a 1904 plate by Ernst Haeckel

Linnaeus originally described the hawksbill sea turtle as Testudo imbricata in 1766, in the 12th edition of his Systema Naturae.[51] In 1843, Austrian zoologist Leopold Fitzinger moved it into genus Eretmochelys.[52] In 1857, the species was temporarily misdescribed as Eretmochelys imbricata squamata.[53]

Two subspecies are accepted in E. imbricata's taxon. E. i. bissa (Rüppell, 1835) refers to populations that reside in the Pacific Ocean.[54] The Atlantic population is a separate subspecies, E. i. imbricata (Linnaeus, 1766). The nominate subspecies is the Atlantic taxon, because Linnaeus' type specimen was from the Atlantic.[55]

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.[56] Caretta is the genus of the hawksbill's much larger relative, the loggerhead sea turtle.

Exploitation by humans

Photo of dish
Palauan women's money (toluk)

Throughout the world, hawksbill sea turtles are taken by humans, though it is illegal to hunt them in many countries.[57] In some parts of the world, hawksbill sea turtles are eaten as a delicacy. As far back as the fifth century BC, sea turtles, including the hawksbill, were eaten as delicacies in China.[58]

 src=
Capture Hawksbill sea turtle from Mauritius , Customs Orly Airport 1995

Many cultures also use turtle shells for decoration. These turtles have been harvested for their beautiful shell since Egyptian times, and the material known as tortoiseshell is normally from the hawksbill.[59] In China, where it was known as tai mei, the hawksbill is called the "tortoise-shell turtle", named primarily for its shell, which was used for making and decorating a variety of small items, as it was in the West.[58] Along the south coast of Java, stuffed hawksbill turtles are sold in souvenir shops, though numbers have decreased in the last two decades.[60] In Japan, the turtles are also harvested for their shell scutes, which are called bekko in Japanese. It is used in various personal implements, such as eyeglass frames and the shamisen (Japanese traditional three-stringed instrument) picks.[59] In 1994, Japan stopped importing hawksbill shells from other nations. Prior to this, the Japanese hawksbill shell trade was around 30,000 kg (66,000 lb) of raw shells per year.[19][61] In the West, hawksbill sea turtle shells were harvested by the ancient Greeks and ancient Romans for jewellery, such as combs, brushes, and rings.[62] The bulk of the world's hawksbill shell trade originates in the Caribbean. In 2006, processed shells were regularly available, often in large amounts, in countries including the Dominican Republic and Colombia.[63]

The hawksbill sea turtle appears on the reverse side of the Venezuelan 20-bolivar and the Brazilian 2-reais banknotes. A much-beloved fountain sculpture of a boy riding a hawksbill, affectionately known as Turtle Boy, stands in Worcester, Massachusetts.

Conservation

Photo of turtle swimming in shallow, green water
A hawksbill sea turtle in Tobago

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. Biologists estimate that the hawksbill population has declined 80 percent in the past 100–135 years.[1] Human and animal encroachment threatens nesting sites, and small mammals dig up the eggs to eat.[6] In the US Virgin Islands, mongooses raid hawksbill nests (along with those of other sea turtles, such as Dermochelys coriacea) right after they are laid.[64]

In 1982, the IUCN Red List of Threatened Species first listed E. imbricata as Endangered.[65] This endangered status continued through several reassessments in 1986,[66] 1988,[67] 1990,[68] and 1994[69] until it was upgraded in status to Critically Endangered in 1996.[1] Two petitions challenged its status as an endangered species prior to this, claiming 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 the worldwide hawksbill sea turtle population had declined by 80% in the three most recent generations, and no significant population increase occurred 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.[70]

The species (along with the entire family Cheloniidae) has been listed on Appendix I of the Convention on International Trade in Endangered Species.[3] It is prohibited to import or export turtle products, or to kill, capture, or harass hawksbill sea turtles.[57]

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[71] since 1970. The US government established several recovery plans[72] for protecting E. imbricata.[73]

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Hawksbill sea turtle: Brief Summary

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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. 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, primarily as a result of Human fishing practices, classifies E. imbricata as critically endangered. Hawksbill shells were the primary source of tortoiseshell 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.

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Distribution

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cosmopolitan warm water
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van der Land, J. (ed). (2008). UNESCO-IOC Register of Marine Organisms (URMO).
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Jacob van der Land [email]