The 'hawksbill turtle' ('''Eretmochelys imbricata''') is a
critically endangered sea turtle belonging to the family
Cheloniidae. It is the only species in its
genus. The species itself has a worldwide distribution, but the
Atlantic and
Pacific populations are divided into two
subspecies. ''Eretmochelys imbricata imbricata'' is the subspecies that includes the Atlantic hawksbill turtle populations and the subspecies ''Eretmochelys imbricata bissa'' refers to the collective population of hawksbill turtles found in the Pacific Ocean.
[1]
The hawksbill's appearance is similar to that of other marine turtles. It has a generally flattened body shape, a protective
carapace, and its
flipper-like arms are 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. While the turtle lives a part of its life in the open ocean, it is most often encountered in shallow lagoons and
coral reefs where it feeds on its chosen prey,
sea sponges. Some of the sponges eaten by ''E. imbricata'' are known to be highly toxic and lethal when eaten by other organisms. In addition, the sponges that hawksbills eat are usually those with high
silica content, making the turtles one of few animals capable of eating siliceous organisms. They also feed on other
invertebrates, such as
comb jellies and
jellyfish.
Because of human fishing practices, ''Eretmochelys imbricata'' populations around the world are threatened with
extinction and the turtle has been classified as
critically endangered by the
World Conservation Union.
Several countries, such as
China and
Japan, have valued hunting hawksbill turtles for their flesh, which is considered good eating. Hawksbill turtle shells, the primary source of ''tortoise shell'', is used for decorative purposes. By the
Convention on International Trade in Endangered Species, it is illegal to capture and to trade in hawksbill turtles and products derived from them in many nations.
Anatomy and morphology
''Eretmochelys imbricata''. The carapace's serrated margin and overlapping scutes are evident in this individual.
''Eretmochelys imbricata'' has the typical appearance of a marine turtle. Like the other members of its family, it has a depressed body form and
flipper-like limbs adapted for swimming. Adult hawksbill turtles have been known to grow up to a meter in length, weighing around 80 kilograms on average. The heaviest hawksbill ever captured was measured to be 127 kilograms.
[2] 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.
[3]
The hawksbill turtle has several characteristics that distinguish it from other, closely-related species. Its elongated, tapered head ends in a
beak-like mouth (from which its common name is derived), its beak more sharply pronounced and hooked than other sea turtles. The hawksbill's arms have two visible claws on each flipper.
A close-up of the hawksbill's distinct beak.
One of the hawksbill's more-easily distinguished characteristics is the pattern of the thick
scutes that make up its carapace. While its carapace has five central scutes and four pairs of
lateral scutes like several members of the same family, ''E. imbricata's 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 itself has been known to reach almost a meter in length.
[4]
The sand tracks of hawksbill turtles are asymmetrical, as they crawl on land with an alternating gait. This is opposed to the
green sea turtle and the
leatherback turtle, which crawl rather symmetrically.
[5][6]
Due to its consumption of venomous
cnidarians hawksbill turtle flesh can reach certain levels of
toxicity.
[7]
Distribution
Hawksbill 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 tropical waters. Two major
subpopulations are acknowledged to exist, the Atlantic and Indo-Pacific subpopulations.
[8]
Another model of the possible distribution of ''E. imbricata''. Red circles represent known major nesting sites. Yellow circles are minor nesting sites.
Atlantic subpopulation
In the Atlantic, ''E. imbricata'' populations can be seen as far west as the
Gulf of Mexico and the species' eastern range reaches up to the southern tip of the
African continent.
[9] The northern limits of the species' range can go as far north as
Long Island Sound[10] along the northern border of the
United States. On the other side of the Atlantic, hawksbills have been sighted in the frigid waters of the
English Channel, the species' northernmost occurrence to date. Their southern reach is known all the way to the
Cape of Good Hope in Africa.
[11]
In the
Caribbean, they are known from the
Brazilian coast (specifically
Bahia), southern
Florida and
Hawaii. They have also been seen on the beaches of
Antigua and Barbuda.
has its share of ''E. imbricata'' nesting sites, specifically in the vicinity of
Tortuguero.
[12] The island of
Cuba is a known feeding ground for the Caribbean hawksbill turtle population.
In
Puerto Rico, the waters around
Mona Island serve as feeding grounds for Caribbean ''E. imbricata''.
[13] While a tropical species, ''E. imbricata'' has been found in areas in the
United States within higher latitudes, such as
Massachusetts and
Long Island Sound.
They have also been seen in the waters off
Virginia.
Indo-Pacific subpopulation
The species' Indo-Pacific population is widespread throughout the entire region. In the
Indian Ocean, hawksbills are a common sight all along the east coast of the African continent, including the seas surrounding
Madagascar and nearby island groups. The species' Indian Ocean range stretches all the way along the coast of
Asia, including the
Persian Gulf and the
Red Sea, along the entire coast of the
Indian subcontinent, across the entire
Indonesian archipelago and the northwestern coast of
Australia. The
Pacific range of ''E. imbricata'' is somewhat limited to the ocean's tropical and subtropical regions. Its northernmost reach in the region are the waters off the southwestern tip of the
Korean peninsula and the
Japanese archipelago. The range continues, enveloping the entire region of
Southeast Asia, the entire northern coast of Australia all the way south to the northern part of
New Zealand. Across the Pacific, hawksbills are known as far north as the
Baja peninsula in
Mexico, along the waters off the Central American and South American coast to the northern tip of
Chile.
In the
Philippines, there are several known nesting sites for the species. Hawksbill turtle hatchlings have been found on the island of
Boracay.
[14] A small group of islands in the southwest of the
archipelago have been named the "
Turtle Islands" precisely because they are known nesting grounds for two species of sea turtle, including ''Eretmochelys imbricata''. (The other being the
green sea turtle, ''
Chelonia mydas''.)
[15] In
Australia, ''E. imbricata'' are known to nest on
Milman Island in the
Great Barrier Reef.
[16] In the
Indian Ocean, hawksbill turtles have been found to nest as far west as
Cousine Island in the
Seychelles, where the species has been legally protected since 1994. The Seychelles' inner islands and islets, such as
Aldabra Island, are ripe feeding grounds for immature hawksbills.
Ecology and life history
Habitat
Adult hawksbill 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 have also been encountered in a wide range of habitats, from the open ocean to lagoons and even mangrove swamps in estuaries.
While much is not known about the habitat preferences of early-life stage ''E. imbricata'', like other sea turtles' young, they are assumed to be completely pelagic and thus make the open sea their home until they mature.
[19]
Feeding ecology
''E. imbricata'' in a coral reef in
Tortuga.
While they are known to be omnivorous, the principal food of hawkbill turtles are
sponges. Sponges constitute 70–95% of the diets of ''E. imbricata'' populations in the
Caribbean. However like many
spongivores, ''E. imbricata'' feed only on a few select species, and will ignore many others. The Caribbean hawksbill populations were found to feed primarily on sponges from the class
Demospongiae, specifically ones belonging to the orders
Astrophorida,
Spirophorida and
Hadromerida.
[20] Select sponge species known to be fed on by these turtles include ''
Geodia gibberosa''.
Aside from sponges, hawksbills also feed on algae and
cnidarians like
jellyfish and
sea anemones.
The hawksbill is also known to 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, for Man o' War's
stinging cells cannot penetrate the turtles' armoured heads.
''Eretmochelys imbricata'' have shown themselves to be highly resilient and resistant to their prey. Some of the sponges known to be eaten by hawksbills, such as ''
Aaptos aaptos'', ''
Chondrilla nucula'', ''
Tethya actinia'', ''
Spheciospongia vesparum'' and ''
Suberites domuncula'', are highly (often lethally)
toxic to other organisms. In addition, hawksbills are known to choose sponge species that have a significant amount of
siliceous spicules, such as ''
Ancorina'', ''
Geodia'', ''
Ecionemia'' and ''
Placospongia''.
Life history
Much is not known about the life history of ''Eretmochelys imbricata''.
[21] Hawksbills are known to mate biyearly in secluded lagoons in remote islands throughout their range. Mating season for Atlantic hawksbills usually takes place from April to November. For Indian Ocean populations such as the
Seychelles hawksbill population, the mating season is from September to February.
As with other sea turtles, hawksbills mate in shallow lagoons off the shores of their prospective nesting beaches. After mating, the females drag their heavy bodies high onto the beach during the night. They will then clear out an area and dig a nesting hole using their rear flippers. The female then lays a
clutch of eggs in the nest and then covers them with sand.
Caribbean and
Florida nests of ''E. imbricata'' normally contain around 140 eggs. After the several-hour-long process, the female then returns to the sea. This is the only time when hawksbill turtles are known to leave the ocean.
The baby turtles, usually weighing less than two dozen grams, hatch during the night after around two months. These newly-emergent
hatchlings are darkly-colored, with heart-shaped carapaces measuring around 2.5 centimeters (1 in) long. They instinctually head for the sea, attracted by the reflection of the moon on the water (a mechanism which can be disrupted by
anthropogenic 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 predators such as
shorebirds and
shore crabs.
''E. imbricata'' hatchling in
Grenada.
The early
life history of juvenile hawksbill turtles is unknown. Upon reaching the sea, the hatchlings are assumed to enter a
pelagic life stage (like other
marine turtles) for an undetermined amount of time. While hawksbill turtle growth rates are not known, when ''E. imbricata'' juveniles reach around 35 cm, they switch from a pelagic life style to a coral reef-associated one. Hawksbill turtles are hypothesized to reach maturity after thirty years.
While there is no clear consensus because of a lack of data, hawksbill turtles are believed to live from thirty to fifty years in the wild.
[22] Like other sea turtles, hawksbill turtles are solitary for most of their lives, they only group together to mate. They were once thought to be habitual, but they are now known to be highly
migratory.
Because of their tough
carapaces, hawksbill turtles have no major predators as there are few creatures that are capable of biting through their protective shell.
Sharks and
estuarine crocodiles are a few of their natural predators.
Octopuses and some species of pelagic fish have also been known to prey on the adult turtles.
Evolutionary history
Within the sea turtles, ''Eretmochelys imbricata'' has several unique
anatomical and
ecological traits, including being the only primarily
spongivorous reptle known. Because of this, its evolutionary position has been somewhat unclear. Molecular analyses supports the probability that the Eretmochelydae evolved from carnivorous ancestors rather than herbivorous ones. As the
taxonomic tribe Carettini is composed of
carnivorous species (such as the
loggerhead turtle), the hawksbill most probably evolved from them instead of the
herbivorous Chelonini, which includes the
green turtle.
[23]
Etymology and taxonomic history
The hawksbill turtle was originally described by
Carolus Linnaeus as ''Testudo imbricata'' in 1766.
[1] It was moved into the genus ''Eretmochelys'' by the Austrian zoologist
Leopold Fitzinger in 1843.
[25] In 1857, the species was redescribed as ''Eretmochelys imbricata squamata'', a designation that is now invalid.
[26]
There are two accepted
subspecies in the ''E. imbricata''
taxon. ''Eretmochelys imbricata bissa''
(Rüppell, 1835) refers to all known populations of the ''Eretmochelys imbricata'' that reside in the
Pacific Ocean.
[27] The
Atlantic population has been found to be a separate subspecies, ''Eretmochelys imbricata imbricata''
(Linnaeus, 1766). The subspecies name of ''imbricata'' was retained because the
type specimen that Linnaeus used to initially describe the species was from the Atlantic.
[28]
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'' and the term referred to the then-species' being the second species in the genus.
[29] ''
Caretta'' is the genus of the hawksbill's much larger relative, the
loggerhead turtle.
Importance to humans
A Japanese tortoiseshell ornament.
Throughout the world, hawksbill turtles are taken by humans even though it is illegal to hunt them in many countries.
In some parts of the world, hawksbill turtles are taken and eaten as a delicacy. As far back as the fifth century B.C., sea turtles including the hawksbill were eaten as delicacies in
China.
[30]
Many cultures also use the turtles' shells for decoration. In China where it was known as ''tai mei'', it is called the ''tortoise-shell turtle'', named primarily for its
shell which was used for decoration.
In
Japan, the turtles are also harvested for their shell
scutes, which are called ''bekko'' in the local
Nihongo. It is used in various personal implements, such as eyeglass frames. In 1994, Japan stopped importing hawksbill shells from other nations. Prior to this, the Japanese hawksbill shell trade was around 30,000 kilograms of raw shells per year.
[31][32] In the west, hawksbill turtle shells have been harvested by the
ancient Greeks and
ancient Romans for jewelry, such as combs, brushes and rings.
[33] A bulk of the world's hawksbill turtle shell trade is harvested from the Caribbean. In 2006, it was found that processed shells of the turtles are regularly available, often in large amounts in countries in the region, including the
Dominican Republic and
Colombia.
[34]
Conservation
General consensus has determined sea turtles, including ''Eretmochelys imbricata'' to be at the very least, threatened species because of their long lifespans, slow growth and maturity, and slow reproductive rates. Many adult turtles have been killed by humans both deliberately and incidentally. In addition, the nesting sites of the turtles are also threatened by human and animal encroachment. Small mammals have been known to raid the nesting sites and dig up the turtles' eggs.
In the
U.S. Virgin Islands, ''Eretmochelys imbricata'' nests (along with the nests of other sea turtles like ''
Dermochelys coriacea'') are often raided by
mongooses right after being laid.
[35]
In 1996, the
IUCN Red List of Threatened Species classified ''Eretmochelys imbricata'' as
critically endangered.
[36] Its status as an
endangered species was challenged prior to this, with two petitions claiming that the turtle (along with three other species) had several significant stable populations worldwide. These petitions were rejected by the IUCN based on their analysis of data submitted by the
Marine Turtle Specialist Group (MTSG). The data given by the MTSG showed that the worldwide population of hawksbill turtles had been reduced by 80% in the last three of the species' generations, and that was no significant increase in the turtles' populations as of 1996. In light of this data, the IUCN applied the ''critically endangered'' (A1) status upon the species. CR A2 status was denied however, because the IUCN believed that there was insufficient data to show that the population of hawksbill turtles were due to decrease by a further 80% in the future.
[37]
Historically, ''Eretmochelys imbricata'' was first listed as
endangered by the IUCN in 1982.
[38] This endangered status continued all the way through several reassessments in 1986,
[39] 1988,
[40] 1990
[41] and 1994
[42] until it was upgraded in status to ''critically endangered'' in 1996 (see above).
The species (along with the entire family '
Cheloniidae') has been listed on Appendix I of the
Convention on International Trade in Endangered Species.
[43] It is illegal to import or export turtle products, kill, capture or harass hawksbill turtles.
[44]
Local involvement in the conservation efforts for the species have also increased in the past few years. The
United States Fish and Wildlife Service has classified the hawksbill turtle as endangered since 1970. The U.S. government has several recovery plans in place for protecting its populations of ''E. imbricata''.
[45]
References
1.
2. Species Booklet: Hawksbill sea turtle
3. Hawksbill turtle - Eretmochelys imbricata: More information
4. Eretmochelys imbricata, Hawksbill Sea Turtle
5. The Hawksbill Turtle (''Eretmochelys imbricata'')
6. Hawksbill
7. The Hawksbill Turtle: Eretmochelys imbricata
8. Species Fact Sheet: ''Eretmochelys imbricata'' (Linnaeus, 1766)
9. Hawksbill Sea Turtle (''Eretmochelys imbricata'')
10. Turtles of the United States and Canada, , C. H., Pope, Alfred A. Knopf, ,
11. Sea Turtle Conservation along the Atlantic Coast of Africa, , Angela, Formia, Marine Turtle Newsletter,
12. Decline of the Nesting Population of Hawksbill Turtles at Tortuguero, Costa Rica, , Karen A., Bjorndal, Conservation Biology,
13. Origin of Hawksbill Turtles in a Caribbean Feeding Area as Indicated by Genetic Markers, , B. W., Bowen, Ecological Applications,
14. Uriel’s journey home — a Young pawikan’s story in Boracay Artem Colacion
15. Ocean Ambassadors - Philippine Turtle Islands
16. Nesting by the hawsbill turtle ''(Eretmochelys imbricata)'' on Milman Island, Great Barrier Reef, Australia, , K. A., Loop, Wildlife Research,
17. Nesting success of hawksbill turtles ''(Eretmochelys imbricata)'' on Cousine Island, Seychelles, , P. M., Hitchins, Journal of Zoology,
18. The Biology of Sea Turtles, , P. L., Lutz, CRC Press, ,
19. Habitat utilization by juvenile hawksbill turtles (''Eretmochelys imbricata'', Linnaeus, 1766) around a shallow water coral reef, , Jonathan D. R., Houghton, Journal of Natural History,
20. Spongivory in Hawksbill Turtles: A Diet of Glass, , Anne, Meylan, Science,
21. ADW: Eretmochelys imbricata: Information
22. Atlantic Hawksbill Sea Turtle Fact Sheet
23. A Molecular Phylogeny for Marine Turtles: Trait Mapping, Rate Assessment, and Conservation Relevance, , Brian W., Bowen, Proceedings of the National Academy of Sciences of the United States of America,
24.
25.
26.
27.
28.
29. Translations and Original Descriptions: Turtles
30. Eating Turtles in Ancient China, , Edward H., Schafer, Journal of the American Oriental Society,
31. Analysis of a Fisheries Model for Harvest of Hawksbill Sea Turtles (Eretmochelys imbricata), , Selina S., Heppel, Conservation Biology,
32. Tortoiseshell ban threatens Japanese tradition Gary Strieker
33. Periplus Maris Erythraei: Notes on the Text, , Lionel, Casson, The Journal of Hellenic Studies,
34. Turtles of the Caribbean: the curse of illegal trade
35. Mongoose Predation on Sea Turtle Eggs and Nests, , David W., Nellis, Biotropica,
36.
37. Ruling of the IUCN Red List Standards and Petitions Subcommittee on Petitions against the 1996 Listings of Four Marine Turtle Species, 18 October 2001 Red List Standards & Petitions Subcommittee
38. The IUCN Amphibia-Reptilia Red Data Book, Part 1: Testudines, Crocodylia, Rhynocehapalia, , B., Groombridge, IUCN, ,
39. 1986 IUCN Red List of Threatened Animals, IUCN Conservation Monitoring Centre, , , IUCN, ,
40. 1988 IUCN Red List of Threatened Animals, IUCN Conservation Monitoring Centre, , , IUCN, ,
41. 1990 IUCN Red List of Threatened Animals, IUCN, , , IUCN, ,
42. 1994 IUCN Red List of Threatened Animals, , B., Groombridge, IUCN, ,
43. Appendices CITES
44. Eretmochelys imbricata UNEP-WCMC
45. Species Profile: Hawksbill sea turtle (Eretmochelys imbricata)
See also
★ ''
Chelonioidea''. The
sea turtle superfamily.
★ ''
Caretta caretta''. The
loggerhead turtle.
★ ''
Chelonia mydas''. The
green turtle.
★ ''
Dermochelys coriacea''. The
leatherback turtle.
★ ''
Lepidochelys kempii''. The
Kemp's Ridley turtle.
★ ''
Lepidochelys olivacea''. The
olive ridley turtle.
★ ''
Natator depressus''. The
flatback turtle.
External links
★
Florida Sea Turtle information Florida Fish and Wildlife Conservation Commission
Fish and Wildlife Research Institute
★
WWF-Malaysia's Hawksbill Turtles Satellite Telemetry Website WWF-Malaysia's website featuring the journey of two satellite tracked hawksbill turtles and other information about hawksbill turtles in the region of Malacca, Malaysia.
★
Seaturtle.org Home to sea turtle conservation efforts such as the Marine Turtle Research Group and publisher of the Marine Turtle Newsletter.
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