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Eretmochelys imbricataHawksbill

By Michael Edelman

Geographic Range

Eretmochelys 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. (Lutz and Musick, 1997; Pope, 1939)

Habitat

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. (Lutz and Musick, 1997; Pope, 1939)

  • Aquatic Biomes
  • reef
  • Range depth
    20 to 0 m
    65.62 to 0.00 ft
  • Average depth
    Near Surface m
    ft

Physical Description

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. (Ernst, et al., 1994; "The Hawksbill Turtle (Eretmochelys imbricata)", 1999)

Eretmochelys 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. (Ernst, et al., 1994; "The Hawksbill Turtle (Eretmochelys imbricata)", 1999)

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 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. ("The Hawksbill Turtle (Eretmochelys imbricata)", 1999)

  • Sexual Dimorphism
  • male more colorful
  • sexes shaped differently
  • Range mass
    35.7 to 127 kg
    78.63 to 279.74 lb
  • Average mass
    80 kg
    176.21 lb
  • Range length
    62.5 to 114 cm
    24.61 to 44.88 in
  • Average length
    87 cm
    34.25 in

Development

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. ("The Hawksbill Turtle (Eretmochelys imbricata)", 1999)

  • Development - Life Cycle
  • temperature sex determination

Reproduction

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. (Pope, 1939)

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. (Pope, 1939)

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. (Ernst, et al., 1994)

  • 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
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    1277 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    1277 days
    AnAge

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. ("Atlantic Hawksbill Sea Turtle Fact Sheet", 2003)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

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. ("Atlantic Hawksbill Sea Turtle Fact Sheet", 2003)

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

Behavior

Hawksbill turtles were once thought to have remained in one local area for the duration of their lives. However, recent studies have proven that they migrate very long distances during their lifetimes.

Typically diurnal (except during mating season), solitary hawksbill turtles comb the reefs and continental shelves searching for food. (Ernst, et al., 1994)

Communication and Perception

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. (Ernst, et al., 1994)

Food Habits

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. (Ernst, et al., 1994; Pope, 1939)

  • 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

Predation

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. (Bjorndal, 1999; Ernst, et al., 1994)

Ecosystem Roles

Hawksbill turtles often times feed on sponges, causing succession to occur in the reef and freeing up space for settlement of other organisms. ("The Hawksbill Turtle (Eretmochelys imbricata)", 1999)

  • Ecosystem Impact
  • creates habitat

Economic Importance for Humans: Positive

For years, humans have hunted the hawksbill turtles in order to sell their scutes. Also, humans eat the turtles as well as their eggs. (Bjorndal, 1999)

  • Positive Impacts
  • food
  • body parts are source of valuable material

Economic Importance for Humans: Negative

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

Conservation Status

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. (Bjorndal, 1999)

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. (Bjorndal, 1999)

Contributors

Matthew Wund (editor), University of Michigan-Ann Arbor.

Michael Edelman (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

food

A substance that provides both nutrients and energy to a living thing.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

macroalgae

seaweed. Algae that are large and photosynthetic.

magnetic

(as perception channel keyword). This animal has a special ability to detect the Earth's magnetic fields.

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

visual

uses sight to communicate

References

New York State Department of Environmental Conservation. 2003. "Atlantic Hawksbill Sea Turtle Fact Sheet" (On-line ). Accessed 03/21/03 at http://www.dec.state.ny.us/website/dfwmr/wildlife/endspec/athafs.html.

World Wildlife Foundation. "Hawksbill Turtle" (On-line ). Accessed 03/21/03 at http://www.wwfguianas.org/hawksbill.htm.

Turtle Trax. 1999. "The Hawksbill Turtle (Eretmochelys imbricata)" (On-line ). Accessed 03/16/03 at http://www.turtles.org/hawksd.htm.

Bjorndal, K. A. 1999. Conservation of Hawksbill Sea Turtles: Perceptions and Realities". Accessed 03/16/03 at http://www.turtles.org/bjorndal.htm.

Ernst, C., J. Lovich, R. Barbour. 1994. Turtles of the United States and Canada. Washington and London: Smithsonian Institution Press.

Lutz, P. L., J. A. Musick. 1997. The Biology of Sea Turtles. Boca Raton, Florida: CRC Press.

Pope, C. H. 1939. Turtles of the United States & Canada. New York: Alfred A Knopf.

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