The Hawksbill Turtle

10:25 PM


The Hawksbill sea turtle (Eretmochelys imbricata) is a critically endangered sea turtle belonging to the family Cheloniidae. The hawksbill's appearance is similar to that of other marine turtles. It has a generally flattened body shape, a protective carapace, and flipper-like arms, 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.


The hawksbill is one of the smaller sea turtles. Head is narrow and has 2 pairs of prefrontal scales (scales in front of its eyes). Jaw is not serrated. Carapace is bony without ridges and has large, over-lapping scutes (scales) present and has 4 lateral scutes. Carapace is elliptical in shape. Flippers have 2 claws. The carapace is orange, brown or yellow and hatchlings are mostly brown with pale blotches on scutes.

Relative Size

            Not particularly large compared with other sea turtles, the adult hawksbill sea turtles have been known to grow up to 1 m (3 ft.) in length, weighing around 80 kg (180 lb.) on average. The heaviest hawksbill ever captured was measured to be 127 kg (280 lb.).


Did You Know

Young hawksbill turtles are unable to dive deep and spend their early years floating amongst sea plants near the water’s surface. 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.


Scientific Classification

Kingdom
Animalia
Phylum
Chordata
Class
Reptilia
Order
Testudines
Family
Cheloniidae
Genus
Eretmochelys
Species
imbricata

Other Names

German
Echte Karettschildkröte
French
Tortue imbriquée
Spanish
Tortuga carey
  
Status

The hawksbill turtle is classified as Critically Endangered (CR) on the IUCN Red List, and is listed on Appendix I of CITES, and Appendix I of the Convention on Migratory Species (CMS or Bonn Convention). The United States Fish and Wildlife Service and National Marine Fisheries Service have classified hawksbills as endangered under the Endangered Species Act since 1970.


Population

Hawksbills are solitary nesters and, thus, determining population trends or estimates on nesting beaches is difficult. The largest populations of hawksbills are found in the Caribbean, the Republic of Seychelles, Indonesia, and Australia. Each year, about 500-1000 hawksbill nests are laid on Mona Island, Puerto Rico and another 100-150 nests on Buck Island Reef National Monument off St. Croix in the U.S. Virgin Islands. In Mexico, about 2,800 hawksbills nest in Campeche, Yucatán, and Quintana Roo each year. Lutz et al. estimate the number of adult hawksbills living in the Caribbean today is 27,000.


The largest nesting population of hawksbills appears to occur in Australia. Approximately 2,000 hawksbills nest on the northwest coast of Australia and about 6,000 to 8,000 off the Great Barrier Reef each year. Additionally, about 2,000 hawksbills nest each year in Indonesia and 1,000 in the Republic of Seychelles.

Habitat

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. 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.


Range

          The Hawksbill sea turtles have a wide range, found predominantly in tropical reefs of the Indian, Pacific, and Atlantic Oceans. They have a circum-global distribution throughout tropical and, to a lesser extent, subtropical waters of the Atlantic Ocean, Indian Ocean, and Pacific Ocean. Hawksbills are migratory and individuals undertake complex movements through geographically disparate habitats during their lifetimes.


Biology

Hawksbills are omnivorous and will also eat mollusks, marine algae, crustaceans, sea urchins, fish, and jellyfish. They feed mainly on sponges by using their narrow pointed beaks to extract them from crevices on the reef, but also eat sea anemones and jellyfish. In the Caribbean, as hawksbills grow, they begin exclusively feeding on only a few types of sponges, and they can eat an average of 1200 lb. (544 kg) of sponges a year. Aside from sponges, hawksbills feed on algae, cnidarians, comb jellies and other jellyfish, and sea anemones. They also feed on the dangerous jellyfish-like hydrozoan, the Portuguese man o' war.


Male hawksbills mature when they are about 27 inches (70 cm) long. Females mature at about 30 inches (80 cm). The ages at which turtles reach these lengths are unknown (They reach maturity after 30 years.). Female hawksbills return to the beaches at night, where they were born (natal beaches) every 2-3 years to nest. They usually nest high up on the beach under or in the beach/dune vegetation. The nesting season varies with locality, but in most locations nesting occurs sometime between April and November. A female hawksbill generally lays 3-5 nests per season, which contain an average of 130 eggs. Eggs incubate for around 2 months.


The baby turtles usually hatch at night after around two months. 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. The normal lifespan of hawksbill turtles is thought to be about 30 to 50 years.


Predators

Hawksbill turtles have a hard shell that discourages predators from trying to eat them. Adult turtles are consumed by sharks, crocodiles, large fish, and octopi. 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.
  

Threats

The most important threats to Hawksbill turtles are

(i) Tortoiseshell Trade - Within the last 100 years, millions of Hawksbills have been killed for the tortoiseshell markets of Europe, the United States and Asia. The global plight of the Hawksbill in the latter half of the 20th Century has been recognized by the inclusion of the species in the most threatened category of IUCN’s Red List since 1968 and the listing of all Hawksbill populations on Appendix I of CITES, the Convention on International Trade in Endangered Species, since 1977. 
(ii) Egg Collection - Intense levels of egg exploitation continue in many parts of the world, especially Southeast Asia, where it approaches 100% in many areas. 
(iii) Destruction of Nesting Habitat - Tropical coastlines are rapidly being developed for tourism which often leads to destruction of nesting habitat. Because Hawksbills prefer to nest under vegetation they are particularly impacted by beach-front development and clearing of dune vegetation. 
(iv) Destruction of Foraging Habitat - Hawksbills are typically associated with coral reefs, which are among the world’s most endangered marine ecosystems. Climate change has led to massive coral bleaching events with permanent consequences for local habitats. 
(v) Entanglement and Ingestion of Marine Debris - including Fishing Gear. Hawksbills are particularly susceptible to entanglement in gill nets and capture on fishing hooks.


Conservation Measures

           In 1982, the IUCN Red List of Threatened Species first listed E. imbricata as endangered. This endangered status continued through several reassessments in 1986, 1988, 1990 and 1994 until it was upgraded in status to critically endanger in 1996. The data given by the MTSG (Marine Turtle Specialist Group) 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.


Hawksbill turtles are protected by various international treaties and agreements as well as national laws. They are listed in Appendix I of the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES), which means that international trade of this species is prohibited. In the U.S., NOAA Fisheries and the U.S. Fish and Wildlife Service (USFWS) have joint jurisdiction for marine turtles, with NOAA having the lead in the marine environment and USFWS having the lead on the nesting beaches. Both federal agencies, and a number of state agencies, have promulgated regulations to eliminate or reduce threats to sea turtles.
  

References
http://www.seaturtles911.org/image/hatchling-predators.jpg


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