Hawksbill Sea Turtles, Eretmochelys imbricata
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Description & Behavior
Hawksbill sea turtles, Eretmochelys imbricata (Linnaeus, 1766), are beautiful small to medium-sized sea turtles that take their species name (imbricata) from the overlapping plates on their upper shell. Hawksbills get their common name from the shape of its hooked jaw. They reach a length of about 0.62-1.14 m.
In the U.S. Caribbean, nesting females average about 0.62-0.94 m in straight carapace length. Weight is typically to 80 kg in the wider Caribbean, with a record weight of 127 kg. Hatchlings average about 42 mm straight carapace length and range in weight from 13.5-19.5 g. The following characteristics distinguish the hawksbill from other sea turtles: two pairs of prefrontal scales; thick, posteriorly overlapping scutes (plates) on the carapace; four pairs of coastal scutes; two claws on each flipper; and a beak-like mouth. The carapace is heart-shaped in very young turtles, and becomes more elongate or subovate with maturity.
Its lateral and posterior margins are sharply serrated in all but very old individuals. The epidermal scutes that overlay the bones of the shell are the shells sold commercially. They are unusually thick and overlap posteriorly on the carapace in all but hatchlings and very old individuals. Carpacial scutes are often richly patterned with irregularly radiating streaks of brown or black on an amber background. The scutes of the plastron of Atlantic hawksbills are usually clear yellow, with little or no dark pigmentation. The soft skin on the ventral side is cream or yellow and may be pinkish-orange in mature individuals. The scales of the head and forelimbs are dark brown or black with sharply defined yellow borders. There are typically four pairs of inframarginal scales. The head is elongate and tapers sharply to a point. The lower jaw is V-shaped.
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.
Male turtles are distinguished by a brighter pigmentation, a concave plastron, long claws and a thicker tail.
Sea turtles are some of the largest turtles in the world and live in almost every ocean of the world. Their smooth shells and paddlelike flippers help them speed through the water as fast as 24 kph. These long-distance travelers have been known to swim up to 4,828 km.
Although sea turtles cannot withdraw their heads into their shells, the adults are protected from predators by their shells, large size and thick scaly skin on their heads and necks.
Sea turtles spend almost all their lives submerged but must breathe air for the oxygen needed to meet the demands of vigorous activity. With a single explosive exhalation and rapid inhalation, sea turtles can quickly replace the air in their lungs. The lungs are adapted to permit a rapid exchange of oxygen and to prevent gasses from being trapped during deep dives. The blood of sea turtles can deliver oxygen efficiently to body tissues even at the pressures encountered during diving. During routine activity green and loggerhead turtles dive for about 4 to 5 minutes and surface to breathe for 1 to 3 seconds. A female loggerhead tracked at sea made up to 500 dives every 12 hours.
Sea turtles can rest or sleep underwater for several hours at a time but submergence time is much shorter while diving for food or to escape predators. Breath-holding ability is affected by activity and stress, which is why turtles drown in shrimp trawls and other fishing gear within a relatively short time.
Because sea turtles are difficult to study in the open ocean, scientists are just beginning to learn about the life history of sea turtles. Today, radio transmitters, attached to nesting turtles, help track the sea creatures on their travels and provide valuable information.
World Range & Habitat
Eretmochelys imbricata, or hawksbill sea turtles, are found mainly in the tropical regions of the Atlantic and Pacific oceans. In the western hemisphere, they have been reported to have nests as far north as Woods Hole, Massachusetts and are also present in the Long Island Sound. However, between the Carolinas and New Jersey, very few hawksbill turtles have been recorded.
Also found around the Oceanic Islands and Indian Ocean. Hawksbill turtles are most commonly found in coral reef habitats where sponges, a food source for hawksbills, grow on solid substrate. They also reside in shoals, lagoons of oceanic islands and on continental shelves. They are most commonly found in water 18.3 m or shallower. The habitats of hawksbills vary by stages in their life cycle. Young hawksbill turtles cannot dive into deep water and therefore live on masses of floating sea plants, such as sargassum. Hawksbills re-enter coastal waters when they reach approximately 20-25 cm carapace length. The ledges and caves of the reef provide shelter for resting both during the day and night. Hawksbills are also found around rocky outcrops and high energy shoals, which are also optimum sites for sponge growth. In areas where there are no coral reefs, hawksbills are found in mangrove-fringed bays and estuaries. In Texas, juvenile hawksbills are also found near stone jetties.
Feeding Behavior (Ecology)
Hawksbill sea turtles are omnivorous with a diet that consists primarily of sponges. They are selective feeders choosing only certain species of sponges of which are toxic to other animals. Sea jellies and other coelenterates are also common prey for hawksbill turtles. They also eat mollusks, fish, marine algae, crustaceans and other sea plants and animals. A preferred feeding ground of the hawksbills is in shallow shoals abundant with brown algae.
The actual age that hawksbill sea turtles reach sexual maturity is unknown. Mating occurs roughly every 2-3 years mainly in shallow waters. Copulation usually begins near the shore. Hawksbills leave the water only during the breeding season when females dig nests in the sand, typically near vegetation. The entire nesting process takes 1-3 hours. They clear the area and dig a pit in the sand. They lay their eggs in the pit then fill it with sand using their hind limbs. After the eggs are laid and buried, they immediately return to the sea.
After about two months, the hatchling turtles emerge at night. The light reflected off the water from the sky guides them to the sea. These days, car headlights, street lamps, or lights on buildings near the beach cause some hatchlings to travel in the wrong direction. Waiting herons make fast meals of other hatchlings. Any babies still on the beach in the morning are easily picked off by predators or die in the hot sun. It is thought that when the surviving hatchlings reach maturity, they return to the beach where they hatched to lay their eggs.
Like all turtles, the hard carapace of hawksbills discourages predators. Adult turtles are still consumed by humans, sharks and occasionally crocodiles. Nests are commonly robbed by terrestrial predators such as dogs, raccoons, rats, mongooses and humans. Directly after hatching, hawksbill turtles make the journey to water. Although this trip only takes a few minutes, many hatchlings are preyed upon by various gulls, herons and large crabs.
Conservation Status & Comments
The eggs of hawksbill sea turtles were once a popular food for humans as was the meat, however the sale and consumption of turtle eggs is now illegal and the meat was found to be frequently poisonous to humans. The skin of these turtles is also toxic to humans. The sale of hawksbill turtle shells is also illegal.
WARNING: Eating sea turtles and their eggs, anywhere, can cause severe illness and even death, especially to children. The flesh has been found to contain chelonitoxin which may cause a number of symptoms including nausea, vomiting, diarrhea, burning sensation of lips, tongue and mouth, chest tightness, difficulty swallowing, hypersalivation, skin rash, coma and death. See the following for more information:
Chelonitoxism: new case reports in French Polynesia and review of the literature
Turtle meat kills six in Micronesia
More than 50% of sea turtle eggs are stolen by humans, which has lead to a decrease in turtle populations worldwide which face a serious threat of extinction. A status that has not changed since 1970. As of 1983, the only known stable populations of hawksbills were found in the middle east and northeastern Australia. Commercial exploitation to meet the demand for the hawksbill's shell which commands as much as $225/kg, remains a major obstacle to hawksbill protection. Hawksbill "leather" is also sold as well as its oil which is used for some perfume and cosmetics. Japan imported about 20 metric tons of hawksbill shell per year from approximately 19,000 turtles until a settlement was negotiated on this trade in 1992.
Hawksbill sea turtles, Eretmochelys imbricata, are listed as Critically Endangered (CR A1bd) on the IUCN Red List of Threatened Species:
CRITICALLY ENDANGERED (CR)
A taxon is Critically Endangered when it is facing an extremely high risk of extinction in the wild in the immediate future, as defined by any of the criteria (A to E) as described here.
References & Further Research
Hawksbill Sea Turtle Recovery - U. S. Fish and Wildlife Service resources for information on the Hawksbill sea turtle and its recovery.
Hawksbill Turtle - NOAA Fisheries
Photos: David Hall's Encounters in the Sea
Fish and Wildlife Service Sea Turtle Information
Turtle Trax - A Marine Turtle Page
Caribbean Conservation corporation/Sea Turtle Survival League
Archie Carr Center for Sea turtle Research and Sea Turtle on-line Bibliography
U.S. Fish & Wildlife Service Endangered Species
The State of the World's Sea Turtles (SWoT)
IUCN/SSC Marine Turtle Specialist Group
IUCN Red List of Threatened Species
Research Eretmochelys imbricata » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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