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Gregory R. Mann, Ph.D. {ret.}

Hawksbill Sea Turtle

“Eretmochelys imbricata”

Hawksbill Sea Turtles are beautiful small to medium-sized sea turtles that take their species name 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 meters. In the U.S. Caribbean, nesting females average about 0.62-0.94 meters in straight carapace length. Weight is typically to 80 kilograms in the wider Caribbean, with a record weight of 127 kilograms. Hatchlings average about 42 millimeters straight carapace length and range in weight from 13.5-19.5 grams. 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. Hawksbill 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 Hawksbill Sea Turtles are difficult to study in the open ocean, scientists are just beginning to learn about their life history. Today, radio transmitters attached to nesting turtles, help track the sea creatures on their travels and provide valuable information. 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 Sea Turtles have been recorded.

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 Hawksbill Sea Turtle 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. Hawksbill Sea Turtles 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. Males are distinguished by a brighter pigmentation, a concave plastron, long claws and a thicker tail.

Hawksbill Sea Turtles are some of the largest turtles in the world and live in almost every ocean of the world. Their smooth shells and paddle-like flippers help them speed through the water as fast as 24 kph. These long-distance travelers have been known to swim up to 4,428 kilometers. Although Hawksbill 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. Hawksbill 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. Their lungs are adapted to permit a rapid exchange of oxygen and to prevent gasses from being trapped during deep dives. The blood of Hawksbill Sea Turtles can deliver oxygen efficiently to body tissues even at the pressures encountered during diving. 

Also found around the Oceanic Islands and Indian Ocean, Hawksbill Sea 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 meters or shallower. The habitats of Hawksbill Sea Turtles vary by stages in their life cycle. Young Hawksbill Sea 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 centimeters carapace length. The ledges and caves of the reef provide shelter for resting both during the day and night. Hawksbill Sea Turtles 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 Hawksbill Sea Turtles are also found near stone jetties.

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 Sea 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 2 months, the hatchling Hawksbill Sea 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 Hawksbill Sea Turtles discourages predators. Adult turtles are still consumed by humans, sharks and occasionally Salt Water Crocodiles. Nests are commonly robbed by terrestrial predators such as dogs, raccoons, rats, mongooses and humans. Directly after hatching, Hawksbill Sea 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.

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