Sea turtles, also called marine turtles, are air-breathing reptiles with streamlined bodies and large flippers. They are well-adapted to life in the marine environment. They inhabit tropical and subtropical ocean waters throughout the world. Although sea turtles live most of their lives in the ocean, adult females must return to beaches on land to lay their eggs. They often migrate long distances between feeding grounds and nesting beaches. Seven species of sea turtles have been identified worldwide. Six sea turtle species are found in U.S. waters (the flatback sea turtle is found only in Australia and Papua New Guinea). Five species of sea turtle occur in the Hawaiian waters, including green, hawksbill, leatherback, loggerhead and olive ridley sea turtles.

Green Sea Turtle (Chelonia mydas)

Green sea turtle
Green sea turtle.

The green sea turtle is the largest of all the hard-shelled sea turtles, with a comparatively small head. Hatchlings are about 2 in (50 mm) in length and weigh about 0.05 lb (25 g). Adults are about 3 ft (1 m) in length and weigh 300-350 lb (135-150 kg). The top shell (carapace) is smooth with shades of black, gray, green, brown, and yellow; the bottom shell (plastron) is yellowish-white. It is unknown how long they live, but sexual maturity occurs anywhere between 20-50 years.

The adult green turtle is unique among sea turtles because it’s an herbivore (eats only plants); feeding primarily on seagrasses and algae. This diet is thought to give them the greenish-colored fat from which they take their name.

Every 2-4 years, females return to the same beaches where they were born (natal beaches) to lay eggs. During the nesting season (generally in the summer months), females nest at approximately two-week intervals. They lay an average of five nests (clutches).

The green turtle is globally distributed and generally found in tropical and subtropical waters along continental coasts and islands between 30° N and 30° S latitude. Nesting occurs in over 80 countries throughout the year (though not throughout the year at each specific location). Green turtles are thought to inhabit coastal areas of more than 140 countries. More than 90% of the Hawaiian population of green turtles nests at French Frigate Shoals in the Northwestern Hawaiian Islands. They migrate to feed mainly in the coastal areas of the Main Hawaiian Islands. Limited nesting locations and important coastal foraging areas for green turtles are found throughout the Pacific islands.

Hawksbill Sea Turtle (Eretmochelys imbricata)

Hawksbill sea turtle
Hawksbill sea turtle.

The hawksbill sea turtle is unique among sea turtles because it has two pairs of prefrontal scales (between its eyes), and usually has two claws on each of its flippers. Its head is elongated and tapers to a point, with a beak-like mouth that gives the species its name. The shape of its mouth allows the hawksbill turtle to reach into holes and crevices of coral reefs to find invertebrates such as sponges, its primary food as an adult.

The hawksbill turtle is small to medium-sized compared to other sea turtle species. Hatchlings weigh around 0.5 oz (15 g), and are mostly brown. Adults are around 23-35 in (65-90 cm) long and weigh 100-150 lb (45-70 kg). The top shell (carapace) is dark- to golden-brown with streaks of orange, red, and/or black, a serrated back, and overlapping scutes (plates); while the bottom shell (plastron) is clear yellow.

It is unknown how long hawksbills live. Male hawksbills mature when they are about 27 in (70 cm) long; females mature at about 30 in (80 cm). The ages at which turtles reach these lengths are unknown. Every 2-3 years, females return to the beaches where they were born (natal beaches) to nest at night. They usually nest high up on the beach under or in vegetation. They commonly nest on pocket beaches with little or no sand. The nesting season varies geographically, but nesting usually occurs sometime between April and November. Nesting every 14-16 days, a female hawksbill sea turtle generally lays 3-5 nests per season, which contain an average of 130 eggs. Eggs incubate for around 2 months.

The hawksbill sea turtle is circumtropical, usually occurring from 30° N to 30° S latitude in the Atlantic, Pacific, and Indian Oceans and associated bodies of water. This species can be found nesting and foraging in Hawaii and other Pacific U.S. territories.

Leatherback Sea Turtle (Dermochelys coriacea)

Leatherback sea turtle
Leatherback sea turtle. Photo by Claudia Lombard/USFWS.

The leatherback is the largest sea turtle -- and one of the largest living reptiles -- in the world.

It is also the only sea turtle that doesn't have a hard bony shell. A leatherback's top shell (carapace) is about 1.5 in (4 cm) thick and consists of leathery, oil-saturated connective tissue overlaying loosely-interlocking dermal bones. Its carapace has seven longitudinal ridges and tapers to a blunt point, which help give it a more hydrodynamic structure. Hatchlings are 2-3 in (50-75 mm) in length and weigh around 1.5-2 oz (40-50 g). Adults are 6.5 ft (2 m) in length and can weigh up to 2000 lb (900 kg). Its shell is primarily black with pinkish-white coloring on their belly. Its lifespan is unknown.

The front flippers of a leatherback sea turtle don't have claws or scales and are proportionally longer than those of other sea turtles. Its back flippers are paddle-shaped. Both its ridged carapace and large flippers make the leatherback uniquely equipped for long-distance foraging migrations.

Females migrate to their respective nesting sites at 2- to 3-year intervals. They nest several times during a nesting season, typically at 8-12 day intervals, and lay clutches of approximately 100 eggs. After about two months, leatherback hatchlings emerge from the nest and have white striping along the ridges of their backs and on the margins of their flippers.

The leatherback sea turtle doesn't have the crushing chewing palates characteristic of other sea turtles that feed on hard-bodied prey. Instead, it has pointed tooth-like cusps and sharp-edged jaws that are perfectly adapted for a diet of soft-bodied pelagic (open ocean) prey, such as jellyfish and salps. A leatherback's mouth and throat also have backward-pointing spines that help retain such gelatinous prey. The leatherback sea turtle can dive to a depth of 4200 ft (1280 m) -- deeper than any other turtle -- and can stay under water for up to 85 minutes.

Leatherbacks have the widest global distribution of all reptiles. The leatherback sea turtle is distributed worldwide in tropical and temperate waters of the Atlantic, Pacific, and Indian Oceans. It is also found in small numbers as far north as British Columbia, Newfoundland, and the British Isles, and as far south as Australia, Cape of Good Hope, and Argentina.

Pacific leatherback sea turtles are genetically and biologically unique. They migrate extreme distances across the Pacific from nesting to foraging areas, and are generally larger than Atlantic leatherbacks. Pacific leatherbacks are split into two subpopulations -- Western and Eastern Pacific leatherbacks -- based on range distribution and biological and genetic characteristics. Western Pacific leatherbacks nest in the Indo-Pacific and migrate back to feeding areas off the Pacific coast of North America. Eastern Pacific leatherbacks nest along the Pacific coast of the Americas in Mexico and Costa Rica.

Loggerhead Sea Turtle (Caretta caretta)

Loggerhead sea turtle
A juvenile loggerhead sea turtle.

The loggerhead sea turtle was named for their relatively large heads, which support powerful jaws and enable them to feed on hard-shelled prey such as whelks and conch. The top shell (carapace) of adults and sub-adults is slightly heart-shaped and reddish-brown, while the bottom shell (plastron) is generally a pale, yellowish color. The neck and flippers are usually dull- to reddish-brown on top and medium- to pale-yellow on the sides and bottom. Hatchlings are 2 in (50 mm) in length and weigh around 0.05 lb (20 g). Adults are about 3 ft (1 m) in length and weigh about 250 lb (113 kg). Its lifespan is unknown, but the leatherback sea turtle reaches sexual maturity at around 35 years.

Females lay 3-5 nests, and sometimes more, during a single nesting season. The eggs incubate approximately two months before hatching. Hatchlings lack the reddish-brown coloration of adults and juveniles. Their flippers are dark gray to brown above with white to white-gray margins. The coloration of the plastron is generally yellowish to tan.

Loggerheads are circumglobal, occurring throughout the temperate and tropical regions of the Atlantic, Pacific, and Indian Oceans. Loggerhead sea turtles are the most abundant species of sea turtle found in U.S. coastal waters.

Olive Ridley Sea Turtle (Lepidochelys olivacea)

Olive ridley sea turtle
Olive ridley sea turtle. Photo by Bernard Gagnon.

The olive ridley is considered the most abundant sea turtle in the world, with an estimated 800,000 females nesting annually. The olive ridley gets its name from the olive (or olive/grayish-green) coloration of its heart-shaped top shell (carapace). Hatchlings emerge mostly black with a greenish hue on their sides, are 1.5 in (40 mm) in length, and weigh less than 1 oz (28 g). Adults are 22-31 in (55-80 cm) long and weigh around 100 lb (45 kg). Their lifespan is unknown, but they reach sexual maturity at about 15 years. Their diet consists of algae, lobster, crabs, tunicates, mollusks, shrimp, and fish.

The olive ridley sea turtle is relatively small. Its size and morphology varies from region to region, with the largest animals observed on the Pacific coast of Mexico. There are often only 5 pairs of costal scutes (plates) on its carapace, but that number varies. Some individuals have been documented having as many as 9 pairs of costal scutes. Each of their four flippers has 1-2 visible claws. The carapace of the eastern Pacific olive ridley is taller than the carapace of olive ridley in other populations, and are usually lighter in color than western Atlantic olive ridleys’.

The olive ridley has one of the most extraordinary nesting habits in the natural world. Large groups of turtles gather off shore of nesting beaches. Then, all at once, vast numbers of turtles come ashore and nest in what is known as an "arribada." During these arribadas, hundreds to thousands of females come ashore to lay their eggs. At many nesting beaches, the nesting density is so high that previously-laid egg clutches are dug up by other females excavating the nest to lay their own eggs.

The olive ridley is globally distributed in the tropical regions of the South Atlantic, Pacific, and Indian Oceans. In the South Atlantic Ocean, they are found along the Atlantic coasts of West Africa and South America. In the eastern Pacific, they occur from southern California to northern Chile. The Pacific nesting grounds include the Pacific coasts of Mexico and Central America. The turtle does not nest anywhere under U.S. jurisdiction in the Pacific Islands region; however, the olive ridley sea turtle is encountered in U.S. waters as it travels between nesting and foraging grounds.

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