Sea Turtles

Description

Sea turtles have been around for over 150 million years, before the time of the dinosaurs. Since the time when dinosaurs roamed the earth, sea turtles have remained virtually unchanged. For many indigenous people, these magnificent creatures represent creation, longevity, and wisdom.

There are 220 species of living turtles, but only seven of them live in the ocean. The species are the Green, Hawksbill, Leatherback, Loggerhead, Kemp’s Ridley, Olive Ridely, and Australian Flatback sea turtle. All seven species are either endangered or threatened, primarily due to human activities.

Sea turtles are reptiles. Reptiles are cold-blooded and breathe air. Like all turtles, sea turtles have an outer shell. The top part of the shell is called the “carapace,” and the bottom part of the shell is called the “plastron.” The shell is made up of large bones that are covered by large scales called “scutes.” Different species have different numbers, shapes, and distribution of scutes. The sea turtle’s head also has scutes on it. The Leatherback sea turtle, however, has no scutes. The front limbs of the sea turtle are shaped into flippers, while the back limbs are more like paddles with a membrane joining all five toes.

Males and females can only be differentiated when they become adults. The adult male has a long, thick tail extending almost to the hind limbs. Males also possess a long, heavy claw used to cling to the female during mating. Adult females have a much shorter tail and shorter, thinner claws. The Leatherbacks, however, do not possess a claw.

The three native Hawaiian species include the Green and Hawksbill sea turtles, which nest on Hawaii’s beaches, and the Leatherback, found in Hawaii’s offshore waters.

By monitoring the health of our turtles, we can monitor the health of our environment.

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Range and Habitat

Sea turtles can be found in warm and temperate seas throughout the world. Most sea turtles spend their adulthood in shallow, coastal waters, bays, lagoons, and estuaries, but some spend the majority of their life in the open ocean.

Loggerhead, Green, Leatherback, Kemp’s Ridley, and Hawksbill sea turtles regularly nest on beaches within the U.S., and all species depend on U.S. coastal waters for foraging. The Olive Ridely sea turtle does not nest in the U.S., but frequents U.S. waters during feeding migrations. The Loggerhead has the longest and most complex migration of all sea turtles, stretching across the Pacific from Mexico to Japan.

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Behavior

The sea turtle spends most of their time in the sea, unlike the land turtles from which they evolved. Generally, females only come back to the beach for nesting, and males never return to the beach. In rare areas, sea turtles will come out onto the beach to rest.

While at sea, they can remain underwater for several hours without taking a breath.

Sea turtle hearing is sensitive to low frequency sounds and vibrations. They have good eyesight under water, but are shortsighted in the air. The soft parts of their flippers and their shell are sensitive to touch. Many researchers believe they have an acute sense of smell and taste that helps them locate food.

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Reproduction

During the breeding season, sexually mature males and females can migrate thousands of miles to the breeding grounds near the nesting sites. The males will arrive first, early in the breeding season, and are the first to return to the feeding grounds. Females will remain in the coastal waters near their nesting beaches between nestings. Nesting begins when the female makes her way up the beach, usually at nighttime, and digs a large hole in the sand with her front flippers. After about ten minutes, she will begin digging with her hind legs to excavate the egg chamber. There she will lay more than a hundred leathery-shelled eggs, each about the size of a ping-pong ball. After laying her eggs, she will cover the eggs with sand and return to the ocean. This process may be completed in only 30 minutes. Once nesting is complete, she will ovulate once again, shedding another 100 eggs from her ovaries into her oviducts. These eggs become fertilized and get covered with albumin and shells. After two weeks, she will be ready to lay her next clutch of eggs. Females may lay several clutches of eggs prior to returning to their feeding grounds.

The eggs incubate in the warm sand and will hatch in about two months. Eggs exposed to higher temperatures will develop as females. Once hatched, the turtles dig their way to the surface and scurry to the ocean. It is believed by some that imprinting on the earth’s magnetic field may occur upon their emergence from the sand. This imprinting is believed to guide the hatchlings back to the same breeding areas at adulthood. If the hatchlings reach the ocean successfully, they will spend the next several years dispersing in ocean currents; they will associate with sargassum rafts and floating debris, which provide them with food and shelter.

Young sea turtles may move back into shallow coastal waters, feeding principally on bottom-living organisms. Loggerheads, however, remain in the open ocean for many years. Sexual maturity may be as long as 30-50 years for Green and Loggerhead sea turtles. At this time, it is believed they will return to the beaches where they hatched. Following the breeding season, they will return to the feeding grounds from which they migrated. The males may breed every one to two years, while females will migrate on an average of every two to five years.

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Food and Foraging

Sea turtles can be carnivorous (meat-eating), herbivorous (plant-eating), or omnivorous (eating both meat and plants). The meat they eat includes crabs, mollusks, shrimps, tunicates, squids, cuttlefish, sea cucumbers, and jellyfish. Plants include coral, sponges, and sea grasses. The structure of their jaw is usually indicative of their diet. In some species such as Green sea turtles, their eating habits change as they age. They switch from a carnivorous diet to a herbivorous one.

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Status and Conservation

In the past century, all seven species of sea turtles are at an increasing risk of becoming extinct. Primary threats include: the destruction of coral reefs, loss of nesting beaches due to human development, ocean pollution, harvesting them for their shells, leather, meat, and eggs, entanglement in driftnets, gillnets, shrimp trawling nets, and disease such as fibropapilloma. Hawksbills were especially recognized for their beautiful shell and often exploited for jewelry.

Kemps Ridley sea turtles are considered the most endangered. There nesting site was a mystery until 1947, when a Mexican architect (Ing. Herrera) filmed over 40,000 females nesting on two neighboring beaches in Mexico. This annual event is known as an arribada. Less than 4,000 females nest at these beaches today.

Fortunately, many sea turtles are protected under international treaties and national laws. National Marine Fisheries Service (NMFS) and the Fish and Wildlife Service (FWS) share Federal jurisdiction over their protection. NMFS oversees the marine environment, while FWS monitors the nesting beaches. However, because all sea turtles share international waters, it is imperative that conservation efforts involve cooperation among all nations to ensure their continued survival.

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