SEA TURTLES, CHARACTERISTICS, NESTING SITES, HATCHLINGS AND CONSERVATION

SEA TURTLES

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Green turtle in Hawaii
Turtles are reptiles. The are cold blooded and lay eggs and have been the around for around 200 million years. Sea turtles date back to the time of the dinosaurs and have not changed that much since then. They evolved from air-breathing land-dwelling tortoises. There 250 species of turtles. They live on land and in salt water and fresh water. Eight species live in the sea. Males can be distinguished from females by their longer tails. Some can live to be over a 100 years old. [Source: Anne and Jack Rudloe, National Geographic, February 1994]

Seas turtles can not breath underwater. Like dolphins and whales they have to surface from time to time to breath. Turtles can not breath like human by expanding and contracting the rid cage. Instead they rely on muscles around their lungs to do the job. Sea turtles mostly cruise at a leisurely pace but are capable of moving a great speeds with legs that have been modified into long, broad flippers. Some sea turtles can dive to a depth of 1,000 meters.

Turtles often rest under ledges at night. Sometimes they become disoriented trying to return to the surface and drown. They are preyed up by large sharks. Some sea turtles have scars on their shells and chunks from limbs missing as a result of shark attacks. The populations of sea turtles are estimated by counting the number of turtles at hatching sights.

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hawksbill turtle
Websites and Resources: National Oceanic and Atmospheric Administration noaa.gov/ocean ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Ocean World oceanworld.tamu.edu ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Montery Bay Aquarium montereybayaquarium.org

Websites and Resources on Fish and Marine Life: MarineBio marinebio.org/oceans/creatures ; Census of Marine Life coml.org/image-gallery ; Marine Life Images marinelifeimages.com/photostore/index ; Marine Species Gallery scuba-equipment-usa.com/marine

Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) coris.noaa.gov ; International Coral Reef Initiative icriforum.org ; Wikipedia article Wikipedia ; Coral Reef Alliance coral.org ; Global Coral reef Alliance globalcoral.org ; Coral Reef Pictures squidoo.com/coral-reef-pictures ; The Global Coral Reef Monitoring Network; the International Coral Reef Action Network.

Website: Turtle restoration Project: www.seaturtles.org

Turtles and Tortoises

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Turtles and tortoises are reptiles with shells. Turtles live mostly in the water and tortoises live mostly on land. According to the official Red List by the World Conservation Union almost half the turtles and tortoises are threatened.

Freshwater turtles are common sites in ponds, lakes, rivers and streams. They are commonly seen sunning themselves on rocks and logs. During the winter in temperate areas turtles hibernate by spending months in the mud without taking a breath.

The males and females of many turtles species bob their heads up and own, sometimes for hours, before mating. The males of some species bite the females head and suck on her feet to get her in the mood. During copulation the male often bites into the shell of the female to steady himself. Some males have to prop themselves up in an almost vertical position on the female to achieve penetration.

Origin of Turtles

Oliver Rieppel, curator of fossil reptiles at the Field Museum in Chicago, told the Chicago Tribune, “The origin of the turtle shell has been a big debate in paleontology for a long time. The turtle shell is such a specialized, unique feature. No other vertebrate animal group has this kind of body plan that has always been a big mystery.”

It appears that turtles first had shells only on their bellies. In an article in Nature in November 2008, Rieppel described a fossil — found in what used to be a shallow sea in Guizhou Province of southwestern China — of a turtle that lived 220 million years ago, a time when dinosaurs first appeared. The toothy aquatic creature — named “Odontochelys semitestacea”Latin for “half-shelled turtle with teeth”) was about 40 centimeters long and had a shell on its belly (a plastron) but lacked one on its back (the carapace). Its ribs and backbones were beginning to expand and grow together in such a way that millions of year larger would yield a carapace.

Some scientist dispute the conclusion. Robert Reisz, an evolutionary biologist at the University of Toronto, said he thinks Odontochelys once had a carapace and lost as an adaption to its environment the same ways some modern sea turtles have.

The oldest previously known turtle fossil has a full shell, beaked mouth and no teeth like modern turtles. It was would found in Germany and dated to about 206 million years ago.

Turtle Characteristics

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green turtle
Turtles don't have teeth. They chew and grasp things with horny jaws that contain sharp, almost knifelike cutting edges. Some turtles are completely vegetarian. Others are completely carnivorous. Many are omnivorous, eating whatever they can find. Turtles can not breath like human by expanding and contracting the rid cage. Instead they rely on muscles around their lungs to do the job.

Turtle shells consist of two parts: 1) the carapace, the upper, arched part; and 2) the plastron, the flat lower part. The carapace is attached to the backbone and ribs. The palstron is fused to the breastbone. In hard shelled turtles the bone is covered by a shield made of a horn-like material. Soft shelled turtles have a covering of tough skin over the bony shell.

The carapace consists of two layers: an inner core of bony plates that are fused together, and an outer layers of shields made of hornlike keratin, called scutes. The shape and patterns of the scutes is a useful clue in identifying different species.

A turtle's shell grows along with the animal and, unlike the skin of lizards and snakes, is not periodically shed. Most turtles when flipped on their back can turn themselves back over.

Reptile Characteristics

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Turtles are reptiles. Reptiles have a distinctive hearts with three chambers — two rear chambers (auricles) and one front chamber (ventricle) — with a partition that divides the heart almost completely in two. By contrast mammals have a four-chambered heart and amphibians have a three-chambered heart without a partition.

Reptiles swallow rather than chew their food. Many have jaw bones that bend and pivot and even come unhinged to allow the reptile to manipulate large prey. These developments freed the tongue from manipulating prey and allowed it become a sense organ . The forked tongue that many snakes and reptiles possess dates back to around 65 million years ago. It picks up chemical clues in “stereo” which allows reptiles to locate things.

Cold Blooded Reptiles

Reptiles are ectothermic (cold blooded), which means they can not regulate their body temperature internally and can not create heat with their bodies like mammals can and are at the mercy of the sun and their surroundings for heat. This explains why reptiles are less common in cold and temperate areas.

Because they are cold blooded, reptiles can move vigorously when the weather is hot but are sluggish and move slowly when it is cool. At night a reptile’s body heat falls with dropping temperature of its surroundings.

Being cold blooded has its advantages. Because reptiles receive much of their energy from outside their bodies and do not have to create it, they are more energy efficient and need less food. This and the fact they have salt-excreting glands also means that they are more tolerant to salt, and thus are capable of surviving long periods at sea, which explains how they have traveled across seas and inhabited islands that no mammal, until the arrival of man, could ever make it to.

Reptile Reproduction

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Baby Sea turtle
Reptiles were the first creatures to develop eggs. They passed on the ability to birds. Today, most reptiles lay eggs but not all of them. Boa constrictors, rattlesnakes and chameleons give birth to live young while pythons, cobras and iguanas lay eggs.

Reptiles that don't lay eggs produces eggs inside their bodies that either have very thing shells or no shell at all. In the case of the former the young hatch from eggs while still in their mother's body and emerge live.

Reptile eggs contain considerable amounts of yoke. Some reptiles species provide their young with additional nourishment by producing eggs that attach to the uterus. The uterus and the embryo generate interlocking blood vessels that allow nutrients to be passed from the mother to her young.

Most reptiles bury their eggs or conceal them somehow and then abandon them. Some snakes actively guard them and fight off predators.

Many reptiles have no sex chromosomes. Instead gender is determined by temperature. In crocodiles for example males are hot: eggs incubated in sand above a certain “pivotal temperature” almost always hatch males. This could spell trouble if global warming takes hold and female crocodiles — and reptiles — become scarce.

Sea Turtle Shells

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Turtle shells consist of two parts: 1) the carapace, the upper, arched part; and 2) the plastron, the flat lower part. The carapace is attached to the backbone and ribs. The palstron is fused to the breastbone. In hard shelled turtles the bone is covered by a shield made of a horn-like material. Soft shelled turtles have a covering of tough skin over the bony shell. The leatherback turtle differs from all other turtles in that ribs and vertebrae are fused to the outer shell. The covering consisted of hundred of bony plates imbedded in the skin.

The carapace consists of two layers: an inner core of bony plates that are fused together, and an outer layers of shields made of hornlike keratin, called scutes. The shape and patterns of the scutes is a useful clue in identifying different species. A turtle's shell grows along with the animal and, unlike the skin of lizards and snakes, is not periodically shed.

Sea turtles are unable to retreat completely into their shells. They can feel objects moving across their shells. Some enjoy having their shells scratched.

Feeding Sea Turtles

Turtles don't have teeth. They chew and grasp things in their beak-like mouths with horny jaws that contain sharp, almost knifelike cutting edges. Some turtles are completely vegetarian. Others are completely carnivorous. Many are omnivorous, eating whatever they can find.

Sea turtles eat pelagic crustaceans, jellyfish, algae and insects blown from the shore. Jellyfish is a favorite of some species. Loggerhead turtles like to feed on Portuguese man-of-war. Turtles in Australia like to feed on deadly box jellyfish. Sometimes the turtles become so intoxicated with poison their eyes swell shut. Like humans, turtles eyes can water. When they being butchered it looks as if the are crying.

Sea Turtle Reproduction

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laying the eggs
Most male sea turtles spend their lives in the open sea, approaching the shore only during the mating season. Females stay closer to shore and climb on to the beach several times every two or three years to nest.

Sea turtles produce reptilian eggs that can only develop and hatch in the air. The developing embryos need gaseous oxygen. Without it they will suffocate and die. Every year after mating in the sea, females seek dry land to lay the eggs. Some turtle species have slow rates of reproduction. They can live to be 100 but don’t reach sexual maturity for 20 to 30 years and then lay eggs only once every two to four years.

Turtles have few opportunities to find mates in the open ocean and generally mate near sandy beaches or around reefs. During mating the male sea turtle clasps on to the back of a female's shell with his flippers and stays there sometimes for hours. Turtles mate year round. Sometimes two males will pile on a single female.

Turtle eggs have tough leathery shells. Females lay several dozen to several hundred eggs in a nest which they dig out with their hind legs. The buried eggs hatch in less than two months. Sand temperature play a part in sex determination. More females are born when it is warm and more males are born when it is cool.

Sea Turtle Nesting Sites and Migration

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covering the eggs
Sea turtles return to the same nesting sites en masse after drifting in the open sea. Many sea turtles migrate thousands of miles between feeding and nesting sites. Sometimes they travel on migration corridors. Some sea turtles circumnavigate the Pacific Ocean, paddling from Japan and Borneo to Mexico and Baja California.

No one knows how they navigate their way to these nesting sights or how they know when it is time to go. Scientist are trying lean more about their migration routes and how they navigate. Some theorize they have an internal compass that picks up magnetic signals from the earth. Traces of magnetic substances have been found in their brains.

Female turtles sometimes make several nests, each with 80 to 100 eggs. It takes about two hours for a female to dig her nest, deposit the eggs, and cover them up in the sand. Like other reptilian females she has no interest in her eggs and offspring after the eggs are laid. When the job is finished, she strains to drag herself back into the sea.

Artificial lights can confuse nesting turtles who use reflections on the ocean surface to orient themselves when they are on land. Noise doesn't bother them so much. They have difficulty hearing sound in the air. It was long believed that newly hatched turtles crawled toward the sun, but recent research seems to show may actually trying to get away from the shadows of the dunes.

Sea Turtle Hatchlings and Sand Temperatures

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All sea turtle eggs can develop into males or females hatchlings, with gender determined by the temperature of the sand in which the eggs are buried to incubate, with the pivotal temperature for hawksbill turtles, for example, being 84.6 degrees F. There are some concerns that global warming could cause mas extinction of sea turtles by causing sand temperatures to rise so much that only females would be born.

In recent year, research by Stephanie Jill Karmel of the University of Toronto has found that in places where there is a lot of human development and global warming is on the rise more females are being born as result of hotter sand associated with the development. Crocodiles also produce young whose sex is determined by the temperature of the eggs and some species are having the same problem.

A young sea turtle has less than a one in a thousand chance of living until maturity. Turtles eggs are eaten by fly larvae, fungi, crabs, feral dogs, racoons, and birds. When the hatchling emerge from their shells they are snatched up by birds that line the beach huge numbers, waiting to feast on them, and crabs that pull the hatchlings into their holes and eat only the tender flesh — the eyes, the necks and soft underbellies. Those the reach the open seas fall prey to sharks, groupers and fishnets.

Endangered Sea Turtles, Fishing, Egg Harvesting and Pollution

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heading back to the sea
In 1974, a 52-year-old woman on board a ship that caught fire and sunk 600 miles south of Manila, survived in the water for 48 hours, she said, with the help of a sea turtle "with a head as big as that of a dog." The woman said, the "turtle bit me gently every time I felt drowsy. maybe it wanted to prevent me from submerging my head in the water and drowning." When a ship finally showed up one rescuer mistook the turtle for an oil drum. "Someone threw her a life ring," he said. "The moment she transferred her hold to the ring, the drum sank. We did not realize it was a giant turtle until we started hauling the woman, for the turtle was beneath her apparently propping her up. It even circled twice before disappearing into the depths of the sea, as if to reassure itself that its former rider was in good hands." [Source: People Almanac II]

In return for such acts of altruism sea turtles have been killed for their meat, shells and leather. They are trapped in fishing net and coastal pollution poisons their coastal habitat. Their eggs are collected for food. Nesting sites have been lost to development and harvesting of eggs. According to one study which compared records of traders and pirates from historical times with modern research, more than 20 percent of the sea turtle nesting sites in the Caribbean have been lost completely and half the remaining ones have very small populations of turtles.

In many places especially in Latin America men eat turtle eggs as aphrodisiacs. In some places in Mexico they are sold on the streets for one dollar and eaten raw with lime and a pinch of salt. At one time turtles that nested on the Pacific, particularly in the southern Mexican state of Guerrero, were killed and the eggs were harvested from their corpses and the bodies were sold for meat.

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Sea turtle deaths used to be determined by tallying up turtle products such as boxes of meat, carved hair pins and leather goods. It is estimate that Mexico alone used to slaughter 75,000 olive ridleys annually until the killing was stopped by a presidential decree.

It was once thought that the greatest threat to the survival of sea turtles was overharvesting of their eggs. But now many blame pollution and fishing. Many sea turtles die by ingesting plastic bags which they mistake for jellyfish. They are also sucked up by dredges and affected by oil spills, pollution and algae blooms. Says one biologist, "Losing an adult sea turtle is like breaking thousands of eggs on the beach."

Commercial fishing is believed to be the No.1 cause of man-related sea turtle deaths. Thousands of sea turtles drown after getting caught in fisherman's nets. Environmental groups claim that nets on shrimp boats alone claim as many as 150,000 sea turtles a year.

See Fishing, Shrimp Fishing.

Studying and Helping Sea Turtles

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researchers collect eggs
To track the turtles satellite transmitters are attached to their shells. "Pop-up tags" continually measure the turtle’s position, depth, speed and direction. The data is stored digitally. After six months a minicomputer cause the release on electric signal that burns a magnesium wire, releasing the tag to the surface, where it releases a GPS locator signal. Satellites then find it and upload the data. One tagged female swam for 2,728 miles until its signal faded out. But even with these devises, a U.S. Fish and Wildlife scientist admitted "I don't know any branch of science where we have applied so much effort and learned so little."

Sea turtles that have lost their flippers for one reason or another have been outfitted with prosthesis in efforts to get them back in the water. A green turtle named Alison, for example, was found off South Padre Island in Texas with only flipper and was unable to swim except of going around and around in circles. She was given a neoprene suit that fit over her shell and a carbon-fiber dorsal fin that allows to glide around with other turtles. It is believed that Alison lost her other three flippers in a shark attack.

Alison was helped by a group called Sea Turtle Inc., a Texas nonprofit group that rehabilitates injured sea turtles. In most cases turtles with three flippers can be returned to the wild. Two flipper turtles are usually adopted by zoos but one flipper turtle are often euthanized because they have difficulty just reaching the surface for air.

The Sea Turtle Association of Japan, a nonprofit organization in Japan that helps sea turtles, developed a pair or artificial front flippers for a loggerhead sea turtle named Yu-cha that lost her two front flippers in a shark attack. The team working on her, through trial and error, developed several pairs of prosthesis. Yu-chan was discovered by fishermen. The hope is to release her back into the wild.

Sea Turtle Conservation, Eggs and Fishing

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baby leatherback
Shrimp boats in the United States and countries that export shrimp to the United States are now required by law to use nets outfit with trapdoor-like attachment called a Turtle Excluder Device (TED) that allows the turtles to escape. The TED is a panel of mesh webbing or metal grids at the end of the funnel-like shrimp nets that keeps turtles and large fish like sharks from entering and directs them to an escape hatch. Fishermen claim that devices cause them lose shrimp and money. In some places, fishing boats have been prohibiting from coming within two miles of nesting and feeding sites.

Newly-developed round fish hooks baited with mackerel can reduce the rate of unintentionally catching sea turtles with long lines using traditional J-style hooks baited with squid by 65 percent to 90 percent. Fishermen are also beginning to attach timers to their trawling nets. The vast majority of sea turtles survive entanglements in nets as long as they are pulled from the water within 50 minutes. Relatively low tech “tow-time loggers” measure how long nets have been underwaters and record the data to let government officials know it the nets have been pulled up with in the 50 minute limit.

Around sea turtle nesting sites local people have been educated about the problems facing turtles. In many places people have responded by halting the practice of eating turtle eggs and participating in beach patrols to catch poachers. Sometimes the eggs are collected and placed in a safe place to hatch.

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loggerhead hatchings
In an effort to debunk the notion that turtle eggs are aphrodisiacs an advertising campaign was launched in Mexico with a sexy Argentine actress who declared eating turtle eggs was not sexy. While the actress poses in a swimsuits the words “May man doesn’t need turtle eggs” appears “because he knows they don’t make him more potent.”

Great strides have been made bringing sea turtles back to large nesting sites and protecting smaller sites. Conservationists say the efforts to protect small sites is kind of hedge: if one of the large sites is devastated by a storm them then smaller ones can still be productive, they say. Olive Ridley turtles have made a comeback to nesting grounds in the state of Oaxaca in part because the nesting sites are watched over by armed federal agents.

Image Source: National Oceanic and Atmospheric Administration (NOAA); Wikimedia Commons

Text Sources: Mostly National Geographic articles. Also the New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated March 2011


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