The Most Amazing Reptile, The Green Sea Turtle Draft #2
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The Most Amazing Reptile, The Green Sea Turtle
As one of the oldest sea turtle species studied, the green sea turtle has given scientist much of what is known about sea turtles history. This species can be found throughout tropical and subtropical waters around the world. They can be found in shallow coastal waters, lagoons, bays, and in open seas. This green sea turtle nests on beaches of over 80 countries and feeds in coastal waters of over 140 nations. Usually solitary animals and even lethargic at times, they can be very social and speedy at certain times of the year. Once very abundant as Christopher Columbus reported on his voyage about them, today they are recognized as endangered and protected from exploitation in most countries worldwide (Wood etal, 1994).
Green sea turtles are ancient marine reptiles. They are one of the largest turtle species in the world. As is the case with all reptiles, the green sea turtle is a distant relative of the dinosaurs. The green sea turtle (Chelonia mydas) is a vertebrate described in the class Reptilia, a word derived from the Latin meaning to creep. Reptilis is a class of cold-blooded vertebrates. The green turtle is a large sea turtle belonging to the family Cheloniidae. It is the only species out of eight, or as some scientists today claim nine, in the genus Chelonia. The species extends throughout tropical and subtropical seas around the world, with two distinct populations in the Atlantic and Pacific Oceans. Each of these populations is genetically distinct, and each has their own set of nesting and feeding grounds within the populationÕs known range. The green sea turtle is known to be extremely picky about their feeding and mating sites. Entire generations will often alternately migrate between the same feeding and nesting areas traveling over many, many miles, The species has been harvested for centuries for food and jewelry but now it is threatened with extinction due to human cause (1992).
The green sea turtle has a dorsoventrally flattened body, a beaked head at the end of a short neck, and paddle-like arms well adapted for swimming. Although the Òaverage sizeÓ of an adult varies considerably, adult green turtles are known to grow to five feet long. The average weight of mature individuals is around four hundred and forty pounds. The largest ever recorded weighed eight hundred and seventy one pounds (Green Sea Turtle Fact Sheet).
There are a few characteristics anatomically that distinguish the green turtle from the other members of its family. The green sea turtleÕs snout is very short and its beak is unhooked. The horny sheath of the turtleÕs upper jaw possesses a slightly-denticulation edge while its lower jaw has stronger, serrated more defined denticulation. The dorsal surface of the turtleÕs head has a single pair of prefrontal scales. Compared to other sea turtles, the head is very small when compared to body size. The carapace or upper shell has five central scutes or horny, scale-like coverings, flanked by four pairs of lateral scutes. Underneath, the green sea turtle has four pairs of inframarginal scutes covering the area between the turtleÕs plastron or underside and its shell (1992).
As a reptile, the green sea turtle is a cold-blooded vertebrate that has scaly skin, breathe air with their lungs and have a three-chambered heart. The green sea turtles like all other species of turtles, have a two-piece shell. Their shells are large, oval or heart-shaped and streamlined to move smoothly through the water. The patterns on the upper part of the shell or carapace differ with the species. This makes it a very useful feature in identifying individual species. Unlike many terrestrial and freshwater turtles, sea turtles cannot hide their heads, tails and limbs in their shells for protection (Cornish, 2002). This turtle is known to have various color patterns that change over time as the turtle grows. Generally the upper portion of the oval-shaped shell, or carapace, is usually reddish-brown to gray, sometimes with darker radiating streaks or spots on each shield of the carapace, and the plastron, or underside or lower shell that encases the belly, is usually white or yellowish, thus their common name can be misleading. The speciesÕ common name is not from any particular green external coloration of the turtle. The green sea turtle named from the greenish color of the turtleÕs fat, which is only found in a layer between their inner organs and their shell. There are fours pairs of costal shields on each side of the central row of plates on the carapace (Hieth, 1980a).
Characters that distinguish the green sea turtle from other sea turtle species are a smooth carapace with four pairs of lateral (or costal) scutes and a single pair of elongated prefrontal scales between the eyes. ÒThe nuchal scute does not touch the first costal scute and the inframarginal scutes do not have pores.Ó (Pritchard etal, 1983). Each flipper has a single claw and the carapace is oval-shaped and depressed. ÒThe crawls of nesting green sea turtles are deeply cut, with symmetrical diagonal marks made by the front flippers. The limbs are dark-colored and lined with yellow, and are usually marked with a large dark brown spot in the center of each appendageÓ (2002).
Female and male green sea turtles look much alike. They differ mainly in the size of their tails and shape of their shells. FemalesÕ tails are short and do not extend beyond their rear flippers, while the malesÕ tails are considerably larger and extend well past the hind legs. The carapace of the females is also slightly domed. The front legs of sea turtles are wing-like and are used like flippers to move the turtles through the water. These huge powerful limbs make the turtle fast and great long distance swimmers. Their rear flippers are much smaller and spade shaped, they are used mainly for steering while swimming. Females use their rear legs to dig nests for their eggs. Because all four legs are adapted to water, movement on land is very slow awkward and very, very tiring. The green sea turtle also have large upper eyelids to protect their eyes from their predators. Their eyesight is excellent underwater, but on land they seem to be nearsighted when looking through air They lack external ears but do have ear canals covered by a flap of skin, and are quite sensitive to low-frequency sounds. These turtles absorb a great deal of salt from their diet when they drink seawater. ÒThey have salt glands in their eye sockets, which enables them to excrete excess salt. The salt concentration can be twice as much as in seawater. When female turtles nest they are said to cry: in reality, they are excreting salt via their eye glandsÓ (2006). While their sense of hearing is excellent their sense of smell is even better. This sense is so strong, that the females can smell the beaches from which they hatched. Females use this sense to bring them back to lay their own eggs on this very same beach. Some specialists also believe that their senses of smell and taste, along with their ability to detect slight variations in the EarthÕs magnetic field, are used to help them migrate between nesting and feeding grounds. They have an extraordinary sense of time and location (Cornish, 2002).
Very interestingly, the green sea turtles can be highly migratory, traveling as far as fifteen hundred miles between nesting and feeding grounds (1992). The green sea turtles usually are somewhat lethargic as they swim at a rate only slightly faster than most divers can easily swim. However, they are capable of sudden bursts of speed reaching twenty miles per hour. Green sea turtles are excellent divers and are often observed rising up from depths far deeper than average sport divers can safely swim. As the case with all cold-blooded animals, green sea turtles have very slow metabolic rates. This trait helps them routinely make dives that last forty-five minutes or longer, and when resting on the seafloor are known to remain submerged for several hours. This resting period should be distinguished from the long periods of hibernation. When hibernating, green sea turtles spend several months buried in mud on the seafloor. How they accomplish this feat without breathing continues to fascinate and perplex the scientific community (Hendrickson, 1958).
Green sea turtles are ancient marine reptiles from long ago. ÒMany millions of years ago reptiles were among the first large animals able to live on land away from water for extended periods. Specialists believe that turtles first appeared on earth during the Upper Triassic geological period, over 210 million years agoÓ (Biologists close in on mystery of sea turtles Ôlost yearsÕ; open ocean finding solves Ôembarrassing problemÕ). Their fossil recording the first steps of turtle evolution are scarce and often fragmentary. ÒThe nearly complete150 million year old discovery in South America sheds new information on the amazing evolution of this creatureÓ (Biologists close in on mystery of sea turtles Ôlost yearsÕ; open ocean finding solves Ôembarrassing problemÕ). Early Sea turtles were alive with the dinosaurs. Their population was plentiful during the Cretaceous period, about 130 million years ago. They have changed very little over the years except in size. However some adaptations have taken place. When these turtles first made their way seaward some of the adaptations that allowed them to survive on land worked against them in their new lives. First of all there large box-like body created drag, a characteristic that worked against efficient swimming. Over time they have developed smoother, more low profile bodies better adapted for life at sea. Secondly, they acquired a way of propelling themselves in water and their legs evolved into large paddle-like flippers. Larger pectoral muscles were needed to propel the flippers in dense seawater. These muscles required considerable space in the chest cavity, and in gaining this space sea turtles lost the ability to retract their head and limbs inside of their shells the way land-dwelling tortoises can. At one time, four families of sea turtles roamed the oceans of Earth, but today only two families remain: Òthe family Dermochelyidae that includes the leatherback turtle, and Cheloniidae, the group to which the green sea turtle and remaining species of sea turtles belongÓ (Forbes, 1992).
The fossil history of the chelonians before the triassic period is not all that clear, however there is little real evidence to tell us how, when and why one early reptilian group shortened their bodies and covered them with armour for protection.
In 1503, on his fourth and last voyage to the New World, Christopher Columbus reported that his ship came Òin sight of two very small and low islands, full of tortoises, as was all the sea about, insomuch that they looked like little rocks,Ó(Wood etal, 1994) thus these islands were called Tortugas, later changed to the Cayman Islands on which was once the site of a large green sea turtle ÒrookeryÓ (Wood etal, 1994). In the 16th and 17th centuries turtles played an important part in the exploration and exploitation of the region by Europeans, including pirates. Much of the early activity in the New World tropics was dependent on green turtles. ÒTurtle meat and eggs provided a seemingly unending supply of protein, and turtles could be kept alive on ships for long voyages by trussing the flippers together turning them on their backs and putting them in a shaded area of the deckÓ (Wood etal, 1994). Turtle oil was used for cooking, lamp fuel and as a lubricant. The Cayman Islands social and economic history is tied to the green sea turtle. The impact of these turtles on the development of the Islands is illustrated by the prominent role the turtle plays as symbol of the Islands, represented on the currency, on the national seal and on the flag. The turtle continues to play a prominent role in the economic future of these Islands because of the current land-based, commercial operation of the Cayman Turtle Farm on Grand Cayman. However, the present turtle population in the waters of these Islands is only a shadow of what was once considered the major nesting ground of the green sea turtle in the Caribbean (Wood etal, 1994).
Besides being used by the local residents and explorers of the Caribbean, the green sea turtle was shipped to Europe, mainly England, where it was considered a great delicacy for the meat and the lower shell that was used for soup. With the invention of steam travel, more and more turtles were being shipped alive. By 1878, 15,000 turtles a year were being shipped to England (Forbes, 1992).
Ò Early in the 1700Õs the green sea turtle population was becoming scarce in many areas. By the beginning of the 19th century the Cayman Island rookery was wiped out and shortly after that most others were goneÓ(Wood etal, 1994). In the last three decades, international regulations affecting all sea turtles have virtually eliminated trade of these turtles. Because of over fishing and habitat destruction, most populations of all sea turtle species are endangered or threatened (1992).
ÒLinnaeusin described the green sea turtle in 1758 as Testudo mydas with Ascension Island as the type locality. Schweigger first applied the binomial we use today, Chelonia mydas in 1812Ó(Pritchard etal, 1983). The taxonomic status of the green turtle is not clear. However, there is little genetic exchange among isolated breeding colonies, and, thus, these colonies may deserve sub-specific recognition. Although trinomials have been applied to various populations in the past, they are generally not in use today. Advances in DNA research are helping to answer questions by identifying genetically isolated populations (Allard, 1994).
The green sea turtles are found in both tropical and subtropical waters all over the world. ÒThey live in shallow coastal waters, lagoons, bays and estuaries as well as the waters of the open ocean in areas ranging from thirty degrees north to thirty degrees south of the equatorÓ (Green Sea Turtle Fact Sheet).
One very important aspect of green sea turtles is their ability to travel long distances and locate specific sites with remarkable precision. Green sea turtles are as loyal to nesting sites, as they are to preferred feeding grounds or sleeping rocks. Some of them may nest and graze in the same area and others will follow coastlines from feeding to nesting grounds and back. Some however, travel great distances over open water
The many beds of sea grasses found throughout the tropics serve as pastures for green sea turtles. Some populations of these turtles feed on algae. Adult green sea turtles are unique among sea turtles in being plant eaters. Because their diet is low in protein, green sea turtles grow slowly and sexual maturity is delayed. Dramatic variations in growth rates have been observed from one feeding area to another, and the differences have been attributed to food quality and temperature. Green sea turtles may breed for the first time when they are between twenty-five to fifty years old. This variable is also due to food quality and temperature (Forbes, 1992).
Because of the research work of Dr. Archie Carr in the mid 1950Õs, a great deal of information has been gained about the unique history of the green sea turtle concerning the Òlost years.Ó Life for this amazing sea creature begins two feet below the warm beach sand as the entire clutch of eggs begins to hatch after two months of incubation. About forty-eight hours after absorbing their yolk sack, the clutch starts the struggle to reach the top of the nest and free them of the sand. During this time events have occurred deep in the nest prior to hatching, that help to determine the sex of the sea turtle. The temperature of the sand determines this during incubation. Warm temperatures produce more females while cooler temperatures produce more males (Carr, 1952).
After leaving the sand the hatchlings scramble down the beach and into open water unaware of the many predators that await them. Those hatchlings which are successful in their journey to the open sea, will spend the next several years in what in referred to as the Òlost years,Ó however biologists have now found a major clue to a fifty year old mystery about Òwhat happens to green sea turtles after they crawl out of their sandy nests and vanish into the surf, only to reappear several years later close to the shore.Ó( Hendrickson, 1958). Three University of Florida sea turtle scientists say they found the clue by analyzing chemical elements ingrained in the turtlesÕ shells. ÒThus the first three to five Òlost yearsÓ of these hatchlings are spent in the open sea, feeding on jellyfish and other creatures as carnivores. Only after this period do they move closer to shore and switch to a vegetarian diet of sea grass, which is the period in their lives when they have long been observed and studiedÓ (Biologists close in on mystery of sea turtlesÕ lost yearsÕ; open ocean finding solves Ôembarrassing problemÕ).
This research is also very important because it may help in the conservation of the turtles, which, like all sea turtles, are classified as endangered. Although the life cycle of the green sea turtle has been the basis for it success, it is this very same life cycle that has proven detrimental for the green sea turtle in the presence of humans. Direct activities such as over harvesting and hunting and indirect ones such as habitat destruction and pollution are affecting turtle populations worldwide. Sea turtles are one of the most vulnerable of all marine vertebrates. Their survival is seriously threatened by factors such as loss of nesting sites, fishing and tourism. There is some evidence that young green sea turtles can confuse oil droplets for food and that some adults eat plastic bags, mistaking them for jellyfish. Poachers for eggs throughout the Pacific raid nests. Turtle skins are used for leather and their fat and oils for cosmetics. ÒIn the United States, eighty percent of all sea turtles nest in Florida where habitat degradation is the most serious problemÓ (1992). Many problems include beach lighting, which frightens nesting turtles and disorients hatchlings. Also, seawalls and bulkheads destroy nesting areas. The pumping of sand onto beaches to repair erosion buries nests and changes the quality of the sand. The use of beach cleaning machines crushes the nests (Cornish 2002).
The green sea turtle is the oceanÕs largest hard-shelled turtle. They are still the turtle heavily exploited even though they were among the first animal listed under the Endangered Species Act in 1973; they and their eggs continue to be hunted in much of their range today (Pritchard etal, 1998).
Because the green sea turtles feed in shallow coastal areas, they can be captured with nets, spears, and gaffs with relative ease. When the female comes onto the beach to lay her eggs, she and her eggs are easy prey. Those few countries that provide protection for sea turtles cannot stop the decline of the sea turtles, since sea turtles do not respect international boundaries during their migrations. These turtles may spend up to fifty years maturing in a country where they are afforded protection only to migrate to their breeding grounds in another country where they will be hunted (Forbes 1992).
The United States along with one hundred fifteen other countries are banning together to ban import or export of sea turtle products. The green sea turtle being placed on the United States endangered species list prevents the legal importing of turtle products into this country, but there is a large international illegal trade in turtle products These turtles also are still dying in shrimp nets and the accidental catch is about 40,000 turtles per year with an estimated mortality of forty-two percent (Green Sea Turtle Fact Sheet).
As far as the future of the green sea turtle goes, we are hopeful that someday these turtles will be protected from commercial takes in all countries. Until that day comes about, many, many thousands of green sea turtles around the world will lose their lives. Even though the green sea turtle has been on this planet for many millions of year, if we continue at the current rate of exploitation, it may not survive the next generation of poachers.
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