Sea turtle

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Sea Turtles
Hawaiian Green Sea Turtle
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Order: Testudines Suborder: Cryptodira Superfamily: Chelonioidea Bauer, 1893
Genera
Family Cheloniidae (Oppel, 1811) Caretta Chelonia Eretmochelys Lepidochelys Natator Family Dermochelyidae Dermochelys Family Protostegidae (extinct) Family Toxochelyidae (extinct) Family Thalassemyidae (extinct)

Sea turtles (Chelonioidea) are turtles found in all the world's oceans except the Arctic Ocean, and some species travel between oceans. The Flatback turtle is found solely on the northern coast of Australia. The Leatherback Sea Turtle is the largest, measuring six or seven feet (2 m) in length at maturity, and three to five feet (1 to 1.5 m) in width, weighing up to 1300 pounds (600 kg). Most other species are smaller, being two to four feet in length (0.5 to 1 m) and proportionally less wide. There are seven types of sea turtles: Kemp's Ridley, Flatback, Green, Olive Ridley, Loggerhead, Hawksbill and the Leatherback. All but the Leatherback are in the family Chelonioidea; the Leatherback belongs to the family Dermochelyidae and is its only member.

Different species are distinguished by varying anatomical aspects: for instance, the prefrontal scales on the head, the number of and shape of scutes on the carapace, and the type of inframarginal scutes on the plastron. The Leatherback is the only sea turtle that does not have a hard shell, instead carrying a mosaic of bony plates beneath its leathery skin.

Contents 1 Ecology and Life History of Sea Turtles 1.1 Life History 2 Importance to Humans 3 Threats to Sea Turtles 4 Sea turtles and fragile ecosystems 5 Taxonomy 6 References 7 Further reading 8 External links

[edit] Ecology and Life History of Sea Turtles

[edit] Life History

Sea turtles have an extraordinary sense of time and location. They are highly sensitive to the Earth's magnetic field and use it to navigate. They can live up to 189 years. The fact that most species return to nest at the locations where they were born seems to indicate an imprint of that location's magnetic features. The Ridley turtles are especially peculiar because instead of nesting individually like the other species, they come ashore in one mass arrival known as an "arribada" (arrival). With the Kemp's Ridley this occurs during the day and on only one beach in the entire world. Their numbers used to range in the thousands but due to the effects of extensive egg poaching and hunting in previous years the numbers are now in the hundreds.

After about 30 years of maturing, adult female sea turtles return to the land to nest at night, usually on the same beach from which they hatched. This can take place every two to four years in maturity. They make from four to seven nests per nesting season. They dig a hole with their hind flippers and lay from 70 to 190 eggs in it (depending on the species) before covering it up and returning to the ocean. Some of the eggs are unfertilized 'dummy eggs' and the rest contain young turtles. Incubation takes about 2 months. When the eggs hatch, these baby turtles dig their way out and seek the ocean. Only a very small proportion of them (usually 1%) will be successful, as many predators wait to eat the steady stream of new hatched turtles (since many sea turtles lay eggs en masse, the eggs also hatch en masse).

The hatchlings then proceed into the open ocean, borne on oceanic currents that they often have no control over. While in the open ocean, it used to be the case that what happened to sea turtle young during this stage in their lives was unknown. However in 1987, it was discovered that the young of Chelonia and Caretta spent a great deal of their pelagic lives in floating sargassum beds - thick mats of unanchored seaweed floating in the middle of the ocean. Within these beds, they found ample shelter and food. In the absence of sargassum beds, turtle young feed in the vicinity of upwelling "fronts"^[1]

[edit] Importance to Humans

Marine turtles are caught worldwide, despite it being illegal to hunt most of the species in many countries.^[2][3]

A great deal of intentional marine turtle harvests worldwide is for the food industry. In many parts of the world, the flesh of sea turtles are considered fine dining. Texts dating back to the fifth century B.C. describes sea turtles as exotic delicacies in ancient China.^[4]

To a much lesser extent, specific species of marine turtles are targeted not for their flesh, but for their shells. Tortoiseshell, a traditional decorative ornamental material used in Japan and China, is derived from the carapace scutes of the hawksbill turtle.^[5][6] The use of marine turtle shells for decorative purposes is by no means limited to the orient. Since ancient times, the shells of sea turtles (primarily the hawksbill) have been used by the ancient Greeks and ancient Romans. Various articles and ornaments used by the elite of these societies, such as combs and brushes, were from processed turtle scutes.^[7]

[edit] Threats to Sea Turtles

A sea turtle's senses are very sharp. However, all species of sea turtles are threatened or endangered. The Leatherback, Kemp's ridley, and Hawksbill turtles are listed as critically endangered. The Olive ridley, and Green turtles are considered endangered, and the loggerhead is a threatened species^[8]. The Flat back is considered data deficient due to lack of research.

Sea turtles used to be hunted on a large scale in the whaling days for their meat, fat and shells.^{[citation needed]} Coastal peoples have also been known to gather turtle eggs for consumption.^{[citation needed]} One of their most significant threats now comes from bycatch due to various fishing methods. Long-line fishing has been blamed as one of the causes of accidental sea turtle deaths.^[9], and the black market demand for tortoiseshell ^[10] .

Nets used in shrimp trawling and fishing have been known to cause the accidental deaths of sea turtles. The turtles, as air-breathing reptiles, must surface to breathe. Caught in a fisherman's net, they are unable to go to the surface to breathe and suffocate to death in the net. In early 2007, almost a thousand sea turtles were killed inadvertently in the Bay of Bengal over the course of a few months as a result of becoming trapped in fishing nets.^[11]

However some relatively inexpensive changes to fishing techniques, such as slightly larger hooks and traps from which sea turtles can escape, can dramatically cut the mortality rate.^{[citation needed]} marine debris, especially from abandoned fishing nets in which they can become entangled.

Beach development is another area which poses threats to sea turtles. Since sea turtles return to the same beach locations to nest, if these areas are developed they may be left with nowhere to nest, or their nesting locations may be threatened by human activity. Therefore, there has been a movement to protect these areas. In some areas, such as the east coast of Florida, after the adult turtles lay their eggs, they are dug up and relocated to special fenced nurseries where they can be protected from beach traffic. This is not the best thing to do, as many turtle species return to the beach on which they were born. Special lighting ordinances may also be enforced to prevent lights from shining on the beach and confusing young hatchlings from thinking it is the moon or sun and crawling toward it, usually crossing a road.

Another major threat to sea turtles is the black market trade in eggs and meat. This is a pervasive problem throughout the world, but especially a concern in the province of Batangas in the Philippines, India, Indonesia and throughout the coastal nations of Latin America. Estimates are as high as 35,000 turtles killed a year in Mexico and the same number in Nicaragua. Conservationists in Mexico and the United States have launched "Don't Eat Sea Turtle" campaigns in order to reduce the urban black market trade in sea turtle products. These campaigns have involved figures such as Pope John Paul II, Dorismar, Los Tigres del Norte and Mana.

Injured sea turtles are sometimes able to be rescued and rehabilitated by professional organizations such as the Marine Mammal Center in Northern California.^[12]

[edit] Sea turtles and fragile ecosystems

Sea turtles play key roles in two ecosystems that are critical to them as well as to humans—the oceans and beaches/dunes. If sea turtles were to become extinct, the negative impact on beaches and the oceans would potentially be significant.

In the oceans, for example, sea turtles, especially green sea turtles, are one of the very few creatures (manatees are another) that eat a type of vegetation called sea grass that grows on the sea floor. Sea grass must be kept short to remain healthy, and beds of healthy sea grass are essential breeding and development areas for many species of fish and other marine life. A decline or loss of sea grass beds would mean a loss of the marine species that directly depend on the beds, which would trigger a chain reaction and negatively impact marine and human life. When one part of an ecosystem is destroyed, the other parts will follow.

Beaches and dunes are a fragile ecosystem that does not get many nutrients to support its vegetation, which is needed to help prevent erosion. Sea turtles contribute nutrients to dune vegetation from their eggs. Every year, sea turtles lay countless numbers of eggs in beaches during nesting season. Along one twenty-mile stretch of beach in Florida alone, for example, more than 150,000 pounds of eggs are laid each year. Nutrients from hatched eggs as well as from eggs that never hatch and from hatchlings that fail to make it into the ocean are all sources of nutrients for dune vegetation. A decline in the number of sea turtles means fewer eggs laid, less nutrients for the sand dunes and its vegetation, and a higher risk for beach erosion.

The plight of sea turtles has been recognized around the world, and many organizations and governments are working to preserve these ancient creatures. Volunteer opportunities to save the turtles ^[13] are available in North America and around the world.

[edit] Taxonomy

Seven distinct species of sea turtles grace our oceans today; they constitute a single radiation that was distinct from all other turtles at least 110 million years ago. During that radiation, sea turtles split into two main subgroups, which still exist today: the unique family Dermochelyidae, which consists of a single species, the leatherback; and the six species of hard-shelled sea turtle, in the family Cheloniidae. From SWOT Report, vol. 1.

• Family Cheloniidae
  • Chelonia mydas
  • Eretmochelys imbricata
  • Natator depressus
  • Caretta caretta
  • Lepidochelys kempii
  • Lepidochelys olivacea
• Family Dermochelyidae
  • Dermochelys coriacea

[edit] References

[edit] Further reading

Spotila, James R. (2004). "Sea Turtles: A Complete Guide to Their Biology, Behavior, and Conservation." Baltimore: Johns Hopkins University Press. ISBN 0-8018-8007-6.

[edit] External links

• SWOT - The State of the World's Sea Turtles - The most up-to-date information on global sea turtle populations
• Oceana scientists are tracking turtles in the Mediterranean and the Atlantic to find out more about their habits in the deep sea
• Conserving Turtles on a Global Scale