Sea turtle
| Sea Turtles | |
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| Hawaiian Green Sea Turtle | |
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| Superfamily: | Chelonioidea Bauer, 1893
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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 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.
Ecology and life history
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. The length of incubation and the gender of the hatchling depends on the temperature of the sand. Darker sands maintain higher temperatures, decreasing incubation time and increasing the frequency of female hatchlings. When the eggs hatch, these baby turtles dig their way out and seek the ocean. Only a very small proportion of them (usually .001%) 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 mydas and Caretta 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]
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] Historically, many coastal communities around the world have depended on sea turtles as a source of protein. Several turtles could be harvested at once and kept alive on their backs for months until needed.
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]
Threats
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 Flatback's conservation status is unclear due to a lack of research data.
Sea turtles used to be hunted on a large scale in the whaling days for their meat, fat and shells. Coastal peoples have also been known to gather turtle eggs for consumption. [9] 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,[10] and the black market demand for tortoiseshell for both decoration and supposed health benefits[11] .
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.[12]
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.[13] Turtle Excluder Devices (TEDS) have reduced sea turtle bycatch in shrimp nets by 97 percent. Another danger comes from 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
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. Sea turtles are often consumed during the Catholic holiday, Lent, even though they are reptiles, not fish. Conservation organizations have written letters to the Pope asking that he declare turtles meat.
Injured sea turtles are sometimes able to be rescued and rehabilitated by professional organizations such as the Mote Marine Laboratory in Sarasota, Florida and theMarine Mammal Center in Northern California.[14]
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 [15] are available in North America and around the world.
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
- Family Dermochelyidae
References
- ^ Carr, Archie (1987). "New Perspectives on the Pelagic Stage of Sea Turtle Development". Conservation Biology. 1 (2). Blackwell Publishing: 103–121. Retrieved 2007-02-15.
- ^ CITES (2006-06-14). "Appendices" (SHTML). Convention on International Trade in Endangered Species of Wild Flora and Fauna. Retrieved 2007-02-05.
{{cite web}}: Check date values in:|date=(help) - ^ UNEP-WCMC. "Eretmochelys imbricata". UNEP-WCMC Species Database: CITES-Listed Species. United Nations Environment Programme - World Conservation Monitoring Centre. A-301.003.003.001. Retrieved 2007-02-05.
- ^ Schafer, Edward H. (1962). "Eating Turtles in Ancient China". Journal of the American Oriental Society. 82 (1). American Oriental Society: 73–74. Retrieved 2007-02-16.
- ^ Heppel, Selina S. (June 1996). "Analysis of a Fisheries Model for Harvest of Hawksbill Sea Turtles (Eretmochelys imbricata)". Conservation Biology. 10 (3). Blackwell Publishing: 874–880. Retrieved 2007-02-16.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Strieker, Gary (2001-04-10). "Tortoiseshell ban threatens Japanese tradition". CNN.com/sci-tech. Cable News Network LP, LLLP. Retrieved 2007-03-02.
{{cite news}}: Check date values in:|date=(help) - ^ Casson, Lionel (1982). "Periplus Maris Erythraei: Notes on the Text". The Journal of Hellenic Studies. 102. The Society for the Promotion of Hellenic Studies: 204–206. Retrieved 2007-02-16.
- ^ US Fish and Wildlife Services. "Species Profile: Loggerhead sea turtle." 2007. February 22, 2007. [1]
- ^ Sam Settle, 1995. Marine Turtle Newsletter 68:8-13 [2]
- ^ Smith, Tim (2007-02-03). "Turtles and birdlife at risk from long-line fishing, claim campaigners". News. The Royal Gazette Ltd. Retrieved 2007-02-06.
{{cite news}}: Check date values in:|date=(help) - ^ "Atlantic Hawksbill Sea Turtle Fact Sheet". Endangered Species Unit. Retrieved 2007-02-07.
{{cite web}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ "Fishermen blamed for turtle deaths in Bay of Bengal". Yahoo! Science News. Yahoo! Inc. 2007-02-05. Retrieved 2007-02-06.
{{cite news}}: Check date values in:|date=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Irene Kinan . 2006. Marine Turtle Newsletter 113:13-14 [3]
- ^ The Marine Mammal Center . "Volunteer Opportunities." 2007. February 22, 2007.[4]
- ^ Mitchell, Deborah. Charity Guide. Save Sea Turtles and Sea Turtle Habitats. 2007. February 27, 2007.[5]
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.
Davidson, Osha Gray. (2001.) "Fire in the Turtle House: The Green Sea Turtle and the Fate of the Ocean." United States: United States of Public Affairs. ISBN 1-5864-8199-1.
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