Sea turtle
Sea turtles
An olive ridley sea turtle
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Suborder: Cryptodira
Superfamily: Chelonioidea
Bauer, 1893
Genera

Sea turtles (superfamily Chelonioidea and Dermochelyidae) are marine reptiles that inhabit all of the world's oceans except the Arctic.

Contents

Distribution

The superfamily Chelonioidea has a world-wide distribution; sea turtles can be found in all oceans except for the polar regions.[citation needed] Some species travel between oceans. The flatback sea turtle is found solely on the northern coast of Australia.

Biology

Respiration

A Green sea turtle breaks the surface to breathe.

Sea turtles are almost always submerged in water, and, therefore, have developed an anaerobic system of respiration. Although all sea turtles breathe air, under dire circumstances they may divert to anaerobic respiration for long periods of time. When surfacing to breathe, a sea turtle can quickly refill its lungs with a single explosive exhalation and rapid inhalation. Their large lungs have adapted to permit rapid exchange of oxygen and to avoid trapping gases during deep dives. However, sea turtles must emerge while breeding, given the extra level of activity.

Life history

Hawksbill sea turtle swims at Black Hills, Honduras
A feeding green sea turtle, Chelonia mydas

According to SeaWorld Parks & Entertainment, a lifespan of 80 years is feasible for sea turtles.[1]

It takes decades for sea turtles to reach sexual maturity. After mating at sea, adult female sea turtles return to land to nest at night. Different species of sea turtles exhibit various levels of philopatry. In the extreme case, females return to the beach where they hatched. This can take place every two to four years in maturity. They make from one to eight nests per season.

The mature nesting female hauls herself onto the beach, nearly always at night, and finds suitable sand on which to create a nest. Using her hind flippers, she digs a circular hole 40 to 50 centimetres (16 to 20 in) deep. After the hole is dug, the female then starts filling the nest with a clutch of soft-shelled eggs one by one until she has deposited around 50 to 200 eggs, depending on the species. Some species have been reported to lay 250 eggs, such as the hawksbill. After laying, she re-fills the nest with sand, re-sculpting and smoothing the surface until it is relatively undetectable visually. The whole process takes thirty to sixty minutes. She then returns to the ocean, leaving the eggs untended.[2]

The hatchling's gender depends on the sand temperature. Lighter sands maintain higher temperatures, which decreases incubation time and results in more female hatchlings.

Incubation takes about two months. The eggs in one nest hatch together over a very short period of time. When ready, hatchlings tear their shells apart with their snout and dig through the sand. Again, this usually takes place at night, when predators such as seagulls cannot fly. Once they reach the surface, they instinctively head towards the sea. If, as happens on rare occasions, hatching takes place during daylight, only a very small proportion of each hatch (usually 0.01%) succeed, because local opportunist predators, such as the common seagull, gorge on the new sea turtles. Thus there is an obvious evolutionary drive to hatch at night, when survival rates on the beach are much higher.

The hatchlings then proceed into the ocean, where a variety of marine predators await them. In 1987, Carr discovered that the young of Chelonia mydas and Caretta caretta spent a great deal of their pelagic lives in floating sargassum beds, where there are thick mats of unanchored seaweed. Within these beds, they found ample shelter and food. In the absence of sargassum beds, sea turtle young feed in the vicinity of upwelling "fronts".[3] In 2007, Reich determined that green sea turtle hatchlings spend the first three to five years of their lives in pelagic waters. In the open ocean, pre-juveniles of this particular species were found to feed on zooplankton and smaller nekton before they are recruited into inshore seagrass meadows as obligate herbivores.[4][5]

Instead of nesting individually like the other species, Ridley sea turtles come ashore en masse, known as an "arribada" (arrival). With the Kemp's ridley sea turtles this occurs during the day.

Salt gland

Sea turtles possess a salt excretory gland at the corner of the eye, in the nostrils, or in the tongue, depending on the species; chelonian salt glands are found in the corner of the eyes in leatherback sea turtles. Due to the iso-osmotic makeup of jellyfish and the other gelatinous prey upon which sea turtles subsist, sea turtle diets are high in salt; chelonian salt gland excretions are almost entirely composed of sodium chloride 1500-1800 mosmoll-1 (Marshall and Cooper, 1988; Nicolson and Lutz, 1989; Reina and Cooper, 2000).

Importance to humans

Moche Sea Turtle. 200 A.D. Larco Museum Collection, Lima, Peru
"Manner in which Natives of the East Coast strike turtle". Near Cooktown, Australia. From Phillip Parker King's Survey. 1818.

Marine sea turtles are caught worldwide, although it is illegal to hunt most species in many countries.[6][7] A great deal of intentional marine sea turtle harvests worldwide are for food.

Many parts of the world have long considered sea turtles to be fine dining. Ancient Chinese texts dating to the fifth century B.C. describe sea turtles as exotic delicacies.[8] Many coastal communities around the world depend on sea turtles as a source of protein, often harvesting several sea turtles at once and keeping them alive on their backs until needed. Coastal peoples gather sea turtle eggs for consumption.[9]

Sea turtles are popular in Mexico as boot material and food.[10]

To a much lesser extent, specific species of marine sea turtles are targeted not for their flesh, but for their shells. Tortoiseshell, a traditional decorative ornamental material used in Japan and China, comes from the carapace scutes of the hawksbill sea turtle.[11][12] Ancient Greeks and ancient Romans processed sea turtle scutes (primarily from the hawksbill) for various articles and ornaments used by their elites, such as combs and brushes.[13] The skin of the flippers is prized for use as shoes and assorted leather goods.

The Moche people of ancient Peru worshipped the sea and its animals. They often depicted sea turtles in their art.[14]

Sea turtles enjoy immunity from the sting of the deadly box jellyfish and regularly eat them, helping keep tropical beaches safe for humans.

Sea turtles, especially green sea turtles, are one of the few animals that eat sea grass. Sea grass needs to be constantly cut short to help it grow across the sea floor. Sea turtles act as grazing animals that cut the grass short and help maintain the health of the sea grass beds. Sea grass beds provide breeding and developmental grounds for numerous species of fish, shellfish and crustaceans. Without sea grass beds, many marine species humans harvest would be lost, as would the lower levels of the food chain. The reactions could result in many more marine species eventually becoming endangered or extinct.[15]

Beaches and dune systems do not get many nutrients. Sea turtles use beaches and the lower dunes to nest and lay their eggs. Sea turtles lay around 100 eggs in a nest and make between 3 and 7 nests during the summer nesting season. Along a 20-mile stretch of beach on the east coast of Florida sea turtles lay over 150,000 lbs of eggs in the sand. Dune vegetation is able to grow and become stronger with the presence of nutrients from sea turtle eggs, unhatched nests, eggs and trapped hatchlings. As the dune vegetation grows stronger and healthier, the health of the entire beach/dune ecosystem becomes better. Stronger vegetation and root systems help to hold the sand in the dunes and help protect the beach from erosion.[15]

Beach towns, such as Tortuguero, Costa Rica, have transitioned from a tourism industry that made profits from selling sea turtle meat and shells to an ecotourism-based economy. Tortuguero is considered to be the founding location of sea turtle conservation. In the 1960s the cultural demand for sea turtle meat, shells, and eggs was quickly killing the once abundant sea turtle populations that nested on the beach. The Caribbean Conservation Corporation began working with villagers to promote ecotourism as a permanent substitute to sea turtle hunting. Sea turtle nesting grounds became sustainable. Since the creation of a sea turtle, ecotourism-based economy, Tortugero annually houses thousands of tourists who visit the protected 22-mile beach that hosts sea turtle walks and nesting grounds.[16][17]

Conservation

Legal notice posted by nest at Boca Raton, Florida

All species of sea turtles are listed as threatened or endangered. The leatherback, Kemp's Ridley, and hawksbill sea turtles are critically endangered.[18][19] The Olive Ridley and green sea turtles are endangered, and the loggerhead is threatened.[20] The flatback's conservation status is unclear due to lack of data.

One of the most significant threats now comes from bycatch due to imprecise fishing methods. Long-lining has been identified as a major cause of accidental sea turtle death.[21][22] There is also black-market demand for tortoiseshell for both decoration and supposed health benefits.[23]

Sea turtles must surface to breathe. Caught in a fisherman's net, they are unable to surface and thus drown. In early 2007, almost a thousand sea turtles were killed inadvertently in the Bay of Bengal over the course of a few months after netting.[24]

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.[25][26] 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 threatens sea turtles. Since many sea turtles return to the same beach each time to nest, development can disrupt the cycle. There has been a movement to protect these areas, in some cases by special police. In some areas, such as the east coast of Florida, conservationists dig up sea turtle eggs and relocate them to fenced nurseries to protect them from beach traffic.

Since hatchlings find their way to the ocean by crawling towards the brightest horizon, they can become disoriented on developed stretches of coastline. Lighting restrictions can prevent lights from shining on the beach and confusing hatchlings. Sea turtle-safe lighting uses red or amber LED light, invisible to sea turtles, in place of white light.

Another major threat to sea turtles is black-market trade in eggs and meat. This is a problem throughout the world, but especially a concern in the Philippines, India, Indonesia and the coastal nations of Latin America. Estimates reach as high as 35,000 sea 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 this trade in sea turtle products. These campaigns have involved figures such as Dorismar, Los Tigres del Norte and Maná. Sea turtles are often consumed during the Catholic season of Lent, even though they are reptiles, not fish. Consequently, conservation organizations have written letters to the Pope asking that he declare sea turtles meat.[citation needed]

A loggerhead sea turtle escapes a circular fisherman's net via a TED.
Loggerhead sea turtle exits from fishing net through a turtle excluder device (TED)

Climate change may also cause a threat to sea turtles. Since sand temperature at nesting beaches defines the sex of a sea turtle while developing in the egg, there is concern that rising temperatures may produce too many females. However, more research is needed to understand how climate change might affect sea turtle gender distribution and what other possible threats it may pose.[27]

Fibropapillomatosis disease causes tumors in sea turtles.

Injured sea turtles are sometimes rescued and rehabilitated by professional organizations, such as The Loggerhead Marinelife Center in Juno Beach, FL, The Turtle Hospital in Marathon, Florida, the Mote Marine Laboratory in Sarasota, Florida, the Marine Mammal Center in Northern California, the Clearwater Marine Aquarium in Clearwater, Florida,[28] and the Sea Turtle Inc. organization in South Padre Island, Texas.[29][30] One such sea turtle, named Nickel for the coin that was found lodged in her throat, lives at the Shedd Aquarium in Chicago.

In the Caribbean, researchers are having some success in assisting a comeback.[31] In September 2007, Corpus Christi, Texas, wildlife officials found 128 Kemp's ridley sea turtle nests on Texas beaches, a record number, including 81 on North Padre Island (Padre Island National Seashore) and four on Mustang Island. Wildlife officials released 10,594 Kemp's ridleys hatchlings along the Texas coast this year.

Also in 2007, the U.S. Fish and Wildlife Service and the National Marine Fisheries Service issued a determination that the leatherback, the hawksbill and the Kemp's Ridley populations were endangered while that of green sea turtles and olive ridleys were threatened.[32]

In Southeast Asia, the Philippines has had several initiatives dealing with the issue of sea turtle conservation. In 2007, the province of Batangas in the Philippines declared the catching and eating of Pawikans illegal. However, the law seems to have had little effect as Pawikan eggs are still in demand in Batangan markets. In September 2007, several Chinese poachers were apprehended off the Turtle Islands in the country's southernmost province of Tawi-Tawi. The poachers had collected more than a hundred sea turtles, along with 10,000 sea turtle eggs.[33]

Evaluating the progress of conservation programs is difficult, because many sea turtle populations have not been assessed adequately.[34] Most information on sea turtle populations comes from counting nests on beaches, but this doesn’t provide an accurate picture of the whole sea turtle population.[35] A 2010 United States National Research Council report concluded that more detailed information on sea turtles’ life cycles, such as birth rates and mortality, is needed.[36]

Sea turtles are very vulnerable to oil pollution, both because of their tendency to linger on the water's surface, and because oil can effect them at every stage of their life cycle.[37] Oil can poison the sea turtles upon entering their digestive system.

Fragile ecosystems

Sea turtles on a beach in Hawaii

Sea turtles play key roles in two ecosystem types that are critical to them as well as to humans—oceans and beaches/dunes. In the oceans, for example, sea turtles, especially green sea turtles, are one of very few creatures (manatees are another) that eat the 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 damage these populations, triggering a chain reaction and negatively impacting marine and human life.

Beaches and dunes form a fragile ecosystem that depends on vegetation to protect against erosion. Eggs, hatched or unhatched, and hatchlings that fail to make it into the ocean are nutrient sources for dune vegetation[citation needed]. Every year, sea turtles lay countless eggs on beaches. Along one twenty-mile (32 km) stretch of beach in Florida alone, for example, more than 150,000 pounds of eggs are laid each year.

Threats to sea turtles

Of the seven species of sea turtles,[38] all are listed on the IUCN Red List of Endangered Species as either "endangered" or "critically endangered".[39] Although sea turtles usually lay around one hundred eggs at a time, on average only one of the eggs from the nest will survive to adulthood.[40] While many of the things that endanger these hatchlings are natural, such as predators including sharks, raccoons, foxes, and seagulls,[41] many new threats to the sea turtle species have recently arrived and increased with the ever-growing presence of humans.[42]

Taxonomy and evolution

Immature Hawaiian Green sea turtle in shallow waters
Paleomedusa testa fossil at the Museum für Naturkunde, Berlin

Sea turtles, along with other turtles and tortoises, are part of the order Testudines.

The seven living species of sea turtles are: flatback sea turtle, green sea turtle, hawksbill sea turtle, Kemp's ridley sea turtle, leatherback sea turtle, loggerhead sea turtle and olive ridley sea turtle.[43] All species except the leatherback are in the family Cheloniidae. The leatherback belongs to the family Dermochelyidae and is its only member.

The species are primarily distinguished by their anatomy: 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, it bears a mosaic of bony plates beneath its leathery skin. It is the largest sea turtle, measuring 6 to 7 feet (1.8 to 2.1 m) in length at maturity, and 3 to 5 feet (0.91 to 1.5 m) in width, weighing up to 1,300 pounds (590 kg). Other species are smaller, being mostly 2 to 4 feet (0.61 to 1.2 m) and proportionally narrower.[44][not in citation given]

Sea turtles constitute a single radiation that became distinct from all other turtles at least 110 million years ago.

From SWOT Report, vol. 1:

Cladogram

Below is a cladogram showing the phylogenetic relationships of living and extinct sea turtles in the family Cheloniidae based on Lynch and Parham (2003)[45] and Parham and Pyenson (2010).[46]

Phylogenetic relations of living and extinct Cheloniidae species[45]
Cheloniidae sensu lato 

Toxochelys




Mexichelys




†Lophochleyinae




Euclastes




Argillochelys



Eochelone





Erquelinnesla



Pacifichelys





Puppigerus


 Cheloniidae sensu stricto 

Syllomus




Procolpochelys




Chelonia mydas



Natator depressus





Eretmochelys imbricata


 Carettini 
 Lepidochelys 

Lepidochelys kempii



Lepidochelys olivacea




Caretta caretta













See also

Florida Box Turtle Digon3.jpg Turtles portal

Additional reading

References

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  2. ^ Audubon, Maria R. (1897/1986). Audubon and His Journals: Dover Publications Reprint. New York: Scribner's Sons. pp. 373–375. ISBN 978-0486251448. 
  3. ^ Carr, Archie (August 1987). "New Perspectives on the Pelagic Stage of Sea Turtle Development". Conservation Biology (Blackwell Publishing) 1 (2): 103–121. doi:10.1111/j.1523-1739.1987.tb00020.x. JSTOR 2385827. 
  4. ^ Reich, Kimberly J.; Karen A. Bjorndal & Alan B. Bolten (18 September 2007). "The 'lost years' of green turtles: using stable isotopes to study cryptic lifestages". Biology Letters 6 (in press): 712–4. doi:10.1098/rsbl.2007.0394. PMC 2391226. PMID 17878144. http://www.journals.royalsoc.ac.uk/content/k1l8072271716750/. Retrieved 20 September 2007. 
  5. ^ Brynner, Jeanna (19 September 2007). "Sea Turtles' Mystery Hideout Revealed". LiveScience (Imaginova Corp.). http://www.livescience.com/animals/070919_sea_turtle.html. Retrieved 20 September 2007. 
  6. ^ CITES (14 June 2006). "Appendices" (SHTML). Convention on International Trade in Endangered Species of Wild Flora and Fauna. http://www.cites.org/eng/app/appendices.shtml. Retrieved 5 February 2007. 
  7. ^ UNEP-WCMC. "Eretmochelys imbricata A-301.003.003.001". UNEP-WCMC Species Database: CITES-Listed Species. United Nations Environment Programme - World Conservation Monitoring Centre. http://sea.unep-wcmc.org/isdb/CITES/Taxonomy/tax-species-result.cfm?displaylanguage=eng&Genus=Eretmochelys&Species=imbricata&source=animals&Country=&tabname=all. Retrieved 5 February 2007. 
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External links


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Look at other dictionaries:

  • Sea turtle — Sea tur tle (Zo[ o]l.) (a) Any one of several very large species of chelonians having the feet converted into paddles, as the green turtle, hawkbill, loggerhead, and leatherback. They inhabit all warm seas. (b) The sea pigeon, or guillemot. [1913 …   The Collaborative International Dictionary of English

  • sea turtle — sea turtles N COUNT A sea turtle is a large reptile which has a thick shell covering its body and which lives in the sea most of the time. [AM] (in BRIT, use turtle) …   English dictionary

  • sea turtle — any of several large turtles of the families Cheloniidae and Dermochelyidae, widely distributed in tropical and subtropical seas, having the limbs modified into paddlelike flippers: all sea turtles are either threatened or endangered through most …   Universalium

  • sea turtle — noun any of various large turtles with limbs modified into flippers; widely distributed in warm seas • Syn: ↑marine turtle • Hypernyms: ↑turtle • Hyponyms: ↑green turtle, ↑Chelonia mydas, ↑loggerhead …   Useful english dictionary

  • sea-turtle — noun A variant form of sea turtle …   Wiktionary

  • sea turtle — sea′ tur tle n. ram any of several large turtles of the families Cheloniidae and Dermochelyidae, widely distributed in tropical and subtropical seas, having the limbs modified into paddlelike flippers • Etymology: 1670–80 …   From formal English to slang

  • sea turtle — noun Date: 1612 any of two families (Cheloniidae and Dermochelyidae) of widely distributed marine turtles that have the feet modified into paddles and that include the green turtle, leatherback, hawksbill, loggerhead, and ridley …   New Collegiate Dictionary

  • sea turtle — noun Any turtle that inhabits oceans …   Wiktionary

  • sea turtle — heavily armored crawling animal that lives in salty water …   English contemporary dictionary

  • sea-turtle — …   Useful english dictionary

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