Sea turtles (superfamily Chelonioidea) inhabit all of the world's oceans except the Arctic.
Sea turtles are caught worldwide, although it is illegal to hunt most species in many countries. A great deal of intentional 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. Many coastal communities around the world depend on sea turtles as a source of protein, often harvesting several turtles at once and keeping them alive on their backs until needed. Coastal peoples gather turtle eggs for consumption. Turtles are popular in Mexico as boot material and food. 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, comes from the carapace scutes of the hawksbill turtle. Ancient Greeks and ancient Romans processed turtle scutes (primarily from the hawksbill) for various articles and ornaments used by their elites, such as combs and brushes. The skin of the flippers are 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. Sea turtles enjoy immunity from the sting of the deadly box jellyfish and regularly eat them, helping keep tropical beaches safe for humans.
All species of sea turtles are listed as threatened or endangered. The leatherback, Kemp's Ridley, and hawksbill turtles are critically endangered. The Olive Ridley and green turtles are endangered, and the loggerhead is threatened. 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. Donnelly points to long-lining as a major cause of accidental sea turtle death. There is also black-market demand for tortoiseshell for both decoration and supposed health benefits. Turtles must surface to breathe. Caught in a fisherman's net, they are unable to surface and thus suffocate. 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. 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. 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 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 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. 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 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. 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 turtles meat. Climate change may also cause a threat to sea turtles. Since sand temperature at nesting beaches defines the sex of a 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. Fibropapillomatosis disease causes tumors in sea turtles. Injured sea turtles are sometimes rescued and rehabilitated by professional organizations, such as the Mote Marine Laboratory in Sarasota, Florida, the Marine Mammal Center in Northern California, the ClearWater Marine Aquarium in Clearwater, Florida, and the Sea Turtle Inc. organization in South Padre Island, Texas. One such 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. 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 turtles and olive ridleys were threatened. In Southeast Asia, the Philippines has had several initiatives dealing with the issue of 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 turtle eggs.
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. 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.
Taxonomy and evolution
Sea turtles, along with other turtles and tortoises, are part of the order Testudines. The seven living species of sea turtles are: flatback, green sea turtle, Hawksbill, Kemp's Ridley, Leatherback, Loggerhead and Olive Ridley. 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. Sea turtles constitute a single radiation that became distinct from all other turtles at least 110 million years ago.