LEATHERBACK SEA TURTLE
Once a male leatherback sea turtle struggles from its egg and makes its way to the sea as a 4-inch (10 cm) hatchling, it may never again return to land during its 80-year lifetime.
Although they are air-breathing animals born on land, leatherbacks, like all sea turtles, spend their lives in the ocean. Females return to land only to lay their eggs.
The leatherback sea turtle is the largest sea turtle. It can grow up to 6.5 feet (2 m) long and weigh 1,400 pounds (636 kg). The leatherback gets its name from its shell, which is like a thick leathery skin, with the texture of hard rubber.
The leatherback sea turtle is a circumglobal species, meaning that it can range throughout almost all the oceans of the world. It nests on tropical beaches in the Atlantic, Indian, and Pacific Oceans.
Once abundant throughout the world’s oceans, all eight species of sea turtles are now threatened or endangered.
Leatherback sea turtle populations have plummeted in recent years. In the 1980s the worldwide population was estimated at nearly 100,000. Breeding populations are distinct, however, and many are highly endangered. On one important nesting beach in Mexico, there were 6,500 nests recorded in 1986, but only 50 by 1993.
Leatherback sea turtles are unique among sea turtles in that their primary food is jellyfish. They also will eat fish, mollusks, squid, sea urchins, and other marine creatures. Adult leatherbacks ply the seas alone, except on occasion gathering to feed in areas with large numbers of jellyfish.
Sea turtles swim with grace and speed and have been clocked at an amazing 22 miles per hour. They are also remarkable among reptiles in that they can survive in cold waters; they have been reported as far north as Norway and south off the coasts of Chile and New Zealand.
This range is possible because leatherback sea turtles can keep their body temperature warmer than the water surrounding them, due to a thick, oily, fat layer under their skin and their ability to shunt (turn off) bloodflow away from cold flippers. All other sea turtles are confined to the warmer regions of the world’s oceans.
Leatherback sea turtles require warm tropical beaches to incubate their eggs. After mating with a male just off shore, the female waits for nightfall to clamber up the beach, dig a shallow pit in the sand, and deposit her eggs. The female then buries the eggs with her hind flippers and compacts the sand with the weight of her body before crawling back to the sea.
Although a female may lay as many as 100 to 150 eggs at time, only a few will survive to grow to adulthood and breed. Life is perilous for a tiny hatchling sea turtle. They are a favorite food for natural predators such as raccoons, seabirds, sharks, and large fishes. If it can survive to adulthood, spending as long as 10 to 15 years at sea, a turtle will return to breed at the same beach where it hatched.
Causes of Endangerment
Sea turtle eggs are a prized food for humans and animals alike. They are easy prey, simply waiting to be dug up once the female turtle returns to the sea. Turtle eggs are used in traditional Asian medicines, and in most parts of the tropical world the eggs are an important part of local diets. Latin Americans covet sea turtle eggs as an aphrodisiac and energizing protein.
As a natural defense, sea turtles lay a large number of eggs. This defense is breaking down under the pressure of increased human harvesting and disturbance of nesting beaches. In some areas people harvest nearly 100 percent of eggs immediately after they are laid. Domestic dogs and pigs, which accompany human settlement, also are lethal predators of turtle eggs and hatchlings.
Humans have long hunted adult sea turtles for food and for their shells and other parts. In Indonesia, for example, shops are full of turtle souvenirs, turtle-skin bags, jewelry made from shells, and stuffed turtles, all of which are marketed to tourists. Sea turtles have suffered from the growing taste for turtle soup, considered a delicacy in Europe.
Leatherback sea turtles are killed to be rendered into oil for caulking boats in the Persian Gulf, for use in oil lamps in Papua New Guinea, and for medicinal use in the Caribbean. In the Solomon Islands, hunting sea turtles, including leatherbacks, is considered an important cultural event.
Japan historically has been the largest importer of sea turtle products in the world. Between 1970 and 1989, Japan imported 1.5 million pounds (680 metric tons) of shell, which represents about 700,000 dead turtles.
Sea turtles have used the same nesting beaches for thousands of years. The nesting beaches turtles prefer are often the same beaches most heavily used by people, and nesting turtles are easily disturbed by noise and bright lights. All over the world, hotels, restaurants, and homes have encroached on turtle nesting beaches.
Female turtles are frightened away and eggs are crushed by humans sunbathing, playing, and driving on the beaches. Upon hatching, the baby turtles often get confused by the lights of buildings near the beach; they are supposed to be drawn to the bright white light of the surf. When they get confused, they can go the wrong way and die.
Because sea turtles make lengthy migrations from hatching beaches to feeding grounds and back, they are exposed to a wide variety of threats. Pacific loggerhead sea turtles, for example, hatch on Japanese beaches and then swim 7,500 miles (12,000 km) to favored feeding grounds off Baja California.
Already declining due to heavy hunting of eggs and adults, large numbers of sea turtles are killed each year in fishing nets. Driftnets, huge floating nets as much as 30 miles (48 km) long, kill untold numbers of sea turtles, along with dolphins and seabirds (see Spotlight on Threatened Marine Life). Caught in a net and unable to surface for air, sea turtles can drown in 40 minutes.
Until recently an estimated 55,000 sea turtles died from shrimp trawling in United States waters each year. Shrimp trawl boats drag nets that scoop up shrimp as well as every other living thing in their paths. It is a wasteful fishing method, with unwanted animals making up as much as 80 percent of the weight of the total catch. That means 5 pounds of dead fish, clams, and other marine animals are thrown overboard for every pound of shrimp!
The burgeoning long-line fishing industry is now suspected to be the primary danger to sea turtle survival. Longliner ships set out fishing lines up to 75 miles (121 km) long, hung with thousands of hooks. Tens of thousands of sea turtles are snagged and drown on longlines yearly. Leatherback sea turtles in particular may be attracted to long-lines by the chemical light sticks attached to the lines, which may resemble the jellyfish that constitute their primary food.
Their preference for jellyfish makes leatherback sea turtles susceptible to another threat: floating plastic garbage in the oceans. Nearly 50 percent of leatherbacks recently studied had plastic bags or cellophane lodged in their stomachs or intestines. Dead sea turtles have been reported containing everything from pieces of plastic milk jugs to bits of balloons, items likely ingested when mistaken for jellyfish.
The United States and 115 other countries have banned the import or export of sea turtle products through CITES. However, the pressures on sea turtles are not abating and some illegal trade in turtle products continues. Although attempts are being made to control international trade, localized exploitation of turtles and eggs at the nesting beaches is still a problem.
Efforts to protect these species need to focus on the nesting beaches. Sea turtles are only nominally protected by law in most countries where nesting occurs. For example, the extremely endangered Malaysian leatherback sea turtles are still heavily exploited by local peoples. On one nesting beach, 1500 leatherbacks were counted in the 1950s, yet by the early 1990s fewer than 50 came ashore.
Another beach in Malaysia is the site of a creative “managed exploitation” effort aimed at saving the species while allowing some human use of turtle eggs. Adult sea turtles are now strictly protected, but egg collection by licensed collectors is allowed.
The government issues permits and then buys back a percentage of the collected eggs for captive incubation, hatching, and release of turtles to the wild. The permit fees paid by egg collectors contribute to the cost of running the hatchery. This combination of species conservation and local utilitization may be a model for other places. (See similar “sustainable use” projects described in case studies of the Queen Alexandra Birdwing Butterfly and the Dwarf Crocodile).
Hatcheries and headstarting are two programs aimed at increasing survival of sea turtles in the wild. Hatchery programs are intended primarily to protect eggs from predators. The programs typically consist of gathering eggs from the beach and reburying them in a fenced enclosure.
After the eggs hatch, the hatchlings are released onto the same beach from which the eggs were gathered. Headstarting projects go one step further. After collecting and hatching eggs from the wild, the sea turtles are reared in captivity for nine months to a year. Once the young turtles have reached a size more able to survive predation, they are released onto their natal beaches.
Steps are being taken to reduce the deaths of sea turtles in fishing nets. Since 1989, federal regulations in the United States require the use of Turtle Excluder Devices, or TEDs, on shrimp trawl nets. TEDs are grates that allow shrimp to pass into the net while turtles escape through a trap door.
The TEDs have been shown to be very effective in saving sea turtles. Critics claim, however, that some shrimp trawlers wire the TEDs closed and there is no means of effectively enforcing the law.
Migratory or free-ranging species such as sea turtles require international agreements for conservation to be successful. The use of high-seas driftnets was made illegal in 1993 under a moratorium resolution passed by the United Nations.
The leatherback sea turtle is not easily kept in captivity. Because it is adapted to life in the open sea, the leatherback has no “reverse gear” and will repeatedly swim into any obstacle in its path, including the walls of a holding tank. Other sea turtles have fared better in captivity and perhaps breeding programs can improve their chances for survival.
The most successful sea turtle breeding program is on Grand Cayman Island in the Caribbean. Turtles now breed in tanks and lay their eggs on artificial beaches, where the eggs are collected and incubated to ensure maximum survival of hatchlings. The farm sells turtle meat, oil, livers, skins for leather, and shell for ornaments.
Critics of turtle farming contend that rather than reducing poaching, it merely feeds demand for turtle products.
Due to a critical error made by the founders, it appears that this turtle farm and others like it will never be a able to contribute any turtles to the wild. The farm was first started with wild turtle eggs collected from beaches all over the world. All these different subspecies and populations of turtles were mixed in the tanks. Biologists fear that later generations of interbred turtles may have lost characteristics necessary for survival in the wild.
Educating the public about the impacts of using exotic animal products is key to the survival of sea turtles. Japan has long been a major user of turtle products, refusing to agree to international bans on trade.
Today, though, Japanese children are learning a different attitude toward sea turtles through bedtime stories. Japanese children are told an ancient Japanese folktale about the brave boy who rescues a sea turtle from abuse by other children. When the grateful turtle returns, the boy is handsomely rewarded for his compassion.
Question for Thought
Some scientists believe it is too late to save the Kemp’s ridley sea turtle, the world’s most endangered sea turtle. Although there are nearly a thousand Kemp’s ridleys alive, only a few hundred are females, from several different nesting beaches. Why would the low number of females be of particular concern?
Even though there are perhaps 100,000 leatherback sea turtles worldwide, their survival is threatened because geographically-distinct nesting populations do not interbreed with other populations. Can you think of any other endangered species in a similar situation?
What do you think of the idea of raising sea turtles on farms to provide shells and meat? Does this practice help or hinder the survival of wild sea turtles?
Words in bold italics can be found in the glossary.