The leatherback sea turtle is the largest living turtle in the world and, due to its being so distinctive, is placed in its own taxonomic familyóDermochelydae. Hence, its name is Dermochelys coracea. It is 4 to 6 feet in length and weighs 800-1300 lbs. as an adult.
Its diet consists mainly of jellyfish and marine planktonic creatures, but it also feeds on green algae, hydrozoa, octopuses, and eggs. It does not have teeth but uses its jaws, which are sharp edged but not particularly strong, to tear and crush its food. They have 2-3 in. long backward spines that line the mouth cavity and cover the esophagus. Some scientists believe these are a special modification for a diet of slippery prey like jellyfish.
Speaking of eating, the leatherback can be poisonous when eatenóone of two turtles toxic to humans and other animals. Its flesh is extremely poisonous and its chemistry is unknown. Eating it can cause nausea, vomiting, diarrhea, burning sensation, tightness of chest, difficulty swallowing, hypersalivation, foul breath, skin rash, coma, and even breath. So, donít!
The leatherbackís "shell" is about 1 ½ in. thick and is composed of tough, greasy cartilage. Just under the surface of the caprice is a layer of thousands of small, polygonal bones forming a mosaic. It is covered with rubbery, leathery skin that is somewhat flexible to the touch. It has no scales on its skin, except in youngsters, but has 7 longitudinal ridges or keels which divide the carapacial surface and help to provide some rigidity. The neck is short and incompletely retractable, as sea turtles can not bring tier head inside their shells. The leatherback is rather barrelshaped. The shell grades almost imperceptibly into the neck and shoulder region. Its front flippers are clawless and extremely long and may span as much as nine feet. The hind flippers are broad and connected to the tail by folds of skin. The tails of males are longer than their hind limbs and females barely half as long. The leatherback is black or dark brown with white or light pink splotches; frequently white spotting is very dense.
The most massive bones in the leatherback are the scapulae and the thick humeri; it is to these bones that the massive swimming muscles attach. A peculiar feature of the leatherback skeleton is its retention of essentially embryonic characteristics into adult life. The limb bones retain extensive cartilaginous ends. The skeleton is also suffused with oil that is composed largely of polyunsaturated fatty acids. It could be possible that the oil functions in lessening decompression problems during rapid diving and re-surfacing, but is rather unlikely that its function is to increase buoyancy. The oil is used medicinally in the Virgin Islands and as boat sealant as well as in cosmetics elsewhere. There is no known way to determine their age, and age at sex maturity is unknown.
The leatherback is the greatest wanderer, reaching the most poleward latitudes. It can be found from Norway to New Zealand. They range throughout the Atlantic, Pacific, and Indian Oceans from Iceland, the British Isles, Alaska, Japan, south to Argentina, Chile, Africa, the Mediterranean, and, of course, Costa Rica!
Leatherbacks spend their time out at sea at the depths of the oceans. They frequently come to the surface to breathe when active but can remain under water for several hours while resting. Leather backs can dive more than 3,000 feet. It is very rare that juvenilesóthose between hatchlings and adults are ever found. Adults remain in the ocean deeps except when nesting. The leatherback is completely unable to cope with obstacles in its path; in captivity, whether it be in land or water, it bashes itself into the walls of the container until it kills itself. The only place where such an animal would be able to survive is in the open ocean. The way it is able to cope with its deepwater habitat is by maintaining a body temperature considerably higher than that of its surrounding environmentó18 degrees Celsius higher in some experiments. Its large size ensures a small surface to volume ration. Moreover, the shell and fatty skin acts like a layer of blubber in insulating the body; this is called "gigantotherapy." Also, the countercurrent system in the limbs permits homeotherapy. The oil may also retard heat loss.
The nesting behavior of the leatherback is the only aspect of the turtleís life that is well known. They rarely nest on islands and areas that have coral or jagged rocks due to the fact that the skin of the leatherback is so tender. They may even suffer multiple minor lacerations just from moving along the sandy beach. Nesting takes place at night and may nest several times (possibly as many as nine) in the course of a season at intervals of about ten days. The average inter-nesting interval is shorter than any other turtleís. It is thought that the leatherback nests in alternating years, with a very small number nesting in successive years or in three year intervals. The nesting season is typically from March to July in the southern hemisphere and from October to February in the northern. Nesting season begins in the late part of the wet season so that when the babies emerge the rainy season is over and the sand is dry.
The nesting leatherback is imperturbable. They are not bothered by lights, noises, or rain; whereas, most turtles avoid very rainy nights. They can be tagged during their trip back to shore and not interrupt the nesting sequence.
The leatherbacks emerges from the sea at night, usually at high tide. They seek out areas that are free from rocks, wood, vegetation, and other debris and that have a gentle slope. The track up to the beach is usually a sinusoidal track in order to lessen the slope the animal has to climb because it is ponderous and clumsy on land. While moving on land, the leatherbacks emit loud groans and belches. The female digs a hole in the ground with her rear flippers. She excavates about 70cm. Simultaneously, she uses her hind flippers to pile up the sand for covering the eggs later. As the hole gets deeper, the female lifts her head and supports her weight with her fore flippers, a position which lowers the hind flippers, allowing them to dig deeper. She uses her flippers as scoops and lifts the sand out and then flings it backward from the hole. The pit, when complete, is bottle shaped and generally deeper than that of other turtles.
She then lays the eggs, usually two to three at a time from the extruded cloaco, along with a great deal of mucus. Leatherbacks lay about 70 large fertile eggs and 40 small infertile ones. These infertile eggs are undersized, yolkless, and malformed. They usually average 20-40% of the number of normal eggs. There are several theories as to why they lay so many infertile eggs. Since the infertile eggs are deposited last on top of the normal ones, it is thought the infertile ones could offer protection from the sun or possibly provide nutrients to the eggs below as they can interchange nutrients and gasses such as oxygen. However, the most likely possibility is that they decrease predation as the predator would uncover and consume the infertile eggs and, hopefully, leave the eggs with embryos in the nest. The eggs are leathery and bounce as they fall into the hole. After the laying of the eggs is completed, the turtles fills in the nest with her hind flippers and scatters the sand with her fore flippers. Turtles cover the eggs to protect from surface predators; to keep the soft porous shells moist and prevent desiccation; and to maintain the temperature of the eggs. The female continues to scatter sand as she returns to the water to obscure the nestís location. An idiosyncrasy of the leatherback is that it turns a complete circle or several circles after completing the nest. This could be to orient herself towards the sea. The leatherback is usually on shore for 1 ½ - 2 hours.
The eggs are little more than two inches in diameter and take about 60-70 days to hatch. It is believed that sane temperatures play a key role in determining both the timing of the hatchlings emergence and the sex of the hatchling. The lower the temperature the eggs are placed in, the more males are produced. Higher temperatures produce more females. Hatchlings use a caruncle, a temporary egg tooth, to help break open their shells. It normally takes 3-7 days to reach the surface. When the hatchlings do emerge, it us mainly at night and in groups.
Baby leatherbacks turn in "orientation circles" as they head for the sea, as do the adults. There are mainly two theories as to how the hatchlings are able to find the sea. Some scientists feel that the turtles discriminate the light intensities and head for the greater light intensity of the open horizon. Others think they have an internal compass which they use to navigate away from the shore and into the sea. It would be this same compass that is set by way of the poles that ingrains itself into the turtles as to their exact location in order to return to nest.
The hatchlings are about 2 ¼ inches in carapace length and 446 grams in weight and are similar to adults in appearance, though the fore flippers are proportionally longer and both shell and skin are covered with small scales. These scales are lost in a couple of months. The baby is marked with pure white along the carapace ridges and flipper margins, but this later turns to random spotting.
Once they reach the surf, the babies dive into a wave and ride the undertow out to sea. Many terrestrial and ocean predators devour the hatchlings, for it is thought that only between 2-5% survive their first few days of life and only . Once reaching the water, the turtles undergo a 24-48 % reach maturity. Once reaching the water, the turtles undergo a 24-48 hour "swim frenzy" of continuous swimming. They strive for the deeper water where they are less vulnerable and have been seen to dive straight down to avoid bird predation. The first year of the turtleís life is called the "lost year" because we are not sure what they do or where they go. They believe that they ride the prevailing currents, situating themselves in the floating seaweed called drift lines which are rich in food and provide hiding places for the juvenile turtles. They spend their first years in an oceanic existence before coming to coastal shores. If they can make it past the juvenile stage, they enjoy about an 80% or more survival rate. There is no known way to determine their age, though.
There are many threats to the leatherbacks. The eggs, being unguarded, fall prey to predators such as crocodiles, lizards, raccoons, ghost crabs, and armadillos, to name a few. The adults have few natural enemies at sea but have been found in the stomachs of sharks and whales. A few nesting leatherbacks have been killed by jaguars. Nature also causes the loss of the leatherbacks. Such things as heavy rains, erosion, and inundation (drowning) of nests either form the rain or from the tides cause the death of hatchlings. Still, the main threat to leatherbacks is man.
Its eggs are a major source of protein and exploited for their food value. Other leatherbacks are slaughtered for their meat or caught by fisherman for their oils which can be used in such products as cosmetics and to prevent impotency. However, the leatherbacks are not frequently trade is not a lucrative business and the endangerment of the leatherback is not mainly due to the commercial fishing industry specifically. Leatherback turtles are killed by incidental capture in shrimp trawls, oil dredging expeditions, boat collisions, during the removal of oil rigs, and from being entangled in lost or discarded fishing gear or debris. They become entangled in longlines, fish traps, buoy anchor lines, and other ropes and cables, causing serious injury or death by drowning. Many deaths also occur due to the ingestion of plastics and other trash such as styrofoam, balloons, and plastic bags that the turtles apparently mistake for squid. Deaths also result from accumulation of toxic substances like the ingestion of petroleum residues. Respiration, skin, blood chemistry, and salt gland functions are affected by oil spills.
There are several things that cause the decline of the leatherback population that are the result of manís attempt to improve beaches. Such things are the result of coastal development and other activities that are the byproducts of human life. Beach armoring occurs from beach front development whose sight is fortified to protect the property form erosion. These can include such things as sea walls, rock revetments, sandbags, and jetties. This can result in a permanent loss in dry nesting beach area as well as preventing or deterring females form reaching suitable nesting sites. They can also cause false crawls by the hatchlings as well as trap them. Beach nourishment is the pumping, trucking, or depositing of sand on the beach to replace what has been lost due to erosion. Such attempts at improvement can disturb nesting sites or turtles as well as bury existing nests. Pipelines and other machinery used create barriers to nesting females and hatching leatherback babies. Artificial lighting is another major problem for both adult and baby turtles. It causes disorientation and misorientation. Turtles are attracted to light so the hatchlings can forego their run to the ocean and head towards the light, increasing their chances of being eaten by predators, be entrapped in debris or vegetation, or increase their chances of desiccation. Some hatchlings will even come out of the surf to pursue lights. Finally, beach cleaning methods to remove debris by raking or hand picking affects the hatchlings. Heavy machinery moving across the nests can either compact, uncover or destroy them. Tracks both hinder and trap the hatchlings.
The mere presence of man is another obstacle for the leatherbacks survival. The utilization of beaches by tourists can disturb the females and the nests. The use of off-road vehicles on the beach is a serious problem in many areas. They can squish the nests and the hatchlings. Tire ruts also interfere with the ability to reach the ocean.
Luckily, man is also the leatherbackís friend and is working to save the endangered turtle. The Leatherback is listed in Appendix I of the Convention on the International Trade in Endangered Species, the Bonn Convention of the Conservation of Migratory Species and Wild Animals, and on the IUCN (World Conservation Union) Red list of endangered species, and listed in the Endangered Species Act, just to name a few. There have been numerous conferences and efforts to try and conserve the depleting leatherback population. Sadly, there are only 20,000-30,000 female leatherbacks left in the world.
In the 1980s a legal battle was fought to force US shrimping fleets to install special devices called TEDs, Turtle Exclusion Devices, to keep sea turtles from being killed in nets dragged by trawlers. They are designed to divert turtles but allow smaller catch to pass through. There are two basic types: a grid made of metal and a barrier made of netting. Although the TEDs are required and failure to use them can result in major fines, turtles are still being ensnared. Some fisherman just refuse to use them while others use the "soft" devices made of netting and do not work. The US has attempted to track down such violators within the US as well as abroad. Those that lack TEDs drown thousands of turtles annually. Traditionally, leatherbacks are larger than the escape openings of most TEDs so they are not an effective means of protection. Therefore, because of the ineffectiveness in the US waters especially to prevent turtle deaths, the government called for several measures to be taken by the shrimping industry in order to save the leatherbacks. These options included: closure of areas to all fishing, use of restricted tow times, mandatory observers on the lookout for leatherbacks, or the use of TEDs with escape openings large enough to exclude leatherbacks. The National Marine Fisheries Service conducts aerial surveys weekly to monitor the leatherback population. If the surveys indicate a large presence of the leatherbacks, they prohibit shrimping. Those boats that have approved TED devices are allowed to shrimp but must registering before doing so and provide reports as to the sighting, activity, and capture of all leatherbacks. Other actions the US has taken against the fishing industry is to stop the importation of wild shrimp from Thailand, Malaysia, Pakistan, India unless the shrimp were caught in ships fitted with TEDs.
There are also other actions being taken by communities and scientists around the globe to protect and study the great leatherbacks. Among such possibilities as the regulation of the shrimping industry are the use of park officials to control all activities on the beach, the elimination of white lights that shine on the beach, the restriction of tourism, the clearing of the beaches from debris, and the operation of hatcheries to aid in study and preservation of the leatherback babies. Such hatcheries would work to preserve the nests from predators and tides. There has also been a movement towards the use of screens to deter predators from the nests. Wire screens are secured over the buried nests and are the most effective ways to keep raccoonsóthe major threat to leatherback nestlingsóout. It is more effective than routine killing of the raccoons at the nest sites. The screens are three foot by three foot mesh that have openings two to nine inches. The screens are stretched over the nest and secured by three feet of rebar pounded into the sand. In some places, volunteers remove the screens a week before the hatchlings are ready and patrol the beach. In some places, this has reduced predation from 95 to 15%. However, such a means of protection depends upon the effort and volunteers.
There is also another program dubbed "Head Start" that captures newborn turtles along the beach and raises them in captivity. This is a very controversial program; it is a hit with the public but scorned by most scientists that feel that such actions disrupt the migration patterns of the turtles which are still inefficiently understood. It interferes with the so called crucial "imprinting" process of the hatchlings. As the baby leatherbacks swim offshore in the first few days, they acquire a kind of internal compass using the earthís magnetic field which they use later to return to lay their eggs. Head Start turtles are denied the imprinting step, which means they may never return home to nest. Also, the captured turtles may bring diseases out into the wild populations. Head Start turtles have even swam up to humans looking for food. Therefore, the best solution is to enable the turtles to survive in their own natural environment, following the process of nature. Such conservation alternatives would be the alternative discussed previously.
Another essential feature in the preservation and study of the leatherbacks to tag the leatherback females when they emerge on shore to lay their eggs. Tags enable scientists to monitor the movements and actions of the elusive leatherback. They also enable workers to count and record the number of times a female returns to nest in a season or in successive seasons. Additionally, tags allow scientists to study the progression of the leatherback population.
Many scientists mark turtles with the same PIT (Passive Integrated Transponders). There has been a movement for scientists to use compatible PIT tag readers. This would not only aid the scientists in learning more about the lifestyle and migration of the leatherbacks that would aid in the ability to protect them. Such tracking devices allow investigators to track the turtlesí movements in relation to the fishing boats, which would be valuable information.
There has been new hope in tagging the leatherback turtle that was just developed recently. Scientists at a New England Aquarium developed a satellite tag more suitable for the leatherback. Traditional methods of attaching transmitters with epoxy do not stick to the leatherbacksí rubbery and oily shells. As a result, scientists have been forced to use custom-fitted harness backpacks with a cumbersome floating device. The newly developed tag uses mini-bone anchor screws to attach the satellite tag to the leatherback. It implants a tiny bio-degradable screw, threaded with suture material though the shell into the tissue underneath. The sutures fasten a cell-phone sized satellite transmitter to the top of the turtles shell, and the screws disappear after a few days. The tag transmits data on location, and depth and time of dives. This new tag, if successful, would allow scientists to track males and juveniles that donít come ashore as well as the females but are mainly designed to enable researchers to understand the migration paths of leatherbacks as well as their activities in the open ocean. This would open the way to greatly reducing the number of leatherback moralities in the sea from fishing boats. Maybe there is a bright ray of hope for the rescue of the leatherback sea turtle from endangerment after all.
If you care to research more about the leatherback sea turtle, here are some of the sources I used to garner my information:
Beletsky, Les. Ecotravellerís Wildlife Guide to Costa Rica. Boston: Natural World Academic Press, 1998.
Bjorndal, Karen A., ed. Biology and Conservation of Sea Turtles. Washington: Smithsonian Institute Press, 1997.
Carr, Archie. So Excellent a Fishe: A Natural History of Sea Turtles. Garden City: Natural History Press, 1967.
Ernst, Carl H. and Roger W. Barbour. Turtles of the World. Washington: Smithsonian Institute Press, 1989.
Lutz, Peter L. and John A. Musick, eds. The Biology of Sea Turtles. Boca Raton: CRC Press,1997.
Harless, Marion and Henry Morlock, eds. Turtles: Perspectives and Research. New York: Wiley, 1979.
Pritchard, Peter C. H. Encyclopedia of Turtles. Neptune: T.F.H. Publications, Inc., 1979.
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