An enormous leatherback sea turtle surfaces for a breathe of air.
Photo - Courtesy of Vidal Martin, SECAC
May 18, 2005
Leatherback Sea Turtles
This is Judith Scott speaking to you from the Odyssey in the Atlantic Ocean.
Having left the waters of the Canary Islands, where loggerhead sea turtles (Caretta caretta) sightings were an almost daily occurrence, we are yet to sight any during
our Atlantic crossing. Towing our acoustic array and with at least one crew member aloft on observation watch throughout the daylight hours in our constant search for
sperm whales, we hope to get a glimpse of another great, open ocean wonderer, the giant, one ton leatherback sea turtle (Dermochelys coriacea).
Of the seven types of sea turtle; the leatherback is by far the largest. It is so different from all the other species of sea turtles that it is classified in a separate
family, the Dermochelyidae. This exceptional reptile can reach lengths of at least 8.4 feet (256cm) and a weight of one ton (1000 kilograms). Their flippers alone can be
3.3 feet (1m) long and instead of having a hard shell like other sea turtles, they have a leathery skin on their backs. The leatherback dives deeper, goes into colder water
and travels farther than any other species of sea turtle.
The leathery skin is obviously what gives the leatherback its common name. It is composed of thick oily, cartilaginous material which underneath is strengthened with
thousands of very small bones. The species has seven narrow ridges that run the length of the carapace, which is a characteristic of most sea turtle hatchlings, but in
other species, these ridges are lost in adulthood. Leatherbacks are also the only species that have no claws or scales on their flippers.
One of the most incredible things about these record-breaking reptiles is their food source. Leatherbacks feed almost exclusively on jellies. Diving to depths of 3,300 feet
(1000 meters) or more, they are rivaled only by sperm whales, beaked whales and elephant seals, as air breathing animals that can go to extraordinary depths. What is
most remarkable about this diet is the fact that jellies are 95% water and somehow leatherbacks manage to grow faster and larger than any other species of sea turtle,
on these creatures alone. Jellies do contain protein, but to receive enough energy for their daily requirements, scientists have calculated that leatherbacks need to consume
their entire body weight in jellies each day. The jellies they eat are found in the deep scattering layers. These are layers of small, mid-water animals that migrate
vertically at night, coming close to the surface during darkness. Leatherbacks have to feed day and night to obtain enough food, diving deep during the day and then taking
advantage of the shallower scattering layer at night.
Veternarian Dr. Pascual Calabuig Miranda with a stranded leatherback sea turtle in the Canary Islands.
Photo - Courtesy of Dr. Pascual Calabuig Miranda
Leatherbacks nest on beaches around the tropical parts of the Indian, Atlantic and Pacific Oceans but migrate up to 3100 miles to areas in the temperate zones, such as
Canada in the north and Australia in the south, to feed. Like all sea turtles the females come onto the beaches a number of times over a period of a few weeks to nest.
They lay between four to seven clutches per season at nine to ten day intervals. Leatherbacks lay more clutches and at shorter intervals than other species of sea turtles,
but this has not improved their chances of survival in the modern world.
Unfortunately this species seems particularly susceptible to human impacts, even though all species of sea turtles are classed as vulnerable or endangered. All turtle
hatchlings face a huge array of problems before they grow large enough to be safe from most big predators. Crabs, birds, fish and sharks all prey on hatchlings, and they
also face human impacts on nesting beaches, such as eggs being taken, nests destroyed and lights that confuse the hatchlings. It is estimated that only about 1 in every
1000 hatchlings born survives to become an adult. For this reason it is extremely important to the survival of all sea turtle species, that the adults are not killed in
large numbers, but this is unfortunately what is happening with the leatherback.
In the Pacific the numbers of leatherbacks has declined by about 95% over the last 22 years. Experts fear that on the Pacific coast of the Americas, the population of
reproducing females has plummeted from 91,000 in 1982 to fewer than 3,000 now. Based on this level of decline, scientists are predicting Pacific leatherback turtles could
be extinct within the next 10-15 years. Certain types of fishing practices are wiping out these magnificent creatures that have survived for over 100 million years.
The main culprit is longlining. This fishery is primarily for tuna and swordfish where the boats lay down 40-60 miles of vertical lines with baited hooks at a time.
This equates to about 3,000 hooks a night for each vessel, which is somewhere around 1.5 billion hooks in the world's oceans per year, or 4.5 million a night, according to
a study by the Pew Charitable Trusts. All turtles and many other non-target species get entangled or caught using this method of fishing, but it appears leatherbacks are
particularly vulnerable to entangling in fishing line. It is believed this is in part due to their long flippers and the way they swim.
The leatherback turtle, as with all other sea turtles is also affected by the phenomenal amount of trash that humans dump into the oceans. Plastic bags resemble jellies in
the water, the leatherbacks favorite food. Rubbish, and particular plastics, that take centuries to biodegrade, are adversely affecting all animals in the oceans but for
leatherbacks this is an acute problem. Turtles are found with their stomachs full of plastic, meaning they will gradually starve to death.
Leatherbacks have been seen in Canaries waters, sometimes alive and sadly on occasions as dead animals that have washed up on a beach. They are a lucky and rare sight here,
as in most areas of the world.
Dr. Pascual Calabuig Miranda examines a dead leatherback sea turtle at the Centro de Recuperacion de Fauna -
Silvestre de Tafira on Gran Canaria.
More than 200 turtles, are brought to the rehabilitation hospital every year as a result of entanglement in fishing nets, swallowed hooks,
ingested plastic, boat strikes and oil spills.
Watch a special video report about the Centro de
Recuperacion de Fauna.
Photo - Courtesy of Dr. Pascual Calabuig Miranda
The Odyssey crew has only seen a leatherback once in their entire five-year global voyage, in the western Indian Ocean. I have been lucky enough
to see a leatherback at close range, off Western Australia. At first I believed it might be a small whale, but then a huge black head emerged above the surface for a breath,
and I realized it was a huge leatherback turtle. The turtle appeared to be rather curious and approached the vessel. It stayed with us for a handful of breaths, and then
commenced its journey into the depths, disappearing into the murky water. It left me spellbound, an experience I know I will never forget.
The only way we as a species can insure the survival of this magnificent and record breaking creature is to make educated choices in our lives to help protect them.
These include making sure we dispose of rubbish properly, particularly plastic bags that resemble jellies when floating in the ocean. We can also make consumer
choices with the fish we eat, choosing species that are not caught using long lining, which are usually targeting tuna and swordfish. Leatherback sea turtles have
survived for millions of years, diverging from the other species of sea turtles in the Cretaceous period, over 65 million years ago, but they now may only have a
couple of decades left. Scientists are predicting that the Pacific leatherback could go extinct within the next 10 years, a rather sad reflection on the
impacts we are having on the environment.
The crew of the Odyssey would like to thank Dr. Pascual Calabuig Miranda of the Centro de Recuperacion de Fauna - Silvestre de Tafira on Gran Canaria
and Vidal Martin of SECAC for their assistance with this report.
Log written by Judith Scott.