Th e
leatherback turtle (Dermochelys coriacea) is the largest of all living
sea turtles and the fourth largest modern reptile behind three
crocodilians.It is the only living species in the genus Dermochelys. It
can easily be differentiated from other modern sea turtles by its lack
of a bony shell. Instead, its carapace is covered by skin and oily
flesh. Dermochelys coriacea is the only extant member of the family
Dermochelyidae. Instead of teeth the Leatherback turtle has points on
the tomium of its upper lip. It also has backwards spines in its throat
to help it swallow food. Leatherback turtles can dive to depths as great
as 4,200 feet (1,280 metres).
Leatherback turtles follow the general sea turtle body plan of having a
large, dorsoventrally flattened, round body with two pairs of very large
flippers and a short tail. Like other sea turtles, the leatherback's
flattened forelimbs are specially adapted for swimming in the open
ocean. Claws are noticeably absent from both pair of flippers. The
leatherback's flippers are the largest in proportion to its body among
the extant sea turtles. Leatherback front flippers can grow up to 2.7
meters in large specimens, the largest flippers (even in comparison to
its body) of any sea turtle. As the last surviving member of its family,
the leatherback turtle has several distinguishing characteristics that
differentiate it from other sea turtles. Its most notable feature is
that it lacks the bony carapace of the other extant sea turtles. Instead
of scutes, the leatherback's carapace is covered by its thick, leathery
skin with embedded minuscule bony plates. Seven distinct ridges arise
from the carapace, running from the anterior-to-posterior margin of the
turtle's back. The entire turtle's dorsal surface is colored dark grey
to black with a sporadic scattering of white blotches and spots. In a
show of countershading, the turtle's underside is lightly colored.
Dermochelys coriacea adults average at around one to two meters long and
weigh from around 250 to 700 kilograms. The largest ever found however
was over three meters from head to tail and weighed 916 kilograms. That
particular specimen was found on a beach on the west coast of Wales in
the North Atlantic.
Physiology
The metabolic rate of the leatherback is about four times higher than
one would expect for a reptile of its size; this, coupled with
counter-current heat exchangers, the insulation provided by its oily
flesh and large body size, allow it to maintain a body temperature as
much as 18°C (32°F) above that of the surrounding water. Its large size
also gives the leatherback more capacity to maintain its body
temperature than smaller, more ectothermic reptiles.Leatherbacks are
also the reptile world's deepest-divers. Individuals have been
discovered to be able to descend deeper than 1,200 meters (3,937
feet).They are also the fastest reptiles on record. The 1992 edition of
the Guinness Book of World Records has the leatherback turtle listed as
having achieved the speed of 9.8 meters per second (35.28 kilometers /
21.92 miles per hour) in the water.
Distribution
The leatherback turtle is a species with a cosmopolitan global range.
Of all the extant sea turtle species, D. coriacea has the widest
distribution, reaching as far north as Alaska and Norway and as far
south as the Cape of Good Hope in Africa and the southernmost tip of New
Zealand. The leatherback is found in all tropical and subtropical
oceans, and its range has been known to extend well into the Arctic
Circle. Globally, there are three major, genetically-distinct
populations. The Atlantic Dermochelys population is separate from the
ones in the Eastern and Western Pacific, which are also distinct from
each other. A third possible Pacific subpopulation has been proposed,
specifically the leatherback turtles nesting in Malaysia. This
subpopulation however, has almost been eradicated. The beach of Rantau
Abang in Terengganu, Malaysia, had once had the largest nesting
population in the world with 10,000 nests per year. However in 2008 only
2 leatherback turtles nested at Rantau Abang and unfortunately the eggs
were infertile. The major cause for the decline in the leatherback
turtles is the practice of egg collection in Malaysia. While specific
nesting beaches have been identified in the region, leatherback
populations in the Indian Ocean remain generally unassessed and
unevaluated.
subpopulation
Leatherback turtles in the Pacific Ocean have been determined to
belong to two distinct populations. One population is known to nest on
beaches in Papua, Indonesia and the Solomon Islands while their foraging
grounds are across the Pacific in the Northern Hemisphere along the
coast of Oregon in North America. The Eastern Pacific population forages
in the Southern Hemisphere, in waters along the western coast of South
America while they nest in beaches on the Pacific side of Central
America, specific nesting grounds being in Mexico and Costa Rica. The
Malaysian nesting population, reduced to less than a hundred individuals
as of 2006, has been proposed as a third major Pacific subpopulation.
There are two major leatherback feeding areas in the continental
United States. One well-studied area is just off the northwestern coast
of the United States near the mouth of the Columbia River. These waters
are excellent feeding grounds for the turtles, where they are believed
to be foraging in the nutrient-rich waters of the North Pacific. The
other American foraging area for the turtles is located in the state of
California.Further north, off the Pacific coast of Canada, leatherbacks
have been seen on the beaches of British Columbia.
Indian Ocean subpopulation
While little research has been done on Dermochelys populations in the
Indian Ocean, nesting populations are known from Sri Lanka and the
Nicobar Islands. It is proposed that these turtles form a separate,
genetically distinct Indian Ocean subpopulation.
Habitat
Leatherback turtles can be found primarily in the open ocean.
Scientists tracked a leatherback turtle that swam from Indonesia to the
U.S. in an epic 20,000-kilometer (13,000-mile) journey over a period of
647 days as it searched for food.The turtles prefer deep water but are
most often seen within sight of land. Feeding grounds have been
determined to be closer to land, in waters barely offshore. Unusually
for a reptile, leatherbacks can survive and actively swim in colder
waters; individual turtles have been found in waters as cold as 4.5°
Celsius.
The favoured breeding beaches of the leatherback turtle are mainland
sites facing deep water and they seem to avoid those sites protected by
coral reefs.
Trophic ecology
Adult Dermochelys coriacea subsist on a diet almost entirely composed
of jellyfish. Due to its obligate feeding nature, it has been
hypothesized that leatherback turtles play a role in the control of
jellyfish populations.Leatherbacks are also known to feed on other
soft-bodied marine organisms such as tunicates and cephalopods.
Dead leatherbacks that wash ashore have been studied to be veritable
microecosystems on their own while in the process of decomposition. A
drowned leatherback carcass observed in 1996 was observed to have been
host to sarcophagid and calliphorid flies after being picked open by a
pair of Coragyps atratus vultures. Infestation by known carrion-eating
beetles of the Scarabaeidae, Carabidae, and Tenebrionidae families soon
followed suit. After days of decomposition, beetles from the families
Histeridae and Staphylinidae and anthomyiid flies invaded the corpse as
well. All in all, organisms from more than a dozen families took part in
decomposition of the leatherback carcass.
Life history
Like all sea turtles, leatherback turtles start their lives as
hatchlings bursting out from the sands of their nesting beaches. Right
after they hatch, the baby turtles are already in danger of predation.
Many are eaten by birds, crustaceans, other reptiles, and also people
before they reach the water. Once they reach the ocean they are
generally not seen again until maturity. Very few turtles survive this
period to become adults. It is known that juvenile Dermochelys spend a
majority of their particular life stage in more tropical waters than the
adults. Adult Dermochelys are prone to long-distance bouts of migration.
Migration in leatherback turtles occurs between the cold waters in which
mature leatherbacks cruise in to feed on the abundant masses of
jellyfish that occur in those waters, to the tropical and subtropical
beaches in the regions where they were hatched from. In the Atlantic,
individual females tagged in French Guiana off the coast of South
America have been recaptured on the other side of the ocean in Morocco
and Spain.
Mating takes place at sea. Leatherback males never leave the water
once they enter it unlike females which crawl onto land to nest. After
encountering a female (who possibly exudes a pheromone to signal her
reproductive status) a leatherback male uses head movements, nuzzling,
biting, or flipper movements to determine her receptiveness. Females are
known to mate every two to three years. However, leatherbacks have been
found to be capable of breeding and nesting annually. Fertilization is
internal, and multiple males usually mate with a single female. However,
studies have shown that this process of polyandry in sea turtles does
not provide the offspring with any special advantages.
While the other species of sea turtles almost-always return to the
same beaches they hatched from, female leatherback turtles have been
found to be capable of switching to another beach within the same
general region of their "home" beach. Chosen nesting beaches are made of
soft sand since their shells and plastrons are softer and easily damaged
by hard rocks. Nesting beaches also have shallower approach angles from
the sea. This is a source of vulnerability for the turtles because such
beaches are easily eroded. Females excavate a nest above the high-tide
line with their flippers. One female may lay as many as nine clutches in
one breeding season. About nine days pass between nesting events. The
average clutch size of this particular species is around 110 eggs per
nest, 85% of which are viable. The female carefully back-fills the nest
after, disguising it from predators with a scattering of sand.
Cleavage of the cell begins within hours of fertilization, but
development is suspended during the gastrulation period of movements and
infoldings of embryonic cells, while the eggs are being laid.
Development soon resumes, but the embryos remain extremely susceptible
to movement-induced mortality in their nests until the membranes fully
develop through the first 20 to 25 days of incubation, when the
structural differentiation of body and organs (organogenesis) soon
follows. The eggs hatch in about sixty to seventy days. As with other
reptiles, the ambient temperature of the nest determines the sex of the
hatchlings. After nightfall, the hatchlings dig their way to the surface
and make their way to the sea.
As a global species with a range spanning both hemispheres,
leatherback nesting seasons vary from place-to-place. Nesting occurs in
February to July in Parismina, Costa Rica. Farther east in French
Guiana, Dermochelys populations nest from March to August.Atlantic
leatherback turtles nest between February and July from South Carolina
in the United States to the United States Virgin Islands in the
Caribbean and to Suriname and Guyana.[citation needed] With nearly
30,000 turtles visiting its beaches each year to April, Mayumba National
Park is the most important leatherback turtle nesting beach in Africa,
and possibly worldwide.
Evolutionary history
Leatherback turtles have been around in some form since the first
true sea turtles evolved over 110 million years ago during the
Cretaceous. The dermochelyids, as represented by the single living
species D. coriacea, are close relatives of the family Cheloniidae which
contain the other species of extant sea turtles. However, phylogenetic
analysis has determined their sister taxon to be the extinct family
Protostegidae which also included species with no hard carapace.
Etymology and taxonomic history
Dermochelys coriacea is the only species in its genus Dermochelys.
The genus in turn, contains the only extant members of the leatherback
turtle family Dermochelyidae.
The species was first described in 1761 by Domenico Vandelli as
Testudo coriacea. In 1816, the genus Dermochelys was coined by the
French zoologist Henri Blainville. The leatherback was then reclassified
under this own genus as Dermochelys coriacea.Later on, the species was
classified in its own family of Dermochelyidae in 1843 by the zoologist
Leopold Fitzinger. In 1884, the American naturalist Samuel Garman
described members of the species as Sphargis coriacea schlegelii. The
two described leatherback species were then united in D. coriacea with
each given subspecies status as D. coriacea coriacea and D. coriacea
schlegelii. The two subspecies were later rendered invalid synonyms of
the species Dermochelys coriacea.
The turtle's common name comes from the leathery texture and
appearance of its carapace. Aside from "leatherback" turtle, it has been
called the "leathery turtle" in the past. The turtle was also once
referred to as the "trunk" turtle, though the name is now in disuse.
Importance to humans
The harvesting of sea turtle eggs is still practiced by people around
the world. Asian exploitation of the turtle's nests have been cited as
the most significant factor for the species' global population decline.
In Southeast Asia, the collection of leatherback eggs has led to a
near-total collapse of local nesting populations in specific countries
like Thailand and Malaysia. Specifically in Malaysia, where the turtle
is practically locally extinct, the eggs are considered a delicacy. In
the Caribbean, some cultures consider the eggs of sea turtles to be
aphrodisiacs.
Conservation
Adult leatherback turtles are large animals that have few natural
predators. The most vulnerable stages in a leatherback's life are their
early life stages at which point they are most vulnerable to predation
of all kinds. Birds, small mammals, and other opportunists are known to
dig up nests and consume eggs. New hatchlings are also vulnerable on
their journey from nest to sea. Shorebirds and crustaceans are known to
prey on the turtles scrambling for the sea. Once they enter the water
they become prey to a whole new host of predators such as predatory fish
and cephalopods. Very few survive to adulthood.
Leatherback turtles have slightly fewer human-related threats than
the other sea turtle species. As their flesh contains higher oil and fat
content than other species', there is not much demand for their flesh.
However, human activity still significantly endangers leatherback
turtles in direct and indirect ways. Directly, a small amount of
leatherback turtles are caught for their meat by subsistence fisheries.
Nests are raided for eggs by humans in a few places around the world,
such as Southeast Asia. Aside from targeted efforts at catching adults
and collecting their eggs, there are many human activities that
indirectly harm Dermochelys populations worldwide. As a pelagic species,
D. coriacea individuals are occasionally caught as bycatch by commercial
fishing vessels. As they are the largest sea turtles alive today, turtle
excluder devices can be ineffective with adult leatherbacks of a
particular size range. It is reported that an average of 1,500 mature
females were accidentally caught annually in the 1990s. Pollution, both
chemical and physical, can also be fatal to leatherback turtles. With
their main diet consisting of jellyfish, many turtles die from
malabsorption and intestinal blockage following the ingestion of
balloons and plastic bags which resemble their prey.[5] Chemical
pollution has also had an adverse effect of the Dermochelys population.
A high level of phthalates has been measured in the yolk of D. coriacea
eggs.
Global conservation initiatives
It is also listed on Appendix 1 of the Convention on International
Trade in Endangered Species of Wild Flora and Fauna (CITES). This makes
it illegal to harm or kill the turtles.
Conservation of the Pacific and Eastern Atlantic leatherback
populations was included among the top ten issues in turtle conservation
in the first State of the World's Sea Turtles report published in 2006.
Specifically noted were the significant population declines in the
Mexican, Costa Rican and Malaysian populations. The Eastern Atlantic
nesting population was noted for being threatened by increased fishing
pressures from Eastern South American countries in whose waters the
leatherbacks forage.
The Leatherback Trust is an organization that was founded
specifically towards the aim of the conservation of all marine turtles,
specifically their namesake. The foundation was responsible for the
establishment of a sanctuary in Costa Rica, the Parque Marino Las
Baulas.
Country-specific conservation initiatives
As a species with a range encompassing dozens of coastal countries
around the world, the leatherback turtle has been subject to differing
country-specific laws regarding its conservation.
The United States has listed the leatherback turtle as an endangered
species since June 2, 1970. The protected status of the species (in
United States waters) was ratified with the passing of the U.S.
Endangered Species Act three years after. Farther north in Canada, where
the leatherback turtle can also be found, the Species Risk Act was
established to make it illegal to exploit the species in Canadian
waters. It has been classified endangered by the Committee on the Status
of Endangered Wildlife in Canada. Ireland and Wales have initiated a
joint leatherback conservation effort between the University of Wales
Swansea and University College Cork. Funded by the European Regional
Development Fund, the Irish Sea Leatherback Turtle Project as the
project is called, focuses on serious research programs such as tagging
and satellite tracking of individual leatherback turtles.
Several Caribbean countries have started conservation programs
focused on using ecotourism to bring attention to the plight of the
leatherback. On the Atlantic coast of Costa Rica, the village of
Parismina has one such initiative. Since 1998, the village has been
assisting turtles with a hatchery program.[43] Mayumba National Park in
Gabon, Central Africa was created to protect the most important
leatherback turtle nesting beach in Africa. More than 30,000 turtles
come to nest on Mayumba's beaches between September and April each year.
A more drastic measure that is being studied by the Malaysian
Fisheries Department is cloning. In mid-2007, the Fisheries Department
expressed a plan to clone leatherback turtles to replenish the country's
rapidly-declining Dermochelys population. Some conservation biologists
however, are skeptical of the proposed plan as cloning has been done
only on mammals such as dogs, sheep, cats, and cows, and uncertainties
persist about cloned animals' health and life spans. Leatherbacks used
to nest in the thousands on many of Malaysia's beaches, including those
at Terengganu where more than 3,000 nesting females were counted in the
late 1960s. The last official count of nesting leatherback females on
that beach was recorded to be a mere two females in 1993.
In Brazil, reproduction of the leatherback turtle is being assisted
by the IBAMA's "projeto TAMAR" (TAMAR project), which aims to protect
all sea turtles in the Brazilian coast, by assisting their nests and
preventing accidental kills by fishing boats. The last official count of
nesting leatherback females in Brazil was recorded to be only seven
females.
It is listed as Vulnerable under Australia's Environment Protection
and Biodiversity Conservation Act 1999, and as Endangered under
Queensland's Nature Conservation Act 1992. |
