The Project
Some biology of the Leatherback Turtle.
Leatherback sea turtles are the largest living marine reptiles
and live almost their entire lives at sea. The only times that
they are on land is when the female turtles lay eggs, and when
hatchlings emerge from the nest and make their way to ocean. We
estimate that they are sexually mature at about 10 years or age
and may to live to be 40 years old. Studying their biology is
very difficult due to the nature of their intermittent visits
to land, juvenile and male turtles are almost never seen at all.
Consequently, most studies and protection efforts have focused
on nesting females and hatchlings.
Leatherback turtles are different to other sea turtles in that
they have a soft, cartilaginous shell rather than a hard bony
one. It is from the appearance of the shell that the "Leatherback"
name comes. They have a more streamlined shape and larger flippers
than other sea turtles, reflecting their more migratory and pelagic
lifestyle.
This turtle has a shell about 170 cm long,
and weighs about 300 kg.
The life cycle of Leatherback turtles
Nesting
When the female turtles come ashore to nest, they choose beaches
which have particular types of conditions. They are generally
free from rocks and have a gentle slope. The turtle emerges from
the ocean at night, usually close to the high tide and crawls
up the beach until she is above the high tide mark. There she
selects a site free from wood, vegetation and other debris and
digs a pit for her body. She does this by throwing sand with powerful
strokes of her front flippers until her body sits in the hole
created.
Crawling up the beach is a slow and tiring process. The body
pit is dug with the front flippers.
Then with her rear flippers she delicately excavates a chamber
about 70 cm deep for the eggs. The sand must be of the right texture
so that the nest cavity doesn't collapse while it is being dug
. She alternates with her rear flippers to reach into the hole
and scoop out the sand which is then flicked to the side. When
the hole has been dug as deep as the flippers will reach, she
starts to lay.
Carefully reaching into the hole to scoop out more sand. The
eggs are leathery and bounce as they fall in.
During the period when the eggs are being laid, she becomes very
unresponsive to her environment and this is typically when biological
information is collected. About 70 large, fertile eggs and 40
small infertile eggs are laid, the function of the smaller eggs
is not clear. The turtle then gently packs sand into the hole
with her rear flippers and disguises the location of the nest
by throwing more sand with her front flippers, possibly to hide
he location of the nest from predators of the eggs.
The sand is gently pressed back over the eggs. A lot of sand
is thrown when covering the nest.
With the nesting process complete, she returns to the ocean about
2 hours after she first emerged and takes no further part in care
of the eggs or hatchlings. Female turtles nest on average 7 times
in the season, at intervals of about 9 days.
The entire nesting process is a big physical
effort.
Development and Hatching
The incubation period is around 60 days, and the temperature of
the surrounding sand determines the sex of the hatchlings during
a critical phase of embryonic development. At Playa Grande, temperatures
above 29.5 degrees C produce female hatchlings, while below 29.5
C the hatchlings are male. The hatchlings break out of their eggshells
under the sand and begin to dig their way to the surface, to emerge
in groups at night. The crawl to the water is a dangerous time
for the hatchlings, but it may also play an important role in
allowing them to "fix" the location of where they are
so the females can return there to nest as adults. We have very
little information on what happens to the hatchlings after they
enter the ocean, but very few survive to become adults, perhaps
only a few in a thousand.
As the hatchlings reach the surface they slowly break through
the sand and emerge in a group.
At the surface they struggle to pull themselves free so they
can head for the water.
Although they come out in a group, the hatchlings don't stay
together as they crawl to the water's edge.
Life at sea
We know very little about the life of leatherback turtles
after they leave the beach as hatchlings. They appear to migrate
long distances between feeding and nesting areas. Their main diet
is jellyfish and leatherbacks have special spiny structures in
the oesophagus to trap them there. They have remarkable diving
abilities and are able to dive below 1400 metres and to remain
submerged for nearly an hour. Useful information is being gained
by satellite tracking of adults to try and determine their migration
routes.
Leatherbacks are extremely powerful swimmers, with all the
work done by the front flippers while the rear flippers aid in
steering. This turtle had a satellite tracker attached to it for
a short time.
