(mellow music)
- [Narrator] Sea turtles
are ancient mariners.
Present in all but Earth's coldest oceans,
these marine reptiles are well-adapted
to a life on the move.
(dramatic music)
Sea turtles have existed since
the time of the dinosaurs.
The earliest known marine turtle
lived about 120 million years ago.
Named Desmatochelys padillai,
it was six feet long
and had the characteristic
features of modern sea turtles
including a carapace, or a top
shell, and paddle-like limbs.
Today, there are seven
species of sea turtles
with the largest being the leatherback.
Growing as long as eight feet
and weighing up to 2,000 pounds,
it is larger than known fossils
of its prehistoric ancestor, the padillai.
Sea turtles can lay more
than 150 eggs at a time.
Called the clutch,
these large egg deposits
help ensure the survival
of sea turtle hatchlings.
Once a female lays her eggs,
she returns to the sea,
leaving her hatchlings
to fend for themselves.
Fewer than .1% of hatchlings
survive to adulthood
in part due to numerous
predators on the beach.
Emerging in large numbers
increases the chance
that some will survive.
(waves crashing)
A sea turtle's sex is
determined by temperature.
Unlike most vertebrates,
a sea turtle's sex
is not determined by sex chromosomes.
Instead, the temperature of the nest
determines the sex of the hatchlings.
When temperatures are warm, at
about 88 degrees Fahrenheit,
most of the hatchlings will be female,
but when temperatures are cooler,
less than around 82 degrees Fahrenheit,
most of the hatchlings will be male.
(mellow music)
Sea turtles use Earth's
magnetic fields to navigate.
Sea turtles have geomagnetic abilities
which serve as an internal GPS.
The turtles have particles of magnetite,
a magnetic mineral, in their brains.
The magnetite likely plays a role
in orienting sea turtles
to Earth's magnetic poles,
similar to a compass.
Baby sea turtles imprint on
the unique magnetic signature
of the beaches where they hatch.
This magnetic map can guide them
back to the same beaches
several years later
to lay their own eggs.
(mellow music)
All seven sea turtle species
are threatened with extinction.
Once abundant, sea turtle populations
have dramatically declined
in the past two centuries.
Fishing is a major threat to sea turtles
as they become caught in fishing nets
as bycatch, or accidental catch.
Illegal harvesting of turtle eggs,
trafficking in turtle products,
and ocean pollution are also concerns.
However, policies have been enacted
to reduce bycatch,
protect turtle habitats,
and prohibit the killing of
sea turtles and their eggs.
By continuing this kind of intervention,
humans can help stop the
decline of sea turtles,
helping keep these ancient
mariners in the world's oceans.
(waves crashing)
