Let's Talk About Sea Turtles! If you’ve seen Finding Nemo you might think
sea turtles can live for a hundred-something years, and know that the babies are adorable, but
there's a lot more to a sea turtle’s life cycle There are seven species of sea turtles: hawksbill,
olive ridley, kemp’s ridley, flatback, the enormous leatherback, loggerhead and the green
sea turtle. Each species has their own life cycle but, we’ll focus on the family as
a whole, instead of the individuals. We’ll start at stage 1, the eggs. Every
2-4 years, pregnant mothers crawl on the beach, bury a pit in the sand and lay their eggs.
They cover up the pit, head back to sea and after 6-12 weeks, poof! Adorable baby turtles
are cracking their shell, wiggling out of the sand, and hilariously flapping their flippers
across the beach. While this is cute, don't get too attached
because 99% of these turrtles won't make it to adulthood. Almost all will perish in this
tough journey ahead. Once the babies emerge from the shell, they typically wait until night, when there are less predators and the sand is cool enough to crawl across. Once
they’re through the sand they look for one signal, the moon's reflection off the ocean.
This behaviour is innate - it’s an instinct. There’s no thinking, it’s the hatchlings
urge to head towards the light because that leads them to the ocean. If you've seen a sign warning you about street
lights being turned off near the beach it's because there's a sea turtle spawning site
nearby. Artificial lights can confuse the hatchlings and lead them towards streetlights,
house lights or headlights which would all lead to… yeah. The lucky ones who aren’t fooled crawl as
quickly as they can to the sea, hoping raccoons, crabs and birds don’t gobble them up for
an easy snack. They're in the ocean. Great! Right? Well… not exactly. It's not like the ocean is that safe either. The moment the hatchling touches the water it begins
the 'frenzy' period. What's the frenzy? Twenty. Four. Hours. Of straight swimming. Imagine being the size of the palm of your
hand, being dropped into the ocean minutes after birth, and now you have to swim and
not stop. If you stop you’re dead, if you don’t stop.. You’re probably also dead...
The shallow water is littered with animals that would love to eat a tender hatchling,
or 10. So, now what? The small juvenile stage is
where the research is scarce. As you might imagine, trying to put a tracking device on
a sea turtle that transmit signals, never runs out of battery and doesn’t fall off,
all while not affecting the turtle’s buoyancy or ability to swim might be difficult. Because
of this, these years are called "the lost years” but with technology getting better,
these years are becoming more known. It's clear that the turtles use currents. It was
first thought to be passive migration - unintentionally following currents but more evidence is showing
sea turtles actively orient themselves and swim. The best research suggests sea turtles detect
the earth’s magnetic field and use it as a compass, a really really accurate one, to
navigate the oceans. While the complexity of this goes beyond the scope of this video,
it’s important to understand sea turtles have a sense we don’t have called magnetoception
and this sense becomes very important for turtles later in life. Until then, once turtles grow to be large
juveniles they head to their feeding grounds in coastal waters. These can be over ten thousand
kilometers away from their home beach. In the feeding grounds turtles grow to be sub-adults,
and once they’re ready to mate they’re mature adults, and it’s time to start migrating
back to the nesting sites. During the migration a male will mate with as many females as possible to pass on as much of his DNA as he can, while a female will store as much sperm as she can
because more fertilized eggs means more offspring which means more survivors. After mating, males travel back to the feeding
grounds while females continue to the beach. At the beach the females lay their eggs and
we’re back at stage 1. The soon-to-be mother’s travel back to the feeding grounds until the
next mating season. But what’s interesting is that the mothers usually lay their eggs
on the exact same beach where they were born. This is natal homing and how it works isn’t
fully understood. The best explanation is geomagnetic imprinting.
When they’re born hatchlings imprint on the magnetic field of the earth and use this
unique signature to guide them home decades later. But.. why? Why go back to the exact
same beach? It’s a fair question, because traveling ten thousand kilometers to reproduce
doesn’t seem ideal. You’re risking death, expending tons of energy and are probably
closer to some perfectly good nesting sites. But we know that natal homing must have benefits-
or at least outweigh the risks for the animals to adapt this behaviour. The process of natural
selection tells us a mother who didn’t go back to her home beach was less likely to
have her offspring survive. Maybe there were too many raccoons on the beach she tried,
maybe too many fish near the shore. Maybe it was too rocky to crawl across. The mothers
that stuck with what they knew worked had the most success and this tendency was passed
to her young. It may seem terribly inefficient that a mother
could pass by a perfectly safe beach and travel a thousand miles to go back to her beach,
but, the sea turtle doesn’t know what’s safe and what isn’t. All that’s hardwired
into it’s DNA is to go to its home beach and the offspring have a better chance of
surviving. That’s the great thing about evolution; if an animal has been around for a quarter billion years, it probably knows what it’s doing...
Fascinating! Trying to wrap my head around the 10,000km they travel.