Hi! Today I am joined by Virginia Schutte and we are going to be talking about how animals
navigate through the open ocean. Navigation on land is quite easy because you can use
visual cues such as the sun, the moon and the stars or even landmarks. Certain insects
also use optic flow, which allows them to translate the change of visual patterns into
the movements they have carried out over an area. However, this all changes underwater.
So imagine you're a sea turtle trying to swim across an entire ocean - the light fades quickly
as you dive down deeper and the whole ocean pretty much looks the same, all the time.
So how do you get from Point A to Point B?
[INTRO designed by Caro Waro & Cristina de Manuel]
In spite of its visual difficulties the ocean provides navigational possibilities that the
land doesn't. For instance, wind direction also determines wave direction, which can
be felt underwater, and pressure can also provide information on depth.
There are three main ways that animals navigate long distances through the ocean. The first
is geomagnetic. So animals can use the Earth's magnetic field both to keep track of where
they are and which direction they're going. This sounds like a really fancy superpower,
but even invertebrates like lobster can keep track of their location this way.
Ocean animals also use chemical cues to get around, especially in the earlier stages of
their lives. Many larvae actually float close to the surface of the ocean going wherever
the currents take them. They know that it's time to remove themselves from the currents
and swim to the bottom when they sense the chemical signature of the home they're looking
for, such as a coral reef. Depending on the situation, these larvae can detect chemical
signatures at distances on the order of 100s of kilometres. That's like being in London
and sniffing your way home to Oxford.
The third tool that marine animals use for navigation is the way the water moves around
them, or hydrodynamics. Baby sea turtles are famous for making their way as quickly as
possible to the water once they hatch from their eggs on the beach, because otherwise
they might get eaten. But once they hit the waves, they have to keep swimming out to sea
to stay safe. If you've ever played in the waves and fallen down you know how disorienting
it can be with all that violent water movement all around you, but this provides information
to the sea turtles on which way they're facing. The water moves their bodies in different
ways, depending on whether they're facing out to the ocean, or back towards the beach.
One of the features of long distance navigation is that many animals use all or switch between
different methods and it can sometimes be a bit hard to know which one they're doing.
For instance, we know that baby sea turtles first of all use these hydrodynamics to figure
out how to get out to the open ocean, and they stay there until they need to breed and
find a new home to lay eggs. Then, they use the Earth's magnetic field as a map to tell
them where they are and as a compass to tell them which way to go.
Virginia: Once they get close to the beach where they were born they might switch to
using chemical cues to guide them to the exact spot where they want to be.
Researchers think that these three navigational methods explain how most if not all marine
animals navigate through the sea. However, it is quite hard to confirm exactly which
method an animal is using at each point in time.
For example, great white sharks regularly move between California and Hawaii in the
Pacific. Now these animals are really important for keeping the ocean's food chains in balance,
but their numbers are declining world wide. If we knew how they navigated between those
two states we might be able to protect them better but how do you study a great white
shark in the lab?
The same is true for the long distance record holder which was a gray whale tagged in Russia,
which was found to go from the Arctic to Alaska, go down to the tip of Mexico and then return
to Russia. This migration was a total of 22500km, just over half of the Earth's circumference
at the Equator. But how can you humanely determine how a whale navigates?
There's plenty that we don't know, and a lot that we may never know, about how marine animals
navigate long distances through the oceans, but one thing is clear, these animals are
uniquely prepared to tackle this challenge.
We hope you enjoyed this! Thank you so much to Virginia Schutte for scripting this episode
and making it happen! She is a marine biologist expert and she also runs her own blog over
at Real Life Science, and she is a science media consultant - so feel free to go check
out her stuff over there! And as always, thank you so much for watching us, and I'll see
you in the next one! Bye!
[ART & ANIMATION - Caro Waro & Cristina de Manuel]
[MUSIC: Thastor & CryoSleepKitten] [Hosting: Virginia Schutte and Inés Dawson]
[Scripting: Virginia Schutte] [Editing: Inés Dawson]