Voices of the Sea Ocean Giants

A giant sperm whale preparing to dive a mile into the abyss.

On its epic dive,

it will hold its breath for longer than this programme lasts.

And it will hunt using the loudest sounds made by any animal on the planet.

CLICKING

Hidden beneath the waves, whales and dolphins lead extraordinary lives.

Travelling the world's oceans, we follow the scientists

who have dedicated their lives to these incredible animals.

They live in a world that's so foreign to us

and give us just a glimpse of their lives.

SQUEAKING

SHE MIMICS DOLPHIN SCREECH

I think we could talk with the dolphins within five years.

Sharing these breathtaking encounters,

two of the world's top underwater cameramen.

It was certainly the biggest whale that I've ever seen.

It just looked enormous underneath me.

Fantastic! Today is the best day of my life.

To survive in this alien world,

whales and dolphins have developed unique powers.

Killer whales use sound as a weapon.

Humpback whales sing their hearts out to the world.

And these strange creatures even see with sound.

They are the voices of the sea.

An estuary in Tasmania, Australia.

Mighty sperm whales lie stranded.

Something's gone wrong with their powers of navigation...

..and the consequences are deadly.

Disorientated and without sufficient water to support its bulk,

this great whale is slowly dying.

Luckily, help is at hand.

His rescuers use their boat to create a wave,

trying to wash him into deeper water.

They carefully cover up his sunburned skin.

And finally they use a net to tow him to safety.

Free at last.

Once clear of the shallows, he starts sending out loud clicks,

using the echoes to form a mental picture of the world around him.

CLICKING

Soon, he is back in the safety of deep water.

But sperm whales don't just use sound to navigate.

Their voices are central to their very existence.

Sperm whales are regular visitors to the very deep waters

of the Caribbean island of Dominica.

Here, scientists are trying to understand how sperm whales

use sound underwater.

It's a source of endless fascination for biologist Shane Gero.

I think I like the sperm whales in particular because they're deep divers.

They live in a world that's so foreign to us

and give us just a glimpse of their lives.

It's almost as if they have this big secret that they're not willing

to share and I just have to dig away and try and figure out what that is.

The team head out into deeper waters, home of the sperm whales.

But finding them won't be easy.

Sperm whales spend most of their time at depth,

only returning to the surface to breathe.

Andrew Armour and his crew

have been following these whales for over a decade.

Today, they are joined by underwater cameramen Didier Noirot and Doug Allan.

-Right, OK.

-Ready?

-Yep.

The trick to finding sperm whales is to use an underwater microphone,

or hydrophone, and catch them doing what they do best - making noise.

Sound travels faster and further in water than in air,

so the team will be able to hear any whales long before they see them.

So what you want to hear is a series of clicks.

The more you hear, the better. If it sounds like popcorn or bacon frying, we're going to have a good day.

I'm afraid the frying pan's empty!

Sperm whales are the largest predators on the planet.

Here's the male. Wow, he's really well marked.

But even they have enemies.

Pilot whales.

They will attack the sperms. They'll eat the babies and we've seen this interaction.

-The pilot whales will attack the sperm whales?

-Yeah!

Confident that pilot whales don't usually attack humans,

Didier is keen to take a closer look.

Close cousins of the killer whale,

pilot whales are only a third of the size of an adult sperm whale.

But they have strength in numbers.

Hunting in packs up to 100-strong,

they too will be listening out for the sounds of sperm whales.

There is a chance that if we keep following these pilots

that we'll end up tracking them as they track the sperms.

At last, the team begin to hear sperm whales.

But these aren't clicks for navigation -

these are clicks for communication, known as codas.

Codas, codas, codas, codas!

CLICKING

Oh, yeah, I can definitely hear the clicking, yeah.

Can you hear them, Shane?

It gets hard to count more than three because after you get...

It might be a click... Oh!

There she blows! There she blows!

There she blows!

This is the chance to get close to the world's largest predator.

Sperm whale families may contain several generations

of daughters with their babies, overseen by a wise old grandmother.

Shane believes that they communicate through a complex array

of coda clicks which vary from family to family.

But they can also put these clicks to far more lethal use.

It's time for the adults to feed.

For the last 15 minutes, the adult whales have been deep breathing

to store as much oxygen as possible in their huge muscles.

Now it's time to dive.

Doug and Didier can only hold a lungful of air,

so their depth limit is around 60 feet.

But with oxygen stored in their muscles, the sperm whales

can go 100 times deeper and stay down for over an hour.

Until recently, no-one knew how sperm whales hunt in the abyss,

but scientists now believe it happens like this.

The reason sperm whales dive so deep

is that there's lots of food down there...

..including giant squid over 30 feet long.

A mile down, there's no light.

The whale must find its prey through echolocation...

..interpreting the echoes of the clicks it makes.

But these are no ordinary clicks.

These hunting clicks are the loudest sounds made by any living thing,

-louder than a thunderclap.

-THUNDERCLAP

CLICKING

Produced in its five-tonne nose, the whale's clicks travel backwards,

then are reflected forwards through a series of oil-filled lenses

which focus them into a narrow sound beam, like a sonic laser.

For the giant squid, there's nowhere to hide.

While the adults are hunting,

their infants are left at the surface,

baby-sat by an auntie or sister.

But even the best baby-sitters

can lose track of their charges at times.

Out of the blue, a baby heads straight for the boat.

Unusually, it's all alone.

It takes refuge between the hulls,

maybe mistaking them for other whales.

As Doug approaches, it calls out with a stream of loud clicks.

CLICKING

It is said that when an adult sperm whale clicks at a diver

it's like being kicked in the chest by a horse.

While this infant's coda clicks may not be as powerful,

they will still carry for more than a mile,

down to where the adults are feeding.

From out of the blue, the baby's mother appears.

Ignoring Doug and Didier,

she gently shepherds her baby back to the family.

-That was great!

-It's so cute!

It was just great! For a first time, it was super!

-We heard a lot of clicks.

-A lot of clicks.

-Calling clicks. A lot of calling clicks.

-Well, he was clicking at me.

-Yeah, he was clicking. He was calling Mum, you know.

The mum came quickly to fetch him.

-She came right up and took him away.

-Yeah, yeah.

Through their remarkable manipulation of sound,

sperm whales are able to communicate,

navigate and even hunt in the pitch-black abyss.

For a whale, there's no tougher place to survive than here...

..in the frozen Arctic Ocean.

It's home to the most bizarre looking of all toothed whales...

..the unicorn of the sea...

..the narwhal.

To reach new fishing grounds, these whales must migrate

huge distances through constantly shifting fields of ice.

Unable to hold their breath for more than 20 minutes,

they must find regular breathing holes in the ice...

..or they risk becoming trapped, starving or drowning.

So how do they find these tiny air holes

dotted across the vast sheets of ice?

Like sperm whales, narwhals can echolocate.

They fire off a series of sonic pulses and use the echoes

to map the world around them.

In this way, they can locate vital breathing holes

from hundreds of feet away.

As winter closes in,

the sea around the narwhals begins to freeze over,

leaving them with fewer and fewer holes in the ice.

Only by using their sophisticated powers of echolocation

can the narwhals find enough air holes to survive.

But at least narwhals can see the fish they're after.

One group of dolphins is not so lucky.

They live in the last place you might expect to find a dolphin...

..3,000 miles inland...

..in the heart of the Brazilian rainforest.

Flowing through it, the mighty Amazon River -

the planet's largest fresh water system.

In some ways, it makes perfect sense for a dolphin to make its home here.

There are more species of fish in the Amazon

than in the whole Atlantic Ocean.

But how can a dolphin catch fish in water

so muddy that it can't see a thing?

500 kilometres we've done, just...

Cameraman Doug and Brazilian scientist Vera da Silva are on their way to investigate.

It's very, very beautiful. I'm looking forward to going down there.

-Will we be travelling everywhere by boat?

-Just rivers and water.

-And lots of dolphins.

-Lots of dolphins.

This is the creature Vera is studying,

perhaps the strangest dolphin of all.

The boto, or Amazon river dolphin.

Doug is having trouble finding any botos.

For a better view, Vera must take Doug to a very special place.

In the wet season, one of the Amazon's tributaries

the Rio Negro, breaks its banks,

and floods an area of jungle the size of France.

This unique water world is known as the flooded forest.

The water is clearer here than in the main river, but it's choked

with branches and leaves and as dark as well-brewed tea.

Finding these strange dolphins hidden in the forest

would be impossible

if it were not for their natural curiosity.

-Come on, botos!

-No, they are there.

-Yeah, they are there.

-Look, look, look.

-Oh, yeah.

Right here. Another one there. They start showing up now.

Having spotted some botos,

Vera uses her hydrophone to listen to their calls.

-Let's see how much noise these guys are doing now.

-Oh, OK.

-Do you want to listen?

-Yes, a little bit. Thank you.

Yeah, now I hear it. Like a series of "trrrrrrrrrr".

-Oh, now...

-SHE SQUEAKS

You can have it.

Oh, yeah, yeah.

The dolphins are very noisy.

But what are these sounds for?

To find out,

Vera and Doug first need to attract the dolphins close to the boat.

So is there a secret to bringing them closer?

Yes, sometimes they will react to the noise or to some fish.

If we give them some fish, they will come quickly.

-See?

-Oh!

-Three at the same time!

The bizarre-looking boto shows off its slender toothy snout...

..and the enormous bulge on its forehead called the melon.

But to find out how it uses them underwater,

Doug will need to dunk himself in the tea.

The botos are using two completely separate sound systems.

The chattering noises are the sound of them talking to each other.

CHATTERING

But they also appear to be scanning Doug with strange clicks and buzzes.

BUZZING AND CLICKING

This is their echolocation in action.

He came up, took the fish and he swam backwards!

I've never seen a dolphin swim backwards before.

The botos lead Doug deeper into their underwater forest...

..where echolocation allows them

to navigate safely through this tangle of submerged vegetation.

The boto's clicks and buzzes are focused into a sound beam

by its bulging forehead melon.

The beam works like a sonic head-torch,

allowing the dolphin to build up a clear picture of its surroundings.

It's as tangled and spiny underwater as it is on the surface.

Those botos are going to need all their manoeuvrability

and all the sonar skills they possess

to operate in this sort of underwater environment.

While all dolphins can echolocate,

botos' clicks have a higher frequency

and better resolution than any other dolphin,

allowing them to distinguish objects as small as a pin.

Even in zero visibility, catching fish is child's play.

These are the weirdest dolphins that I've ever seen.

They're absolutely... They're just fantastic.

The world of botos is a noisy one, full of clicks and buzzes.

But there are times in life when it pays to be silent.

Killer whales.

The ocean's top predator.

From the tropics to the poles,

they use an extensive vocabulary of clicks

to co-ordinate their deadly attacks.

But sometimes, they become ominously quiet.

Each spring, on the Patagonian beaches of South America,

fur seals give birth to their pups.

Three months later,

the naive pups must leave the safety of the colony

and venture into the sea for the first time.

It's the moment the killers have been waiting for.

But hunting seals isn't easy.

Like all marine mammals, seals have excellent hearing.

A single call could betray the hunters' presence.

So they keep radio silence as they close in for the kill.

The young victims never heard them coming.

While seal-hunting killer whales prefer silence,

there are others that use sound as a sophisticated weapon.

Including a remarkable population found off Iceland,

in the north Atlantic Ocean.

On the Westman Islands,

a team of whale scientists is joined by cameraman Didier Noirot.

Large numbers of killer whales have gathered

to hunt the vast shoals of herring that come here to spawn each spring.

But the coordinated and fluid movements of the shoals

make them exceptionally hard to catch.

So how do these huge predators manage to catch the herring,

and in sufficient numbers to make it worthwhile?

Scientist Volker Deecke is an expert in killer whale acoustics.

-Where do you think we'll find a killer whale?

-We've had really good success right in this area...

Recently, Volker has been investigating how killer whales

break through the herring's defences,

and he thinks it is to do with sound.

To prove his theory,

he and Didier need to get right in close to the action.

Having reached the area where the whales were last seen,

Volker deploys his underwater microphones.

A gathering of sea birds means the herring shoals

must be close to the surface.

Something must have spooked them.

Oh!

Seven or eight together at the top of the waves.

Killer whales.

Volker is perfectly positioned to record

the sounds of the hunting whales.

Three, four.

Be great to see what the whales are doing underwater

-when they're making all these sounds.

-Sure.

To capture the video evidence, Didier uses a pole camera.

You are the ears, I'm the eye.

Getting in the water with feeding killer whales

would be too dangerous in this poor visibility.

Volker gathers his evidence.

WHALES CALL ON TAPE

Yeah, that's the call.

That was a killer whale, no doubt about it, yeah.

After two hours of intensive feeding,

the killers have fallen silent.

The attack is over.

Back at HQ,

the team analyse the killers' calls

and reveal the whales' secret weapon.

What you'll hear is a lot of echolocation clicks,

but then you'll hear something special. Here we go.

HUMMING AND CLICKING

Whistles, echolocation.

CLICKING

And now have a good listen.

HIGHPITCHED WHISTLE

This high-pitched note is what's known as the herding call.

The idea is that the whales may be using the sound

to essentially cause resonance in the herring's swim bladder.

That makes the herring's guts vibrate

and that makes the herring very uncomfortable.

Panicked by the gut-wrenching noise,

the herring bunch so tightly together,

they have no room for manoeuvre.

They school together, then bang!

The killer whales then deliver devastating tail-swipes

with the force of an exploding grenade.

Job done, the whales can relax over a leisurely feast of stunned fish.

Whales and dolphins use their voices to keep the family group together

but there are times when talking just isn't enough.

In the rich waters off New Zealand,

hundreds of dolphins travel together in super-pods.

Moving in such large groups requires clear communication.

But clicks and whistles only have a limited range.

The only way to broadcast messages across the group

is by generating louder, more explosive sounds.

Different body smacks convey different meanings.

It's thought dolphins may use such acrobatic leaps

to signal the discovery of large shoals of fish.

Body percussion is a key ingredient in dolphin communication,

and they will use it even to signal to us.

On Brazil's Atlantic coast,

one remarkable group of dolphins is in cahoots with the locals.

Fishermen from the town of Laguna have discovered they do better

when they don't fish alone.

Each dawn, they gather in the murky shallows of the estuary

and wait for help to arrive.

Their fishing partners are a group of bottlenose dolphins.

Scientist Arnaldo Russo claims that this local dolphin pod

have learned to communicate with us.

The fishermen know when they can throw their nets

because the dolphin's making special signs.

But what are these special signs

that the dolphins give the fishermen?

They can give a head-slap or a tail-slap into the water.

-When the fishermen see those special signs, they throw their nets.

-Yeah.

It's like a conversation.

A conversation that starts with the dolphins letting the fishermen know

where the mullet are by slapping the water loudly with their tails.

Go, go, go.

The dolphins do the hard work herding the mullet.

The fish are handed to the fisherman on a plate.

But what the dolphins stand to gain is less obvious.

Since they detect prey by echolocation,

they have no problem finding fish in the murky water.

But catching them is difficult.

By casting their nets, the fishermen scatter the shoal,

making it easier for the dolphins to snap up individual fish.

This culture of co-operation

has been going on at Laguna for over a century.

Dolphin mothers teach their calves how to slap the water

to signal to the fishermen.

And the fishermen teach their sons to recognise the dolphins' signals.

I've never seen this anywhere else in the world.

-No, it's beautiful. It's amazing.

-It is.

But is there more that creatures like these are trying to communicate

that we are simply missing?

One enduring mystery

surrounds the most celebrated musical event in nature...

..the songs of the humpback whale,

currently playing off the islands of Hawaii,

in the middle of the Pacific Ocean.

Before the singing can begin,

the performers must give a master-class in percussion.

40-tonne bodies hit the sea with an ear-splitting crash.

And giant tail flukes thunder out a message to rival males.

Didier makes sure to get a front row seat.

Neutral!

The ocean reverberates with explosions of bubbles.

And then the opera begins.

WHALE SONG

The song of the humpback, it's something really beautiful.

The most beautiful sound you can hear in the sea.

You're the scientist.

Jim Darling has spent the last 30 years trying to work out

the meaning of these extraordinary songs.

WHALE SONG

Wow!

-There are a few of them, huh?

-Yeah, there's a few.

-There's one close and three or four in the background.

-OK.

Yeah, they are a beautiful sound.

WHALE SONG

With his mouth shut tight, shunting air back and forth through a larynx

the size of a phone-box -

technically, he's humming, not singing.

Whatever it is, it's a voice that can travel thousands of miles

across entire oceans.

The male's recital may include half a dozen distinct themes

which he's learned from other males.

He may even add his own improvised variations.

By copying sequences from each other,

males constantly evolve their repertoire.

But does it have a purpose?

For a long time, it was presumed that the singers were singing

to attract a female.

And I think people like that idea,

because it's been written about a lot.

But there's not a shred of evidence for it.

We've never seen a female approach a male.

If they aren't calling a mate, then why are they singing?

Is it a way for males to size each other up?

Could they even be making music for pleasure?

The truth is that nobody knows.

The enigmatic voices of whales and dolphins

have captured our imagination for centuries.

Scientists may one day find out the whole truth

behind these extraordinary voices of the sea,

but, for now, the private life of these ocean giants

remains wonderfully mysterious.