The Pacific.
The largest, deepest ocean on the planet.
And an alien, acoustic world
where animals use sound in otherworldly ways.
None more so than the ocean's greatest singers.
Humpback whales.
Each year, over 10,000 humpbacks gather off the coasts of Hawaii
to win the chance to breed.
And to join together with nature's most complex and intriguing song.
Using the latest underwater microphones,
we can now immerse ourselves in their aquatic symphony like never before.
Eighty feet below the surface...
this male has been singing for over 20 minutes on a single breath.
He's showing off in the underwater equivalent of a singing contest.
His song is a complex combination of distinctive phrases
and captivating sounds...
that carry out into the blue.
Other males are listening in.
And if they like what they hear, they copy it...
precisely.
Adding it to their own song.
Amazingly, the males mimic each other so often,
they eventually all end up singing the same song.
A unique tune for that season.
The exact meaning of their song remains a mystery.
But it's clear, like for us, singing brings humpbacks together.
But there are other, more subtle whale calls here.
This new mother arrived two months ago to give birth in Hawaii's warm waters.
Her calf is still vulnerable,
and the pair keep in contact with a quiet chatter of chirps and grunts.
Their own secret language.
Even with her calf in tow,
she's attracting the attention of the males.
And that can be a risky business.
Brought together through their singing, the males' talent show is hotting up.
They've spotted the mother...
and begin charging as a group, each vying to impress her.
Known as a heat run...
this is the biggest courtship battle in nature.
Each challenger tries to out-maneuver the others...
bellowing out calls that carry for miles.
In the melee, the mother and calf risk being split up.
A chase can last for three hours...
until a clear winner rises to the top.
Through his song and displays of strength,
this male has won the right to escort and court the mother...
as they begin their epic migration to their feeding grounds across the ocean.
From Hawaii, the Pacific stretches for thousands of miles.
It covers a third of the planet,
dropping in places to five times the depth of the Grand Canyon.
It's home to more species than any other ocean.
Sound travels five times further and faster underwater than in air.
So, it's sound, not sight...
that most creatures here rely on.
The most widespread sound of the oceans is not whale song, but this.
A near-constant crackle of pops and clicks that fills the sea.
It comes from a remarkable source...
produced by millions of tiny creatures
that possess astonishing acoustic superpowers.
This industrious little shrimp is busy excavating his home.
His oversized pincers are ideal for shoveling coral sand.
But they also hold the sonic secret to how he defends his burrow.
With such a sought-after location, he needs to be wary.
Because another shrimp has his eye on a new home.
As the interloper closes in...
the neighbors know it's time to take cover.
Because these are pistol shrimp,
and each is packing a sonic stun gun.
Using the latest underwater microphones,
we can now listen to their acoustic battles like never before.
His specialist claw locks like a rifle...
and releases.
By slowing down sound 500 times,
we can hear what is actually happening.
The shrimp's claw snaps with such incredible speed...
it superheats the water to over 8000 degrees Fahrenheit...
creating a high-pressure bubble.
And the bubble collapsing produces a bang so loud
it pulses shock waves through the water.
Sending the intruder packing.
Relative to its size,
the pistol shrimp makes the loudest sound in the sea.
And the clicks and pops of so many mini battles
from across the ocean floor mix with the noise of the sea
to create the signature sound of the Pacific.
Whilst some ocean dwellers battle with sound...
others use it in far more harmonious ways.
Off the Pacific Coast of Costa Rica,
one group of animals has a surprising acoustic trick
to find one another in the open ocean.
Dolphins.
This family, 60 strong, are heading offshore
to meet other pods and search for food.
From the surface, their voices can hardly be heard.
But beneath the waves, it's a different story.
Within the family, they communicate using a complex language
of high-pitched whistles and rapid-fire clicks.
This lets them keep in touch on the move.
But to send out a message to other pods,
these dolphins have learned to take sound to another level.
These are spinner dolphins.
The only dolphins in the world to leap like this.
Their acrobatics look like a visual display.
But it's actually about sound.
They're using the surface of the ocean like a drum.
Their spinning leap creates a boom...
that travels through the water at a mile per second.
It's an invitation to other spinner pods nearby
to come together.
There's also a secret signal in the trail of bubbles they leave behind.
Remarkably, these microbubbles left after each impact
hang in the water for up to five hours.
By following these intricately laid bubble trails
through the empty open ocean,
other pods from miles around join the family.
As the numbers swell, a super pod begins to form.
A thousand strong...
and up to half a mile wide.
Together, dolphin families can hunt greater swathes of ocean
and now use sound to socialize between the different groups.
Incredibly, this is only a fraction of their chatter.
Half their calls are above our hearing range.
But we can now tune in to the dolphins' secret conversation...
and hear how they constantly talk to one another
to keep the super pod together.
Gatherings like this are one of the Pacific's greatest spectacles.
And it's all down to the spinner dolphin's mastery of sound.
But to discover the most bizarre ways animals communicate
through the vastness of the open ocean...
we need to descend into a deep, hidden world.
In the darkness, tiny creatures called plankton...
some microscopic in size...
make minuscule sounds as they travel through the water.
In their billions, they create the buzz of the deep ocean.
Diving further, the creatures get even stranger.
And so do the sounds.
At half a mile down,
deepwater listening stations pick up otherworldly chatter.
At specific depths,
the water density means sound can travel further
than anywhere else on the planet.
This blue whale song...
could be coming from a whale a thousand miles away.
It's the furthest-reaching call in the natural world
and is how the largest creatures on Earth keep in touch across oceans...
without ever seeing each other.
But the most ingenious use of sound in all the world's oceans occurs
off the Pacific Coast of Alaska.
Each spring, these shores erupt with life.
From the depths,
a spring bloom of plankton turns the water emerald green
and draws up millions of herring...
bringing in hungry predators from far and wide.
After a 5,000-mile migration from Hawaii,
the humpbacks have arrived at their feeding grounds.
They haven't eaten for up to five months,
and they're famished.
On the surface, they snack on tiny morsels of krill and plankton.
And that's not nearly enough for a hungry humpback.
They're after the vast schools of herring hiding beneath.
And to catch them,
they'll have to set nature's most elaborate acoustic trap.
They fan out in formation...
and then dive in synchrony.
Now, onboard microphones and cameras allow us to ride into the depths
with the hunting party
to reveal the humpbacks' feeding behavior in an extraordinary new way.
Keeping in touch with low grunts...
they swim down beneath the herring shoal.
Then the lead whale does something remarkable.
From his blowhole, he creates a stream of bubbles.
He can keep blowing for over a minute.
As the bubbles rise,
they create a curtain surrounding the fish, a bubble net.
At the same time, the leader reveals his secret acoustic weapon:
a haunting war cry.
This eerie call bounces off the rising bubble curtain
and scares the herring into the center of the net.
The leader now blasts out its final call
telling the hunting party to head to the surface...
so the feast can begin.
Using this bubble netting technique,
each whale can devour over a ton of herring a day.
This unique view into the whale's world sheds new light
on the extraordinary way that humpbacks harness the power of sound.
To gain new insights into the sonic world of humpback whales...
the Earthsounds team followed them from their breeding grounds in Hawaii...
to their feeding grounds in the North Pacific.
Fish are jumping.
Yeah.
Nice.
Here, they teamed up with researchers
from the University of Alaska and the Alaska Whale Foundation
who are using pioneering new technology to study bubble net feeding.
Despite 23 years of watching these whales, we still know so little about them
because we just didn't have the technology that would give us any insight
or give us that window into what they're doing
until we start getting tags like this.
Each tag contains a camera,
microphone, and movement sensors
that allows the team to track the whales underwater.
They attach temporarily with a series of small suction cups
that cause no harm to the whale's thick skin
and are deployed from the end of a 10-foot-long pole.
- I see a fluke. - Cool.
Alaska's humpbacks are considered endangered.
So using the tags requires special permits and a very careful approach.
You're slowly trying to get into the group,
be a part of the herd.
It's a really passive way that we're doing this.
Just the slight change of speed can change their behavior,
and you don't want that.
Amazingly,
fewer than 30 whales are known to sing this special feeding call.
They're known as vocalizers.
But it's still unproven whether the same whale also blows the bubble ring.
Andy has spotted one of these whales, called Arpeggio,
who might give them the answer.
Arpeggio has been in the sighting database since the '90s
and believed to be one of the key vocalizers in the group.
So, I mean, getting a tag on that whale was pretty exciting.
But placing a tag on the right whale at just the right spot...
Still there?
...is easier said than done.
Seem to just be knowing
- to stay just far enough away. - Yeah.
With a careful and patient approach,
the whales continue to bubble net feed close by.
Bubbles in front of us.
- How close? - Like, going under us.
Oh, yeah.
- Yes. - Yeah.
Okay, right here.
There it is. Right in front of us.
Right in front of us.
With the whales back on the surface,
the team has the briefest moment to carefully deploy the tag.
Nice!
Nice, Maddy. You're just like a boss.
Yeah!
With multiple tags applied amongst the group...
it was now over to the whales to take the tags into their world.
I hear a beep.
While the team track them from a distance
and one whale is in the midst of the action.
- There we go. - Are you sure?
Arpeggio.
Oh, yes, it's Arpeggio. That's Arpeggio.
Awesome.
The tags can stay on for up to 24 hours before detaching.
And once recovered and downloaded,
the team is given the incredible new glimpse
into the whale's world they've been waiting for.
Here we go.
Right from the start.
That's awesome.
So this is Arpeggio.
Listen to that.
That's crazy.
You can hear the feeding call.
And the data from Arpeggio's tag reveals
how the same whale can produce the bubble ring and sing the feeding call.
Now that we know it's on a vocalizer, we have a much better idea
as to how the animals are using these vocalizations to corral the herring.
We've never had any ability to see underwater like this
and to track that vocalizer until now.
The analysis the team is doing of the tag data
will change the way we look at the hunting skill
of the Pacific's greatest singers.