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The Pacific.

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The largest, deepest ocean on the planet.

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{\an8}And an alien, acoustic world

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where animals use sound
in otherworldly ways.

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None more so
than the ocean's greatest singers.

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Humpback whales.

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Each year, over 10,000 humpbacks
gather off the coasts of Hawaii

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to win the chance to breed.

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And to join together with
nature's most complex and intriguing song.

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Using the latest underwater microphones,

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we can now immerse ourselves in
their aquatic symphony like never before.

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Eighty feet below the surface...

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this male has been singing
for over 20 minutes on a single breath.

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He's showing off in the underwater
equivalent of a singing contest.

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His song is a complex combination
of distinctive phrases

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and captivating sounds...

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that carry out into the blue.

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Other males are listening in.

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And if they like what they hear,
they copy it...

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precisely.

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Adding it to their own song.

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Amazingly,
the males mimic each other so often,

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they eventually all end up
singing the same song.

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A unique tune for that season.

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The exact meaning of their song
remains a mystery.

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But it's clear, like for us,
singing brings humpbacks together.

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But there are other,
more subtle whale calls here.

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This new mother arrived two months ago
to give birth in Hawaii's warm waters.

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Her calf is still vulnerable,

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and the pair keep in contact
with a quiet chatter of chirps and grunts.

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Their own secret language.

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Even with her calf in tow,

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she's attracting
the attention of the males.

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And that can be a risky business.

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Brought together through their singing,
the males' talent show is hotting up.

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They've spotted the mother...

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and begin charging as a group,
each vying to impress her.

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Known as a heat run...

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this is the biggest courtship battle
in nature.

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Each challenger
tries to out-maneuver the others...

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bellowing out calls that carry for miles.

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In the melee,
the mother and calf risk being split up.

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A chase can last for three hours...

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until a clear winner rises to the top.

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Through his song and displays of strength,

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this male has won the right
to escort and court the mother...

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as they begin their epic migration
to their feeding grounds across the ocean.

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From Hawaii, the Pacific stretches
for thousands of miles.

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It covers a third of the planet,

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dropping in places to five times the depth
of the Grand Canyon.

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It's home to more species
than any other ocean.

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Sound travels five times further
and faster underwater than in air.

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So, it's sound, not sight...

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that most creatures here rely on.

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The most widespread sound of the oceans
is not whale song, but this.

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A near-constant crackle of pops and clicks
that fills the sea.

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It comes from a remarkable source...

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produced by millions of tiny creatures

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that possess
astonishing acoustic superpowers.

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This industrious little shrimp
is busy excavating his home.

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His oversized pincers
are ideal for shoveling coral sand.

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But they also hold the sonic secret
to how he defends his burrow.

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With such a sought-after location,
he needs to be wary.

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Because another shrimp
has his eye on a new home.

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As the interloper closes in...

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the neighbors know
it's time to take cover.

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Because these are pistol shrimp,

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and each is packing a sonic stun gun.

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Using the latest underwater microphones,

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we can now listen to
their acoustic battles like never before.

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His specialist claw locks like a rifle...

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and releases.

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By slowing down sound 500 times,

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we can hear what is actually happening.

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The shrimp's claw snaps
with such incredible speed...

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it superheats the water
to over 8000 degrees Fahrenheit...

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creating a high-pressure bubble.

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And the bubble collapsing
produces a bang so loud

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it pulses shock waves through the water.

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Sending the intruder packing.

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Relative to its size,

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the pistol shrimp
makes the loudest sound in the sea.

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And the clicks and pops
of so many mini battles

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from across the ocean floor
mix with the noise of the sea

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to create
the signature sound of the Pacific.

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Whilst some ocean dwellers
battle with sound...

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others use it in far more harmonious ways.

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Off the Pacific Coast of Costa Rica,

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one group of animals has
a surprising acoustic trick

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to find one another in the open ocean.

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Dolphins.

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This family, 60 strong,
are heading offshore

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to meet other pods and search for food.

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From the surface,
their voices can hardly be heard.

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But beneath the waves,
it's a different story.

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Within the family,
they communicate using a complex language

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of high-pitched whistles
and rapid-fire clicks.

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This lets them keep in touch on the move.

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But to send out a message to other pods,

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these dolphins have learned
to take sound to another level.

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These are spinner dolphins.

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The only dolphins in the world
to leap like this.

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Their acrobatics
look like a visual display.

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But it's actually about sound.

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They're using the surface of the ocean
like a drum.

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Their spinning leap creates a boom...

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that travels through the water
at a mile per second.

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It's an invitation
to other spinner pods nearby

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to come together.

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There's also a secret signal
in the trail of bubbles they leave behind.

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Remarkably, these microbubbles
left after each impact

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hang in the water for up to five hours.

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By following
these intricately laid bubble trails

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through the empty open ocean,

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other pods from miles around
join the family.

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As the numbers swell,
a super pod begins to form.

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A thousand strong...

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and up to half a mile wide.

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Together, dolphin families can hunt
greater swathes of ocean

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and now use sound
to socialize between the different groups.

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Incredibly,
this is only a fraction of their chatter.

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Half their calls are
above our hearing range.

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But we can now tune in
to the dolphins' secret conversation...

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and hear
how they constantly talk to one another

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to keep the super pod together.

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Gatherings like this are
one of the Pacific's greatest spectacles.

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And it's all down to
the spinner dolphin's mastery of sound.

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But to discover
the most bizarre ways animals communicate

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through the vastness of the open ocean...

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we need to descend
into a deep, hidden world.

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In the darkness,
tiny creatures called plankton...

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some microscopic in size...

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make minuscule sounds
as they travel through the water.

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In their billions,
they create the buzz of the deep ocean.

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Diving further,
the creatures get even stranger.

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And so do the sounds.

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At half a mile down,

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deepwater listening stations
pick up otherworldly chatter.

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At specific depths,

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the water density means
sound can travel further

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than anywhere else on the planet.

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This blue whale song...

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could be coming from
a whale a thousand miles away.

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It's the furthest-reaching call
in the natural world

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and is how the largest creatures on Earth
keep in touch across oceans...

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without ever seeing each other.

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But the most ingenious use of sound
in all the world's oceans occurs

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off the Pacific Coast of Alaska.

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Each spring, these shores erupt with life.

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From the depths,

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a spring bloom of plankton
turns the water emerald green

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and draws up millions of herring...

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bringing in hungry predators
from far and wide.

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After a 5,000-mile migration from Hawaii,

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the humpbacks have arrived
at their feeding grounds.

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They haven't eaten for up to five months,

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and they're famished.

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On the surface, they snack
on tiny morsels of krill and plankton.

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And that's not nearly enough
for a hungry humpback.

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They're after the vast schools of herring
hiding beneath.

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And to catch them,

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they'll have to set
nature's most elaborate acoustic trap.

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They fan out in formation...

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and then dive in synchrony.

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Now, onboard microphones and cameras
allow us to ride into the depths

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with the hunting party

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to reveal the humpbacks' feeding behavior
in an extraordinary new way.

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Keeping in touch with low grunts...

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they swim down beneath the herring shoal.

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Then the lead whale
does something remarkable.

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From his blowhole,
he creates a stream of bubbles.

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He can keep blowing for over a minute.

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As the bubbles rise,

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they create a curtain
surrounding the fish, a bubble net.

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At the same time, the leader reveals
his secret acoustic weapon:

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a haunting war cry.

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This eerie call bounces
off the rising bubble curtain

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and scares the herring
into the center of the net.

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The leader now blasts out its final call

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telling the hunting party
to head to the surface...

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so the feast can begin.

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Using this bubble netting technique,

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each whale can devour
over a ton of herring a day.

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This unique view into the whale's world
sheds new light

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on the extraordinary way
that humpbacks harness the power of sound.

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To gain new insights
into the sonic world of humpback whales...

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the <i>Earthsounds</i> team followed them
from their breeding grounds in Hawaii...

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to their feeding grounds
in the North Pacific.

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Fish are jumping.

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Yeah.

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Nice.

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Here, they teamed up with researchers

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from the University of Alaska
and the Alaska Whale Foundation

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who are using pioneering new technology
to study bubble net feeding.

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{\an8}Despite 23 years of watching these whales,
we still know so little about them

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{\an8}because we just didn't have the
technology that would give us any insight

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{\an8}or give us that window
into what they're doing

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until we start getting tags like this.

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00:28:18,490 --> 00:28:20,909
Each tag contains a camera,

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00:28:20,909 --> 00:28:23,120
microphone, and movement sensors

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00:28:23,787 --> 00:28:26,790
that allows the team
to track the whales underwater.

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They attach temporarily
with a series of small suction cups

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that cause no harm
to the whale's thick skin

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and are deployed
from the end of a 10-foot-long pole.

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00:28:43,473 --> 00:28:45,350
- I see a fluke.
- Cool.

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00:28:47,436 --> 00:28:50,439
Alaska's humpbacks
are considered endangered.

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00:28:51,064 --> 00:28:57,404
So using the tags requires special permits
and a very careful approach.

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You're slowly trying
to get into the group,

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be a part of the herd.

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00:29:07,748 --> 00:29:10,959
It's a really passive way
that we're doing this.

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Just the slight change of speed
can change their behavior,

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and you don't want that.

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Amazingly,

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fewer than 30 whales are
known to sing this special feeding call.

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They're known as vocalizers.

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00:29:28,477 --> 00:29:33,106
But it's still unproven whether
the same whale also blows the bubble ring.

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00:29:34,608 --> 00:29:38,654
Andy has spotted one of these whales,
called Arpeggio,

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who might give them the answer.

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Arpeggio has been
in the sighting database since the '90s

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and believed to be
one of the key vocalizers in the group.

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So, I mean, getting a tag on that whale
was pretty exciting.

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But placing a tag on
the right whale at just the right spot...

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Still there?

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...is easier said than done.

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Seem to just be knowing

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- to stay just far enough away.
- Yeah.

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With a careful and patient approach,

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the whales continue to bubble net feed
close by.

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Bubbles in front of us.

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- How close?
- Like, going under us.

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00:30:32,875 --> 00:30:35,711
Oh, yeah.

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00:30:40,757 --> 00:30:42,176
- Yes.
- Yeah.

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00:30:42,176 --> 00:30:43,760
Okay, right here.

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There it is. Right in front of us.

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Right in front of us.

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With the whales back on the surface,

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the team has the briefest moment
to carefully deploy the tag.

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00:31:06,617 --> 00:31:07,951
Nice!

239
00:31:09,119 --> 00:31:11,747
Nice, Maddy. You're just like a boss.

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00:31:19,379 --> 00:31:20,380
Yeah!

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With multiple tags applied
amongst the group...

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it was now over to the whales
to take the tags into their world.

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I hear a beep.

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While the team track them from a distance

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00:31:43,862 --> 00:31:46,448
and one whale is
in the midst of the action.

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00:31:46,448 --> 00:31:48,450
- There we go.
- Are you sure?

247
00:31:48,450 --> 00:31:49,535
Arpeggio.

248
00:31:49,535 --> 00:31:52,037
Oh, yes, it's Arpeggio. That's Arpeggio.

249
00:31:53,038 --> 00:31:54,039
Awesome.

250
00:31:55,165 --> 00:31:59,503
The tags can stay on
for up to 24 hours before detaching.

251
00:32:02,381 --> 00:32:04,633
And once recovered and downloaded,

252
00:32:05,884 --> 00:32:08,762
the team is given
the incredible new glimpse

253
00:32:08,762 --> 00:32:12,015
into the whale's world
they've been waiting for.

254
00:32:12,015 --> 00:32:13,100
Here we go.

255
00:32:15,477 --> 00:32:17,604
Right from the start.

256
00:32:20,732 --> 00:32:22,359
That's awesome.

257
00:32:26,363 --> 00:32:29,783
So this is Arpeggio.

258
00:32:31,743 --> 00:32:32,744
Listen to that.

259
00:32:33,620 --> 00:32:34,955
That's crazy.

260
00:32:39,126 --> 00:32:40,794
You can hear the feeding call.

261
00:32:42,004 --> 00:32:45,424
And the data from Arpeggio's tag reveals

262
00:32:45,424 --> 00:32:51,471
how the same whale can produce
the bubble ring and sing the feeding call.

263
00:32:53,307 --> 00:32:56,518
Now that we know it's on
a vocalizer, we have a much better idea

264
00:32:56,518 --> 00:33:00,564
as to how the animals are using
these vocalizations to corral the herring.

265
00:33:01,982 --> 00:33:05,944
We've never had any ability
to see underwater like this

266
00:33:05,944 --> 00:33:08,572
and to track that vocalizer until now.

267
00:33:13,744 --> 00:33:16,997
The analysis the team is doing
of the tag data

268
00:33:17,956 --> 00:33:22,252
will change
the way we look at the hunting skill

269
00:33:22,252 --> 00:33:25,380
of the Pacific's greatest singers.