Original subtitles

WAVES CRASH

WAVES ROAR

Our ocean has seasons, just as the land does.

The most turbulent of them is winter.

Storms at sea whip up immense waves.

They may travel for thousands of miles

before they make landfall.

Influenced by the seasons...

...these seas

are in constant turmoil...

...so the animals here

have to be among

the most adaptable on Earth.

The Pacific coast of South America.

Sea lions have lived on

this exposed shore for generations,

but extreme storms

are now more common.

Mothers and pups remain at the colony...

...but a few young males

choose to take a risk.

SEA LIONS BARK

They leave the coast

and search for food

in unfamiliar waters.

BIRDS CALL

SEA LION BLOWS

The most intrepid males even venture

where few marine animals ever go.

Upriver.

30 miles from the ocean...

SEA LION SNIFFS

...this is an alien world.

SEA LION SNUFFLES

In these tranquil waters...

...there are fish.

But hungry sea lions

need at least 8kg of food a day.

Something substantial

catches the eye of this male.

Black-necked swans.

Unlikely prey for a sea lion.

SEA LION BARKS

SWANS CALL

SWANS SCREECH

A little too enthusiastic.

The swans know this wetland

far better than he does.

They take cover in a flooded forest.

With so many obstacles,

he has little chance of getting near them.

He must be patient.

Finally, the swans venture

into open water.

He's careful not to break the surface.

SWANS CALL

SWANS SCREECH

CHIRPING

A prize far greater than a fish.

Such bold hunting behaviour

has only been witnessed in recent years.

It's just one way in which sea lions

are adapting to increasingly

hostile winters out at sea.

While some choose to escape the stormy coast...

...others seem undeterred.

For many months, this southern right whale

has travelled alone,

across the world's roughest seas.

All to reach one special place.

The sheltered bay in Patagonia

where it's likely she was born.

She is here to breed.

Something she only does

every four years.

First, she must perfect her mating call.

DEEP CALL

A seductive song.

MOANS ECHO

It's thought that she deliberately selects

parts of the seabed

which amplify the sound.

But will anyone answer?

The males have arrived.

Her serenade is causing quite the stir.

Females assess the males

by the size of their splashes.

Impressive!

SOFT GRUNTING

Now the males are allowed to approach.

Whales have poor eyesight,

but surprisingly sensitive skin,

so the female rolls over

for a gentle belly rub.

HEAVY THUD

But in their eagerness,

some males are rather clumsy.

Others are a little too brazen.

One extends his three-metre-long penis in her direction.

But courtship can't be rushed.

For up to two days,

she rejects the males...

...one...

...after the other...

...until only the most devoted suitor

remains beside her.

There is one last test.

Hours of tender caressing.

She finally accepts him.

Every pairing is valuable

because last century,

these whales were hunted

to near extinction.

But the whaling ban increased their population

from just 300 to around 25,000...

...with one surprising twist.

Their colour.

One of the few surviving mothers

happened to carry a rare gene

for white skin, which spread

as their numbers multiplied.

Now one in every 20 calves

is born white.

A symbol of hope in this bay every winter.

Between the freezing Poles and the warm Tropics

lie areas called

the temperate zones.

One is in the northern hemisphere.

Another lies in the south.

The seas within these temperate zones are seasonal

and are in constant flux throughout the year.

In winter, storms churn the waters,

and that raises nutrients from the deep.

As spring approaches,

the increase in nutrients and light

enables tiny drifting plants

and animals to multiply.

This abundance of plankton

is food for a very peculiar crustacean.

A porcelain crab...

...which collects plankton from the current

using specialised fans.

But he does need space...

...in which to deploy them.

And in this bay in Chile,

that is at a premium.

More than 200 million have joined him for the banquet.

It's one of the largest aggregations

of crabs ever recorded.

Over 1,000 crabs

are stacked in every square metre.

They can't get a foothold to feed.

Time to find some room.

By flapping their abdomens,

they propel themselves -

not just upside down, but backwards too.

Finally, a quieter spot.

But it's like trying to dine

on a roller-coaster.

As the current strengthens,

so does the flow of plankton...

...triggering behaviour

that has never been filmed before.

The crabs organise themselves

into lines.

How hundreds of millions co-ordinate their actions

is not known...

...but by creating channels,

the plankton is swept between them.

A food superhighway,

with room on all sides to feast.

This remarkable behaviour

enables everyone to get their fill.

Dinner, at last.

The plankton bloom feeds more than crabs.

It transforms these seas into the most fertile on Earth...

...fuelling an explosion

of marine life.

This signals the arrival of spring.

Across the planet,

the sunlight triggers a great greening.

Just as forests flourish on land...

BIRDSONG

...so they do in the water.

Vast canopies of kelp.

It's one of the fastest-growing organisms on Earth,

and in spring, can lengthen by

half a metre every day.

These sub-marine jungles have a combined area

larger than the Amazon rainforest.

The greatest variety of kelp

is found round the islands of Japan.

These lush fronds

conceal a rarely-seen fish.

A shy little eelpout.

Just 10cm long.

This young female is searching the vast forest

for her first-ever mate.

But the forest is eerily quiet.

Only a predatory rockfish lingers here.

In the open,

bold breeding colours

make her only too conspicuous.

A narrow escape.

This is more like it.

A rock full of holes,

where eelpouts like to hide.

Perhaps there is a mate here.

A male!

He's perfect.

But he's already taken.

There are other males...

...but they all have partners.

She's arrived too late.

Now her only chance to win a mate

is to challenge another female...

...in mouth-to-mouth combat.

Jaw wrestling tests strength.

As her mouth is smaller,

she is at a serious disadvantage.

The duel draws them out into the open.

This alerts the rockfish.

Her opponent's bigger mouth

has her pinned.

As she backs away,

she spots an opportunity.

The male is now unguarded.

This is her chance.

Her rival returns to reclaim him...

...but she isn't watching her back.

With a little help,

she has succeeded.

Perhaps next year,

she will arrive on time.

Stretching from the edge of Siberia

to the tropical Pacific,

the islands of Japan are seasonally extreme.

And when spring gives way to summer,

temperatures at the coast

can rise by 50 degrees Celsius

in a matter of weeks.

A particular challenge for those that live here...

...including an unusual creature

that makes its home in tidal rock pools.

An octopus oliveri.

Living for just one year,

it's her first and only summer.

This pool is her lifeline,

providing the oxygen she needs to breathe.

But her prey is outside...

...tantalisingly out of reach.

So what she does is astonishing.

She leaves the safety of her pool

to hunt on land.

SQUELCHING

Without a skeleton,

every movement takes huge effort.

She can survive

for just a few minutes...

...before she needs water to breathe again.

BUBBLING

What is more...

...she has competition.

Others are stripping the shores bare...

...and tensions are rising.

If she is to find a meal for herself,

she must seek out a more elusive prey,

by following a trail of rock pools inland.

They are home to leaping fish.

Blennies.

They are tying her in knots.

But this is no game.

She has burned precious energy, with nothing to show for it.

She can't give up.

Got one!

Just as she's getting the hang of it...

...she needs to breathe.

But she's made a potentially fatal error.

She has strayed dangerously far inland.

And in the midday sun...

...the rock pools she relies on...

...are evaporating.

Low on oxygen,

her skin starts to pale.

Her body diverting energy

to her vital organs.

She must get back to the water.

She's suffocating.

She flattens her body

into the last traces of water...

...breathing in just enough...

...for one last push.

The heat of summer has driven her

to the limit of survival.

But for others, the warmth

is exactly what they'd been waiting for.

On the Mediterranean coast, at this time of the year...

...the number of people can double.

Unbeknownst to them,

the warming weather has triggered

another summer gathering offshore.

Hidden at 50 metres deep,

it's only just been discovered.

Each year,

10 million circles suddenly appear

across miles of seabed.

A super-colony of fish nests.

The densest marine nesting ground ever seen.

Each one carefully dug out...

...by a dedicated single father.

For a few weeks, male pickerel fish

have the same mission.

To keep 8,000 eggs safe

until they hatch.

It's a round-the-clock job,

with no time to feed...

...because everything

wants to devour his eggs.

Some predators eat adults, too.

To protect his young,

a courageous father will risk his life.

But it's not just other species he must fear.

Two weeks without food

has left some fathers so hungry

that they're turning on their own kind.

A mob of cannibals

consuming every egg they can find.

And they're heading his way.

His stripes darken, in alarm,

as he prepares to defend his young.

He is overrun...

...but he won't go down without a fight.

Enemies dispersed,

time to check the eggs.

Many have gone...

...but a few thousand still remain...

...soon to hatch in the warming waters.

As summer reaches its peak,

the sun may shine for 19 hours a day.

That powers the growth of lush underwater meadows...

...which can grow ten times thicker than in winter.

For some, it's a feeding ground.

CLICKING

For others, a home.

A long-snouted seahorse.

Seagrass provides cover from predators.

An anchor on which to grasp.

And food...

...right on his doorstep.

There's just one thing missing.

He is alone.

If he's to find a mate,

he will need to venture into unknown waters.

But he has travelled no more than 20 metres

in his adult life so far.

Until recently,

this area of Portugal

was one vast grassland.

But in the last two decades,

it's been torn apart

by anchors and fishing boats.

Once home to the highest density of seahorses on Earth,

90% have now disappeared...

...leaving many without a mate.

Out here in this wasteland,

there is nowhere to hide.

Staying off the menu is one thing,

catching food is quite another.

There is little here

except hermit crabs.

But unlike normal prey,

the hermits have armour.

HEAVY THUMP

Nothing...

...but a mouthful of sand.

Swimming in open water is exhausting.

Their fins are not built

for a journey like this.

And without seagrass to act as a buffer...

...currents can double in strength.

The search for a mate

seems hopeless...

...but there could be a lifeline.

Scientists are creating shelters

for those who have lost

their seagrass homes.

For a lucky few,

these seahorse hotels offer sanctuary...

...and a chance to meet a new mate.

The oceans are being changed

not just by the seasons,

but also, by us.

With the right support,

animals can adapt,

even in our busiest waters.

Autumn in New York City.

The growth of this metropolis in the 1800s

was fuelled from a surprising source.

Fish called menhaden.

Harvested for their oil,

by the 20th century,

their numbers had crashed.

But in 2013,

when fishing quotas were set,

something remarkable happened.

A resurgence quicker than we ever thought possible.

Along America's busiest coastline,

billions of fish now swarm.

And following close behind...

...huge pods

of bottlenose dolphins...

...over 50 species of shark...

...and even...

...ocean giants.

Just 15 years ago,

only four humpbacks could be seen off New York City.

Now up to 150 of them

feast throughout the autumn...

...reconnecting urban residents with nature.

Across the globe, animals of the seasonal seas...

...show remarkable adaptability.

A ray of hope

in a rapidly transforming ocean.

The Blue Planet team are in Chile...

...to film huge waves

due to hit this coastline.

We're currently playing a little bit

of a waiting game with a weather system that's happening

half a world away. So this storm front

that's happening in Alaska right now

is going to cause the waves

that travel all the way across

the Pacific and hit the coast

of Chile, right on this beach.

The crew plan to document

how seasonal storms

impact the local sea lions.

This is one of the biggest breeding colonies in Chile.

So there's 3,000 sea lions on that rock.

They've been returning here

for generations.

But in just 60 years,

extreme weather events

are hitting four times as often.

Look at the waves.

Looks big.

The five-metre waves arrive

with the full force of the Pacific behind them.

The crew quickly begin capturing some dramatic scenes...

...but it isn't long before they realise

another story is developing.

PUP WAILS

Oh!

DISTRESSED WAILS

In the turmoil,

newborn pups are being swept away

from their mothers.

It's gone.

DISTRESSED WAILS

They're too young to be in the water.

They usually go for their first swim when they're, like,

three weeks, four weeks old, but not when they're a few days old.

So they pretty much have very little chance.

PUP BARKS

Weak and exhausted,

some are washed up.

The youngest pups won't last for more than a few days

without their mothers' milk...

...and the crew know it.

They have a really specific

call and response with their mothers.

HIGH-PITCHED WAIL

And at low tide, they're so close to the colony

that they can actually hear their mothers calling.

LOUD WAILS

They just don't have the strength to swim back.

So, yeah, it's a little bit heartbreaking.

Mothers search, but can't hear their pups

above the noise of the colony.

BARKING

And territorial males threaten any

that do attempt to leave.

DEEP GROWLING

The pups are stranded.

PUP BARKS

CODEFF, a local charity, arrives.

Suited up to keep human scent from the pups,

they bring them to a pen

to recuperate.

BLEATING

The crew pause the main shoot to film the rescue operation.

The pups need their mothers' milk,

but the rescuers can't return them

until the sea calms.

The warming oceans

have made storms more intense.

The team must rescue as many as

70 pups in a single day. PUP BARKS

As the storm rages on...

...volunteers work through the night.

Mira. Papi.

These guys are doing 24-hour shifts

right now because the waves are so high.

In the darkness,

everyone must be hypervigilant

to prevent being washed away.

They're expecting a lot of pups.

It seems like it's going to be

a pretty crazy night.

In the morning...

...the ocean is still too rough

to return the pups by boat,

so they must select the strongest ones

to release from shore.

They've waited till low tide,

which means that the distance the pups have to travel back to

the rock is much less,

so it's their best chance.

PUP BLEATS

Despite the shorter distance,

half can't make it back.

They've tried to release this pup,

but it just keeps coming back to the beach,

so I think it's too tired.

After two more days,

the swell drops just enough

for a last-chance release by boat.

This way, they hope to get them

a bit closer to the rock, so that

the weakest ones, hopefully, will get reunited with their mothers.

They're all swimming to the rock right now.

They're on their way.

DEEP BARKING

Some of the adults are sort of helping them get

towards the rock, which is really sweet.

It's looking good!

BARKING AND BLEATING

Yes. Si. Yes! HE CHUCKLES

With a little help from the adults,

all of the pups make it back

and can reunite with their mothers.

BLEATING

It's been incredible to be able

to see what CODEFF do here,

and they might have a chance now.

So there's hope for the future, in that sense.

Next time:

Polar waters...

...driving currents

across the globe...

...and bringing opportunities...

...far beyond the ice.

Explore our changing oceans with

the Open University's free poster.

To order, call...

...scan the QR code, or visit...

♪ Into the deep, I wanna see beyond the light

♪ Look to the blue, it's calling you

♪ Oh, what a sight!

♪ Awooohooo

♪ Ahhh, ahhh

♪ I hear the seas cry. ♪