Original subtitles

DAVID ATTENBOROUGH: The power of the sun drives the seasons,

transforming our planet.

Vast movements of ocean and air currents

bring dramatic change throughout the year.

And in a few special places, these seasonal changes

create some of the greatest wildlife spectacles on Earth.

The seas along the Pacific coast of North America

can be some of the richest on the planet.

These coastal waters create the perfect conditions

for the greatest explosion of life on Earth.

It's driven by some of the tiniest creatures.

As their numbers multiply, they feed vast shoals of fish,

which in turn provide food for ever larger hunters.

Billions of lives will be shaped by this immense bloom.

And the mightiest hunter of them all

has devised a remarkable way to harvest this great feast.

It's January.

Both land and sea are locked in the depths of winter.

(BIRDS CAWING)

The seas along the coast of Alaska and British Columbia

can become the richest on Earth.

But for the moment, they lie dormant.

The time of great feasting is many months away,

and a number of magical changes must first take place.

The most crucial change will be driven by the sun.

But now it is weak and offers little to those trapped here for winter.

This coastline, a maze of islands and inlets

carved by glaciers, will also shape this great event.

For now, it remains shrouded in cold.

Only the toughest can survive.

(WIND BLOWING)

Steller's sea lions huddle together to share warmth.

It's 1 5 degrees below zero.

They have little choice but to suffer this,

the coldest Alaskan winter on record.

The shoals of fish they depend on

spend winter in the deepest water.

(SEA LION GRUNTING)

For now the fishing is hard.

(SEA LION GRUNTING)

It's an unforgiving place to raise a family.

Conditions are so severe

that mothers must suckle their young for up to three years.

For this pregnant sea lion, the risks are even greater.

The seas must come to life in good time

for the arrival of her pup,

and at this stage, the odds don't look good.

(WIND HOWLING)

For now, all she can do is wait

for the sun to bring change.

These seas have the potential

to be so rich at the height of the great feast,

that they will attract animals from across the vast Pacific.

And 3,000 miles away in the waters of Hawaii,

another mother is about to embark on an epic journey.

(HUMPBACK WHALE SINGING)

This humpback whale has already given birth.

Her calf is just a few weeks old.

He stays close to his mum.

(HUMPBACK WHALES SINGING)

The difference between Hawaii and Alaska could hardly be greater.

These are calm, warm waters with few predators,

an ideal nursery for the youngster.

The calf is now drinking

400 litres of milk every day,

building up strength

for the long voyage he'll soon have to undertake.

More than 5,000 humpbacks come to Hawaii each year.

The males, lured here in the hope of mating,

compete among themselves with great shows of strength.

But none of these whales can actually feed here,

for these tropical waters are comparatively lifeless.

(WHALE ROARING)

The ocean's greatest riches

are only to be found in colder seas.

So all these whales must return to the North Pacific to feed.

The playful calf suckles from his mother every day.

But she hasn't had anything to eat

since she left Alaska over four months ago,

and she won't feed again until she returns.

Like the pregnant sea lion,

this mother has to get her timing right.

She must arrive in Alaska for the moment when the seas

are at their richest, full of fish.

Their journey north will take three months.

Back in Alaska, the seas are starting to awaken.

It's March, and as the sun gathers strength,

winter loosens its grip.

For the sea lions, things are beginning to look up.

The sun is drawing life from the depths.

(SEA LIONS BLOWING AIR)

With each passing day, the sun warms the water for longer,

penetrating deep into the mineral-rich waters.

Fertilising nutrients of phosphorous and nitrogen

fuel a miraculous change that is just beginning.

Empty seas start to come to life.

As we enter an enhanced view of this microscopic world,

we see the beginnings of a magical transformation.

Phytoplankton, tiny floating plants, emerge.

Each is scarcely bigger that a speck of dust.

But together, these plankton will bloom in such immense numbers

that they transform lifeless seas.

And whether that will happen this year is yet to be determined.

All creatures here, from the sea lions to the migrating whales,

ultimately depend on these miniature plants.

For one creature that relies directly on the plankton,

this is the moment to emerge.

Pacific herring have spent the winter in the depths of the fjords,

but they now rise up and head for the shallow coast.

Stimulated by the sun and the warming water,

they gather in their hundreds of millions.

But they're not drawn here to feed.

They're following an irresistible urge to breed.

Groups of males sweep through the shallows

and release their sperm in vast, milky clouds.

The females follow, covering the seabed with eggs.

Such a concentration of fish

is just what the sea lions have been waiting for.

The herring won't be here for long.

The sea lions must make the most of the fishing while it lasts.

Other predators gather, also hungry after the lean winter.

This short-lived bounty

is a magnet for millions of migrating birds.

This is just the first brief course in the great feast.

The herring spawning will be over in a matter of days,

and the shoals of fish will then scatter along the coast.

The herring have spawned on an astonishing scale.

They turn hundreds of miles of coastline white with spawn.

In this bay alone,

they have laid 800 billion eggs.

The herrings' spawning is so timed

that when the next generation hatch in a few weeks

they'll be able to feed on the growing plankton.

And this year, the herring appear to have timed it just right.

The minute plant plankton,

the driving force behind the seas' transformation,

are starting to bloom.

Great swathes of sea grow green with life.

The humpbacks are still out in the middle of the Pacific.

They've missed the first taste of the great feast.

At just eight weeks old,

the young calf must cross the biggest ocean in the world.

His mother will only swim as fast as her young calf.

As he tires, she supports him from beneath.

She's been living off her fat reserves

for the last six months,

and has lost a third of her body weight.

She's close to starving.

(WHALES SPOUTING WATER)

It will be a further two months before mother and son

reach their feeding grounds in the North Pacific.

It's May, early summer in Alaska,

and the days are getting ever longer.

The sun continues to fuel the growth of microscopic plants

that make up the plankton bloom.

They're joined by a growing community of tiny animals...

zooplankton.

These are the first creatures to feed on the bloom.

Over the coming months they will multiply,

crowding the surface waters in their trillions.

The next stage of the great feast is underway.

All life here depends on this plankton bloom.

The herring feed on it directly.

The greater the bloom, the more abundant the shoals.

And the fish themselves become food for the larger hunters.

But the shoals of herring are now spread far and wide,

and once again, for the sea lions

the fishing is tough.

They must venture further to find food.

But open water is a risky place to fish.

This male sea lion hunts alone.

He is three metres long and a ton in weight.

Few would dare tackle him.

(SEA LION BLOWS AIR)

The smaller females travel as a group,

keeping a watchful eye in all directions.

They know that killers lurk in the depths.

The surface is a dangerous place to linger,

especially if you're alone.

Orca. Killer whales.

The sea lion is wounded, but the killers keep their distance.

His powerful jaws are still a threat to the hungry orca.

He struggles towards the safety of land.

But his injuries are slowing him down.

(ORCA CRASHING)

Blow by blow, they wear him down.

It's a carefully coordinated attack.

One killer distracts his attention,

while another hits his soft underside.

(ORCA CRASHING)

The richest seas on Earth can be treacherous.

Orca attacks, although savage,

have little impact on the fate of most sea lions.

Their survival depends more on the tiny plankton

that sustains the great shoals of fish on which they feed.

It's now late May.

The sunlight lasts for 1 7 hours a day.

But the bloom will need more than just sun

if it's to reach its full extent.

Nutrients held in these waters are continuously used up

as the bloom increases.

If they're exhausted too early,

the plankton will die and the food chain will collapse.

The effects will be felt by all.

Meanwhile, on the sea lion colony,

new life is now arriving.

After a year carrying her pup,

this mother can at last give birth.

(SEA LIONS GRUNTING)

The pup is utterly dependant on his mum.

As he makes sense of his new world,

she encourages him to take his first feed of milk.

The mother has waited until early summer to have her baby -

such a small pup would never survive the winter.

Along this coast,

thousands of pups are born within a matter of weeks,

timed to coincide with the better conditions that may lie ahead.

(SEA LIONS GRUNTING SOFTLY)

The migrating humpbacks are still weeks away from Alaska

and their first meal.

(WHALE BLOWING AIR)

In these turbulent seas,

mother and calf must stay close.

A huge Pacific storm is brewing

and heading straight for the coast of British Columbia.

(WAVES CRASHING)

Directly in its path lies the sea lion nursery.

The pups are now at the mercy of the elements.

The mothers must get their young to the safety of higher ground,

if they can find it.

(WAVES CRASHING)

In desperation, a mother tries to drag her pup away

from the gathering tempest.

A pup swept into the water

is unlikely to be seen again.

As the seas begin to subside, many have survived.

But others have not.

There's nothing this mother could have done to save her pup.

These mighty storms, though devastating for some,

bring fresh life to the great feast.

(WATER RUSHING)

When these storms hit the coast,

they stir up vital nutrients

into the surface waters, nutrients that feed the plankton.

Replenished seas combine with the lengthening days

to create a plankton explosion.

And this has come just in time

for those at the end of an incredible journey.

The humpbacks have arrived.

After 3,000 miles, mother and calf

have finally made it to the coast of Alaska.

They join other whales that have also made the long voyage.

But their journey isn't over, for they have yet to feed.

They're heading for a particular stretch of coast

deep in the network of channels,

where they know they can find the great shoals of herring.

It's to these ancestral feeding grounds

that the mother now guides her new calf.

The unique geography of this coastline

holds the final secret to this great event.

Glaciers have carved a landscape

of deep fjords and islands over tens of thousands of years.

This patchwork creates a labyrinth

through which powerful ocean and tidal currents flow,

bringing up the vital raw ingredients needed for the bloom.

It's as if an endless supply of fertiliser

is being added to the water.

In other seas, the plankton would be subsiding by now.

But here the seas are repeatedly invigorated,

which fuels the plankton bloom

time and again throughout the summer.

And with the sun at its most powerful,

all these elements combine

to create a plankton bloom of great intensity.

In July, the ocean is alive.

This floating community of plants and animals

is the basis for all life here,

and a bloom of this intensity

signals the start of a truly great feast.

Where this rich soup hits the sea bed,

life carpets every available surface.

The feasting begins with millions of tiny mouths.

Barnacles sift morsels of plankton brought in on the currents.

Many of these creatures started their lives

as part of the plankton before reaching adulthood

and settling on the sea floor.

These animals are giants.

They filter the plankton-rich water,

growing larger here than anywhere else in the world.

Jellyfish gather, forming great swarms.

They, too, eat the plankton, rising to the surface

where it is at its most abundant.

By late summer, the plankton bloom is so vast

it radiates across the North Pacific.

Blooms like these provide Earth with over half of its oxygen.

This bloom eclipses even the Amazon rainforest

in sheer abundance of plant life.

And it is most intense

where the ocean streams through the maze of coastal waterways.

The shoals of herring are now at their most plentiful.

After feeding through the summer months,

the fish themselves are a good catch,

the main target for predators now gathering here.

After enduring the bitter winter,

the sea lions can enjoy the bounty they've been waiting for.

Hunting together, they drive the herring to the surface.

Then, with mesmerising grace,

they pick off fish one by one.

For a few short weeks,

they'll have their share of the great feast.

Others arrive to feed in the coastal waterways.

(DOLPHINS CLICKING)

Pacific white-sided dolphins.

They dart in and snatch fish as they go.

The tidal currents now sweep herring up to the surface.

Here, they're within diving range of sea birds.

Murres are the first to find the fish.

The shoal twists and turns,

trying to escape the surface dangers.

But murres are so fast they can even out-swim the herring.

They head off the escape,

making the shoal turn in on itself, creating a bait ball.

The birds corral the herring

into an ever-tighter ball.

But the commotion hasn't gone unnoticed.

Gulls, ever the opportunists, are the next to turn up.

They can dive no more than a metre,

so the fish are still out of reach.

The murres only attack from beneath,

trapping the fish against the surface.

But they push the herring within range of the gulls.

It's a feeding frenzy.

The table is set for the mightiest predator of them all.

The humpbacks have reached their feeding grounds.

After six months without a bite to eat,

the humpbacks can finally break their fast.

The whales have learned to target these ready-made balls of fish.

But they'll need more than just a mouthful,

and with the feast now in full swing,

this is their chance.

To exploit the vast shoals of herring that are in deeper water,

they rely on teamwork.

For these whales have developed a truly remarkable way of hunting.

(WHALES SINGING)

The inlets echo to the sound of a mysterious song.

(WHALES SINGING)

A curtain of bubbles

and a haunting call hold the secret

to an ingenious way of fishing.

(WHALES SINGING)

(HIGH-PITCHED SINGING)

This is ''bubble-net feeding''.

A dozen whales work together to harvest the herring bonanza.

Such fishing requires an extraordinary level

of intelligence and cooperation.

The lead whale dives first.

She is the bubble-blower.

It's her job to find the fish.

(WHALE SPOUTING AIR)

The rest follow in formation.

Each takes exactly the same position in every lunge.

Once she's located the fish,

the leader blows a net of bubbles

that completely encircles the shoal.

(WHALE SINGING)

Another whale calls to synchronise the group.

(WHALE SINGING CONTINUES)

Panicked by the eerie sound and the blinding bubbles,

the fish won't cross this fizzing curtain.

(HIGH-PITCHED SINGING)

As few as 1 00 humpbacks

have learnt how to feed as a team like this.

And this is the only place on the planet where whales fish in this way.

(LOUD MOANING)

At the height of the great feast,

these humpbacks fish around the clock,

each eating a ton of herring a day.

Only man has learnt to exploit the seas

on a greater scale.

As the summer ends, the feast draws to a close.

The sun is weakening,

and with it, the plankton bloom subsides.

The microscopic plants that brought life

to empty seas begin to die.

The herring descend to spend the winter in the depths.

Life for the sea lions will be harder once again.

But they've fed well enough to face the dark days ahead.

(WHALES SPOUTING AIR)

The humpback whales will soon leave these shores.

It's astonishing to think that

some of our world's mightiest creatures

ultimately rely on some of its tiniest.

Here, along the North Pacific coast,

the interplay between land, sea and sun

has produced a bloom of plankton so immense

it has created one of nature's great events.