Introduction The Blue Planet

Dwarfed by the vast expanse of the open ocean,

the biggest animal that has ever lived on our planet.

A blue whale, 30m long and weighing over 200 tonnes.

It's far bigger than even the biggest dinosaur.

Its tongue weighs as much as an elephant,

its heart is the size of a car

and some of its blood vessels are so wide you could swim down them.

Its tail alone is the width of a small aircraft's wings.

Its streamlining, close to perfection,

enables it to cruise at 20 knots.

It's one of the fastest animals in the sea.

The ocean's largest inhabitant

feeds almost exclusively on one of the smallest -

krill, a crustacean just a few centimetres long.

Gathered in a shoal, krill stain the sea red.

A single blue whale in a day can consume 40 million of them.

Despite the enormous size of blue whales

we know very little about them.

Their migration routes are still a mystery

and we have no idea where they go to breed.

They are a dramatic reminder of how much we still have to learn

about the ocean and the creatures that live there.

Our planet is a blue planet.

Over 70% of it is covered by the sea.

The Pacific Ocean alone covers half the globe.

You can fly across it for 12 hours

and still see nothing more than a speck of land.

This series will reveal the complete natural history of our ocean planet,

from its familiar shores to the mysteries of its deepest seas.

THEY SHRIEK

By volume, the ocean makes up 97% of the Earth's inhabitable space.

Its marine life far exceeds that which inhabits the land.

But life in the ocean is not evenly spread.

It's regulated by the path of currents carrying nutrients

and the varying power of the sun.

In this first programme we'll see how these two forces interact

to control life from the coral seas...

..to the polar wastes.

SEA LION ROARS

The sheer physical power of the ocean dominates our planet.

It profoundly influences the weather of all the world.

Water vapour rising from it forms the clouds

and generates the storms that ultimately will drench the land.

The great waves that roar in towards the shores

are dramatic demonstrations of its power.

Waves originate far out at sea.

There, even gentle breezes can cause ripples

and ripples grow into swells.

Out in the ocean, unimpeded by land, such swells can become gigantic.

It's only when an ocean swell eventually reaches shallow water

that it starts to break.

As it approaches the coast,

the bottom of the swell is slowed by contact with the sea bed.

The top of the swell, still going fast, starts to roll over

and so the wave breaks.

The ocean never rests.

Huge currents such as the Gulf Stream,

keep its waters on the move all round the globe.

These currents, more than any other factor,

control the distribution of nutrients and life in the seas.

A tiny island lost in the midst of the Pacific.

It's the tip of a huge mountain that rises from the sea floor below.

The nearest land is 300 miles away.

Isolated sea mounts like this one create oases

where life can flourish in the comparatively empty expanses of the open ocean.

But the creatures that swim beside it would not be here were it not for one key factor -

the deep ocean currents.

Far below the surface,

they collide with the island's flanks and are deflected upwards,

bringing from the depths, a rich soup of nutrients.

Such upwellings attract great concentrations of life.

Most of the fish here are permanent residents feeding on the plankton,

tiny plants and animals nourished by richness brought from the depths.

They in turn attract visitors from the open ocean.

Tuna.

The plankton feeders are easy targets.

All this action attracts even larger predators.

Sharks.

Hundreds of sharks.

These silky sharks are normally ocean-going species,

but the sea mounts in the eastern Pacific,

like Cocos, Malpelo and the Galapagos,

attract silkies in huge groups, up to 500 strong.

Silkies specialise in taking injured fish

and constantly circle sea mounts looking for the chance to do so.

But silkies are not the only visitors.

Hammerheads gather in some of the largest shark shoals to be found anywhere in the ocean.

Sometimes thousands will circle over a single sea mount.

But these sharks are not here for food.

They have come for another reason.

Some of the locals provide a cleaning service.

Following the last El Nino year,

when a rise in water temperatures caused many sharks to suffer from fungal infections,

the number of hammerheads at the sea mounts reached record levels.

Nutrients also well up to the surface along the coasts of the continents.

This is Natal on South Africa's eastern seaboard.

It's June, and just offshore

strange, black patches have appeared.

They look like immense oil slicks up to a mile long.

But this is a living slick -

millions of sardines on a marine migration

that in sheer biomass rivals that of the wildebeest on the grasslands of Africa.

Most of the time these fish live in the cold waters south of the Cape.

But each year, the coastal currents reverse.

The warm Agulhas current that flows from the north has been displaced

by cold water from the south and has brought up rich nutrients.

They in turn have created a bloom of plankton

and the sardines are now feasting on it.

As the sardines travel north, a caravan of predators follow them.

Thousands of Cape gannets track the sardines.

They nested off the Cape

and timed their breeding so their chicks can join them in pursuing the shoals.

Below water, hundreds of sharks have also joined the caravan.

These are bronze whaler sharks,

a cold-water species that normally lives much further south.

These three-metre sharks cut such swathes through the sardine shoals

that their tracks are clearly visible from the air.

Harried by packs of predators and swept in by the action of the waves,

the sardine shoals are penned close to the shore.

Common dolphin are coming in from the open ocean to join the feast.

There are over a thousand of them in this one school.

When they catch up with the sardines, the action really begins.

Working together, they drive the shoal towards the surface.

It's easier for the dolphins to snatch fish up here.

Now the sardines have no escape.

Thanks to the dolphins, the sardines have come within the diving range of the gannets.

Hundreds of white arrows shoot into the sea

leaving long trails of bubbles behind each dive.

Next to join the frenzy are the sharks.

Sharks get very excited around dolphins,

maybe because they can feed well,

once the dolphins drive the sardines into more compact groups near the surface.

As the frenzy continues, walls of bubbles drift upwards.

They are being released by the dolphins, working together in teams.

They use the bubbles to corral the sardines into ever tighter groups.

The sardines seldom cross the wall of bubbles

and crowd closer together.

Bubble netting enables the dolphins to grab every last trapped sardine.

Just when the feasting seems to be almost over, a Bryde's whale.

The survivors head on northwards

and the caravan of predators follows them.

Nutrients can also be brought up, though less predictably, by rough weather.

Particularly near the Poles, huge storms stir the depths

and enrich the surface waters.

And here in the south Atlantic, the seas are the roughest on the planet.

And very rich seas they are too.

The cold Falklands current from the south

meets the warm Brazil current from the north.

At their junction, there is food in abundance.

These black-browed albatross are diving for krill that has been driven up to the surface.

Like all albatross, black-brows are wanderers across the open ocean.

A feeding assembly on this scale is a rare sight.

Usually, the birds of the open sea are widely dispersed.

But these feeding grounds are close to an albatross breeding colony,

and a very special one.

This is Steeple Jason, a remote island in the west of the Falklands.

It has the largest albatross colony in the world.

There are almost half a million albatross here,

an astonishing demonstration of how fertile the ocean can be

and how much food it can give even to creatures that don't live in it.

LOUD CAWING OF BIRDS

Not only nutrients generate these vast assemblies.

The heat and light that the sun brings

is essential for the growth of microscopic floating plants,

the phytoplankton.

And it's the phytoplankton that is the basis of all life in the ocean.

Every evening, the disappearance of the sun below the horizon

triggers the largest migration of life that takes place on our planet.

1,000 million tonnes of sea creatures rise from the deep ocean

to search for food near the surface.

They graze on the phytoplankton under cover of darkness.

Even so, they're far from safe.

Other marine hunters follow them,

some travelling up from hundreds of metres below.

At dawn, the whole procession returns to the safety of the dark depths.

The moon too has a great influence on life in the oceans.

It's gravitational pull creates the advances and retreats of the tide.

But the moon has more than a daily cycle.

Each month it waxes and wanes as it travels round the Earth.

This monthly cycle also triggers events in the ocean.

The Pacific coast of Costa Rica, on a very special night.

It's just after midnight and the tide is coming in.

The moon is in its last quarter,

exactly halfway between full and new.

For weeks the beach has been empty, but that is about to change.

At high tide, turtles start to emerge from the surf.

At first they come in ones and twos.

But within an hour, they are appearing all along the beach.

They are all female Ridleys turtles

and over the next six days or so, 400,000 will visit this one beach

to lay their eggs in the sand.

At the peak time, 5,000 are coming and going every hour.

The top of the beach gets so crowded that they have to clamber over one another

to find a bare patch where they can dig a nest hole.

A quarter of the world's population of Ridleys turtles come to this one beach

on a few key nights each year.

The rest of the time, they're widely distributed, searching for food,

most hundreds of miles from here.

This mass nesting is called an arribada.

How it's coordinated is a mystery

but we do know that arribadas start

when the moon is in its first or its last quarter.

40 million eggs are laid in just a few days.

By synchronising their nesting in this way,

the females ensure that six weeks later their hatchlings will emerge in such enormous numbers

that predators on the beach are overwhelmed and a significant number of baby turtles will survive.

But why do the females use a cue from the moon to help them synchronise their nesting?

Part of the answer to that becomes clear at dawn,

on the following morning.

The day shift of predators are arriving for their first meals.

Vultures have learnt that the returning tide

can wash freshly-laid eggs out of the sand.

The risk of eggs being exposed by the surf

may be part of the reason why turtle arribadas tend to occur

around the last or first quarter of the moon.

It's on days such as this, when the moon is neither full nor new,

that the tides are weakest and the sea is likely to be calmer.

So at these times it's easier for the female turtles

to make their way through the surf

and there's less chance of their eggs

being washed out of the sand and being taken by the vultures.

The moon's monthly cycle, and its influence on the tides,

triggers many events in the ocean,

from the spawning of the corals to the breeding cycles of fish.

But an even longer rhythm has the most profound effect of all -

the annual cycle of the sun.

The sun's position relative to the Earth changes through the year

and this produces the seasons.

In the north, Spring comes as the sun rises higher in the sky.

Off the coast of north-west America, the seas are transformed

by the increasing strength of the sunshine.

Here in Alaska, the coastal waters turn green

with a sudden bloom of phytoplankton.

Herring that have spent the winter far out to sea,

time their return to the shallow waters

to coincide with this bloom.

Their vast numbers start one of the oceans' most productive food chains.

Humpback whales are at the top of that food chain.

They spent the winter breeding in warmer tropical waters off Hawaii.

But there was little food for them there.

This herring bonanza provides the majority of their food for the year.

Stellar and Californian sea lions also return from the open ocean each year to feast off the herring.

The herring themselves, however, have not come here for food.

They are about to breed.

Nothing deters them as they head for even shallower waters.

Now the waters are so shallow that glaucous-winged gulls

snatch live fish from the surface.

In spite of these attacks and losses, the herrings swim on

until they reach the vegetation the females need if they are to lay.

Each female produces around 20,000 eggs.

And they're very sticky.

The males arrive soon after the females have spawned

and release their sperm in vast milky clouds.

Soon the excesses of the herrings' sexual spree

creates a thick white scum on the surface.

Through the season,

curds of sperm clog the shores for hundreds of miles,

from British Columbia in the south all the way to Alaska in the north.

After a few days, this gigantic spawning ends

and the herring head back out to deeper waters,

leaving behind them fertilised eggs plastered on every rock and strand of vegetation.

They time their spawning

so that two weeks later, when these eggs start to hatch,

the annual plankton bloom will have reached its height and the new-born fish fry will have plenty to eat.

Meanwhile, all these eggs provide food for armies of animals

both below and above the surface.

Millions of birds arrive to collect a share of the herrings' bounty.

Some of it is easily gathered, for millions of eggs have been washed up onto the shore.

This encapsulated energy is particularly valuable to migrating birds.

These surf birds are on the way to breeding grounds in the Arctic

and they had to come down to refuel.

Stranded herring eggs are just what they need.

Bonaparte's gulls collect the eggs just below the surface of the water.

Further out in the bay,

huge flocks of ducks gather. They're mostly surf scoters -

diving ducks that can feed off the bottom several metres down.

There are such huge quantities of eggs,

that even such a big animal as a bear finds it worthwhile to collect them.

The spawning of the herring is a crucial event in the lives of many animals all along the coast.

The whole event coincides with the plankton bloom

and within three weeks it's all over.

The migratory birds leave to continue their journey north.

They will not come back until the herring also return next year.

As the herring spawning finishes,

other migrants are starting to arrive, just off shore.

Grey whales.

They have followed the sun north

and they too are seeking the food generated by the bloom of the phytoplankton.

Krill are feeding off it

and these whales are feeding on the krill,

skimming it from the surface with the filter plates of baleen

that hang from their upper jaws.

Grey whales make one of the longest migrations of any marine mammal -

a round trip of 12,000 miles or so,

from their breeding grounds off Mexico, along the entire coast of North America to the Arctic Ocean.

They travel close to the coast, with the males and non-breeding females leading the way.

The last to start are the cows that have just given birth.

They have to wait until their new-born calves are sufficiently big and strong.

Their progress is necessarily slow.

The mothers must stay alongside their young and even a strong calf can only travel at two knots.

They stick even closer to the shore,

often within just 200 metres.

Killer whales.

They have learnt that grey whales follow traditional routes.

The killers have no trouble in overtaking a calf and its mother.

Normally, they continually call to one another

but now they have fallen silent.

The mother grey whale and her calf have no idea

that they've been targeted.

Catching up with the grey whales is the easy part for the killers.

They have to be cautious for they are only half the size

of the grey whale mother. She can inflict real damage with her tail.

But the killers are not after her. They're after her calf.

As long as the mother can keep it on the move, it will be safe.

She does her best to hurry it along.

At first, the killers avoid getting too close to the mother, but just keep pace alongside.

They know that the calf, going at this speed, will eventually tire.

After three hours of being harried in this way,

the calf is too exhausted to swim further. The mother has to stop.

This is the moment the killers have been waiting for.

They try to force themselves between mother and calf.

A calf separated from its mother will not be able to defend itself.

Time and again, the black fins of the killers appear

between the mottled backs of the grey whales.

At last, the killers succeed,

and now that they have the calf on its own, they change their tactics.

They leap right onto the calf and try to push it under.

They're trying to drown it.

The calf snatches a desperate breath.

The mother becomes increasingly agitated.

Frantically she tries to push her calf back to the surface so that it can breathe.

But now it's so exhausted that it has to be supported by its mother's body.

The killers won't give up.

Like a pack of wolves, they take turns in harassing the whales.

Now the whole pod is involved.

One of them takes a bite.

Soon the sea is reddened with the calf's blood

and the killers close in for the final act.

The calf is dead.

After a six-hour hunt, the killer whales have finally won their prize.

The mother, bereft, has to continue her migration north on her own.

She leaves behind the carcass of a calf that she cherished

for 13 months in her womb, for which she delayed her own journey to find food.

The pod of 15 killer whales spent over six hours trying to kill this calf, but now, having succeeded,

they've eaten nothing more than its lower jaw and its tongue.

Valuable food like this will not go to waste in the ocean.

Before long, the carcass will sink to the very bottom of this deep sea.

But even there, its flesh will not be wasted.

Over a mile down, in the total darkness of the deep ocean,

the body of another grey whale, a 30-tonne adult.

It settled here only a few weeks ago.

Already it has attracted hundreds of hackfish.

These scavengers, over half a metre long and as thick as your arm,

are only found in the deep sea.

They have been attracted by the faint whiff of decay suffusing through the water for miles around.

With their heads buried in the whale's flesh,

they breathe through gill openings on their sides.

They're very primitive creatures,

not even true fish for they lack jaws.

They feed not by biting,

but by rasping off flesh with two rows of horny teeth.

In just a few hours, a hackfish can eat

several times its own weight of rotting flesh.

Next to arrive, a sleeper shark.

It moves so slowly to conserve energy -

an important strategy for so large an animal surviving in such a poor habitat.

Sleeper sharks live over a mile down

and grow to over seven metres long.

They can go for months without food, cruising along the bottom, waiting for rare bonanzas,

such as this one, to arrive from above.

A whole range of different deep-sea scavengers

will feast on this carcass for a long time, before all its nutriment has been consumed.

18 months later, all that is left is a perfect skeleton stripped bare.

The sun's energy that was captured and turned into living tissue by the phytoplankton

has been transferred from one link to another in the food chain

and ended up as far away from the sun as possible on this planet,

at the bottom of the deep sea.

But some energy also returns from the deep.

Millions of opalescent squid

are on their way to the shallows. They've come up here to mate.

As the males grab the females, their tentacles flush red.

For most of the year, these squid live at a depth of about 500 metres.

They only come together for a few weeks.

Just one school was estimated to contain animals that weigh around 4,000 tonnes.

Wave after wave rise from the depths,

and soon the sea-bed and shallows are strewn with dense patches of egg capsules several metres across.

As each female adds another capsule to the pile,

the males fight to fertilise its contents.

The squid make their huge journey into the shallows

because their eggs will develop faster in the warmer water here.

When the young emerge, they will find food more easily than they would in the ocean depths.

Dawn the next morning,

and the sea-bed for miles around is covered in egg capsules.

The squid themselves have all gone.

Many will have died but some have returned to their home in the deep.

They will not return to the light of the sun

until the next time they are driven up by the urge to spawn.

The enormous size of the oceans,

and the fact that we know so little about many of the creatures there,

have presented the film makers behind the Blue Planet series with difficult challenges.

None more so than the mighty blue whale.

Despite their massive size, blue whales have hardly ever been filmed.

And there are good reasons for that. They're among the fastest marine creatures. Faster than many boats.

Except for a few minutes to breathe, they stay submerged.

Even when they surface, they're timid and difficult to approach.

So, to capture blue whales on film is very difficult,

and it took the team many months and some ingenuity,

just to get these few rare images.

Just finding and keeping up with blue whales is a real challenge.

One of the largest blue whale populations migrates back and forth,

along the coast of California and Mexico each year.

For three seasons our camera teams were on standby,

waiting for passing whales.

In theory, a microlite is perfect for filming. It's inexpensive,

it doesn't disturb the whales and it's possible to land and dive in the water.

But as the migration continued south,

the whales were soon out of range and another strategy was called for.

We followed the whales south to Mexico and the Gulf of California.

On several consecutive years recently, blue whales have been regularly sighted here,

and the Gulf's calm waters seemed an ideal location for filming.

However, getting close enough to get film images wasn't going to be easy,

as experienced cameraman, Rick Rosenthal explains.

Filming whales around the world, I think that they are like either

a large aeroplane or... Very streamlined and it's difficult

to get an image. You're going to have to be very patient, if you're gonna get any behaviour whatsoever.

'Mary Lee, Mary Lee, Santa Emily, come back?'

The first problem was to find the whale

in 30,000 square miles of water.

OK, yes, you're just turning around the moon for us,

that's beautiful.

Using the locations of previous sightings, the team enlisted

the help of experienced pilot Sandy Lanham, who had a trained eye for spotting blue whales from the air.

I've been working with scientists for whale research for 10 years.

We're convinced that the only way to cover a body of water this large, is to use an aeroplane.

Without directions from the air,

the team would have found it far harder to catch up with the whales.

Once the boat had gained visual contact with the blue whale,

they aimed to get a good shot as it came up for air.

It was essential not to cause any disturbance.

The trick was to try and sneak ahead of the whale, predicting where it would surface next.

You need special permission and a good deal of experience to get this close to whales.

I dove down

and could see a white glowing body and turned the camera on

and the result was, you know,

a nice image of a huge blue whale

gliding by me like a giant torpedo.

Getting close to blue whales in a small boat

without causing disturbance

requires a good understanding of their behaviour.

You NEVER chase whales.

When they come up for air, their tails leave a smooth patch of water called a footprint.

These indicate its speed and direction.

If you're lucky, you can gauge where it will surface in about 15 minutes.

After countless attempts at this guessing game,

Rick was finally in the right place at the right time.

The whale was surfacing near the boat. At one time it came up close,

we were able to manoeuvre the boat quietly so we were on top of it,

looking down at it - enormous tail and the entire body stretched out,

maybe 50-60 feet long.

It's one of those Captain Ahab, Moby Dick tales

when you are looking down at the entire whale

and it was very quiet and not concerned about us.

It took some breaths and submerged and came up again

and we manoeuvred again and got in the same position.

We were looking down at the entire whale underneath us.

That's an extraordinary feeling for anybody.

Subtitles by Gabby De Gregorio and Nick Holmes - 2001

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