Original subtitles

Dwarfed by the vast expanse of the open ocean

the biggest animal that has ever lived on our planet.

A blue whale, 30 metres 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 that you could swim down them

Its tail alone is the width of a small aircraft wings

Its streamlining, close to perfection, enables it to cruise at twenty 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 and a single blue

whale in a day can consume forty 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 absolutely 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 seventy percent of it is covered by the sea

The Pacific Ocean alone covers half the globe

You can fly across it non-stop for twelve 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

By volume, the ocean makes up 97% of the earth inhabitable space

And the sheer quantity of marine life

it contains 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 will see how these two forces interact

to control the distribution of life from the coral seas ...to the polar wastes

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 open 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 water at the bottom of the swell is slowed by contact with the sea bed

The top of the swell, still travelling fast,

starts to roll over and so the wave breaks

The ocean never rests.

Huge currents, such as the Gulf Stream,

keep its waters constantly on the move all round the globe

It's these currents more than any other factor

that 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 precipitously from the sea floor thousands of metres below

The nearest land is three hundred miles away

Isolated sea mounts like this one create oases

where life can flourish...

in the comparatively empty expanses of the open ocean

But all 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 with them from the depths a rich soup of nutrients

Such up-wellings attract great concentrations of life

Most of the fish here are permanent residents,

feeding on the plankton, the tiny floating plants and animals that are nourished

by the richness brought up from the depths

And 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 five hundred strong

Silkies seem to specialize in taking injured fish

and constantly circle sea mounts on the look out 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 visiting 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 off-shore, strange black patches have appeared

They look like immense oil slicks up to a mile long

But this is a living slick

Millions and millions of sardines on a marine

migration that in terms of sheer biomass

rivals that of the wildebeest on the grasslands of Africa

These fish live for most of the time

in the cold waters south of the Cape,

but each year the coastal currents reverse

The warm Agulhas current that

usually flows down from the north

has been displaced by cold water coming up from the south

and that 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 whole caravan of predators follow them

Thousands of Cape Gannets track the sardines

They nested off the Cape

and timed their breeding so that their newly-fledged 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 great 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 is 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 when dolphins are around

That may be because they can feed particularly...

well once the dolphins have driven

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 in this way enables the dolphins to grab every last trapped sardine

Just when the feasting seems to be almost over,

a Bryde whale arrives

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, for here,

the cold Falklands current from the South

meets the warm Brazil current from the North

and at their junction there is food in abundance

These Black-browed albatross are duck-diving

for krill that has been driven up to the surface

Like all albatross,

Black-brows are wanderers across the face of the open ocean

A feeding assembly on this scale is a rare sight

Most of the time,

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 far 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 do not actually live in it

Nutrients by themselves are not enough to generate these vast assemblies.

The heat and light that the sun brings everyday

is also essential for the growth of the microscopic floating plants

- the phytoplankton

And it 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

One thousand million tones of sea creatures

ascend from the deep ocean to search for food near the surface

They graze on the phytoplankton under cover of darkness

Even so, they are 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

Its gravitational pull creates the daily advance and retreat of the tides

But the moon has more than a daily cycle

Each month it waxes and wanes as it travels around the earth,

and this monthly cycle also triggers events in the ocean

The Pacific Coast of Costa Rica on a very special night

It just after midnight and the tide is coming in

The moon is in its last quarter,

exactly half way 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 a hour,

they are appearing all along the beach

They are all female Ridley turtles

and over the next six days or so

four hundred thousand will visit this one beach

to lay their eggs in the sand

At the peak time, five thousand 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 population

of Ridley turtles come to this one beach

on a few key nights each year

The rest of the time, they are widely distributed through the ocean

searching for food, most -a hundreds of miles away from here

This mass nesting is called an arribada

How it is co-ordinated is a mystery

- but we do know that's arribadas start

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

Forty 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 proportion

of the baby turtles will get past them and make it to the water

But why do the females use a cue from the moon

to help in synchronising 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 such days 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 easier for the female turtles

to make their way through the surf

and there less chance of their eggs

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

The moon monthly cycle and its influence on the tides triggers

many events in the ocean, from the spawning of the corals

on the Great Barrier reef to the breeding cycles of fish

But there an even longer rhythm

that has the most profound effect of all

- the annual cycle of the sun

The sun position relative to the earth changes

through the year and it this that produces the seasons

In the north, spring comes as the sun begins to rise 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

They come in vast numbers and initiate

one of the most productive food chains in all the oceans

Humpback whales are at the top of that food chain

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

But there was little food for them there

This herring bonanza provides the vast 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 are able to snatch live fish from just below the surface

In spite of these attacks and losses,

the herring swim on until

they reach the vegetation that the females

need if they are to lay

Each female produces around twenty thousand eggs

- and they every 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

comes to an end 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

But in the meantime, all these eggs provide food

for armies of different animals both below and above the surface

Millions of birds arrive to collect a share of the herring 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 surfbirds are on their way

to their breeding grounds in the Arctic

and they have to come down to refuel

Stranded herring eggs are just what they need

Bonaparte gulls collect the eggs just below the surface of the water

Further out in the bay, huge flocks of ducks have gathered

They are 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 just three short weeks it 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 offshore

Grey whales

They have followed the sun north

and they too are seeking the food

that is 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

undertaken by 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

right up 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 to tackle such an immense journey

Their progress is necessarily slow

The mothers must stay alongside their young

and even a strong calf can only travel at a couple of 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 devoted 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 have been targeted

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

They have to be cautious for they are only...

about half the size of the grey whale mother

She can inflict real damage with her tail

But the killers are not after her They are after her calf

As long as the mother can keep it on the move,

it will be safe and 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 becomes too exhausted to swim any further

The mother has to stop

This is the moment the killers have been waiting for

They start to try and 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've got the calf on its own, they change their tactics

They leap right on to the calf and try to push it under

They are 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 is 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 thirteen months in her womb

for which she delayed her own journey to find food

The pod of fifteen killer whales spent over six hours trying to kill this calf

But now, having succeeded,

they have 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 thirty ton adult

It settled here only a few weeks ago

Already, it has attracted hundreds of hagfish

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 along the sides of their bodies

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 hagfish 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,

slowly 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

Eighteen 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 floating

phytoplankton has been transferred from

one link to another in the food chain

and has ended up as far away from the sun

as it is possible to be 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 have 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 around 500 metres

They only come together in these great breeding schools for a few weeks

Just one school was estimated to contain animals that weigh around 4000 tonnes

Wave after wave rise from the depths

and soon the seabed in the shallows is 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

and when the young emerge, they will find more

food more easily than they would in the ocean depths

Dawn the next morning and the seabed for miles around is covered in egg capsules.

The squid themselves have all gone

Many will have died, but some will 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