Original subtitles

Away from all land...

the ocean.

It covers more than half the surface of our planet and yet, for the most part,

it is beyond our reach.

Much of it is virtually empty, a watery desert.

All life that is here is locked in a constant search to find food.

A struggle to conserve precious energy in the open ocean.

The biggest of all fish.

30 tons in weight, 12 metres long,

a whale shark.

Its huge bulk is sustained by near microscopic creatures of the sea,

plankton.

Whale sharks cruise on regular, habitual routes

between the best feeding grounds.

In February, that takes them to the surface waters far from the coast of Venezuela.

Others are already here.

Bait fish have come for the same reason, to feed on the plankton.

The whale shark has timed its arrival exactly right.

Oddly, the tiny fish swarm around it.

They're using it as a shield.

Other predatory fish are lurking nearby.

Yellowfin tuna, they seem wary of the giant.

The shark dives, as if to escape from such overcrowding.

Now the tuna have a chance to attack the unprotected bait fish.

But then back comes the giant!

It has taken a vast mouthful of the bait fish itself.

Plankton, it seems, is not the only food for a whale shark.

Both shark and tuna feast together.

But the tuna must beware.

Even they can end up in the whale shark's stomach.

Predators here must grab what they can, when they can,

for such events do not last long.

The dense shoals on which so many depend gather only when water conditions are perfect.

Many predators spend much of their time cruising the open ocean, endlessly searching.

Plankton-feeding rays do so, gliding with minimum effort.

The Oceanic whitetip shark,

another energy-efficient traveller.

It specialises in locating prey in the emptiest areas of the open ocean,

patrolling the top 100 metres of water.

Taste in water is the equivalent of smell in the air.

An Oceanic whitetip is able to detect even the faintest trace.

Small pilot fish swim with it.

The shark can find prey far more easily than they can

and they'll be able to collect the scraps from its meals.

Its long, fixed pectoral fins enable it to soar through the water

with the least expenditure of energy.

This shark has found a school of rainbow runners.

It would eat one, given the chance.

But rainbow runners are swift and agile and not easily caught.

So, it bides its time.

There's a chance that, eventually, it may spot a weakened fish that's catchable.

The hunter, endlessly waiting.

Excitement far from land.

A school of dolphin, 500 strong!

They've sensed there's food around and they're racing to catch up with it.

The news has spread. Now a number of schools are on their way.

They're heading towards the Azores,

volcanic islands 1, 000 miles west of Portugal.

The dolphins scan the water ahead with their sonar. They're close to their target.

This is it, scad mackerel.

It's difficult for a single dolphin to catch the fish.

To avoid wasting energy, they work as a group.

They drive the fish upwards, trapping them against the surface.

And there, other predators await them.

Cory shearwaters.

They're waiting for the dolphin to drive the prey closer to the surface.

Now the shearwaters can dive down on them, descending to 20 metres or more.

And the dolphins block the bait ball's retreat.

The dolphins leave as soon as they've had their fill.

And, at last, the mackerel sink below the diving range of the birds.

As the sun disappears, a profound change takes place in the ocean.

Deepwater plankton start to rise from the depths

and another hungry army prepares to receive it.

Every night, wherever conditions are right, countless millions of creatures from the deep

migrate to the surface seeking food.

A baby sailfish, 15 centimetres long, snaps up everything in its path.

In three years' time, it will be one of the ocean's most formidable hunters, weighing 60 kilos.

Just now, however, it's very vulnerable.

These manta rays are giants.

Eight metres across and weighing over two tons.

The blade-like projections on either side of the head

help to steer plankton into the manta's mouth.

Dawn returns and the plankton sinks back into the depths.

If we are to follow, we must use a submarine.

As we descend into the darkness, the pressure builds, the temperature falls.

Below 500 metres, new mysterious animals appear.

Their bizarre shapes help them to remain suspended in the dark space.

Some resemble creatures familiar from shallower waters.

Others defy classification.

All around, organic particles drift downwards.

Marine snow, detritus from the creatures swarming in the sunlit waters above.

The snow is food for many animals here,

like the sea spider, a small relative of shrimps and crabs.

Those strange leg-like appendages are feathered to stop it from sinking.

They can also enmesh marine snow, which it wipes carefully into its jaws.

A sawtooth eel hangs upright and motionless.

Gazing ever upwards,

it watches for prey silhouetted against the faint glimmerings of light from the surface.

Days may pass before prey swims close enough for it to strike.

Farther down still, the blackness is complete.

No vestige of sunlight can penetrate as far as this.

Food is very scarce and nothing can afford to waste any energy.

A dumbo octopus simply flaps a fin.

No need for the jet propulsion used by its shallow water relatives above.

The weirdest in this world of the strange,

Vampyroteuthis, the vampire squid from hell.

Disturb it and it only retreats a little distance.

Go after it and it has a special defence.

To see what it does, you must switch off the lights.

The vampire squid has lights of its own.

Bioluminescent bacteria shine from pockets on its arms to confuse its predators.

Are those eyes?

In fact, they're spots at the end of its mantle. A bite there would leave the head unscathed.

The threat diminishes and Vampyroteuthis disappears into the blackness.

At last, the sea floor.

Over two miles down,

the pressure here is 300 times that at the surface.

It takes several months for marine snow to drift down as far as this.

As you travel away from the rocky margins of the continents,

an immense plain stretches ahead.

It extends for thousands of miles, gradually sinking downwards.

There are faint trails in the ooze, signs that even here, there is life.

These are what made some of them.

Sea urchins sifting the accumulating drifts.

Shrimps, standing on elegant tiptoe, fastidiously select the particles that appeal to them.

But in the deep sea, as everywhere else, if there are grazers, there are hunters.

A monkfish, almost indistinguishable from the sand on which it lies.

Why waste energy chasing around if you can attract prey towards you with a lure?

Maybe that one was a bit big.

The monkfish can wait for days, if necessary,

until the right-sized meal turns up.

Scavengers, on the other hand, have to move around to find their food.

Crabs can detect the faintest of tastes in the water and that helps them locate

the latest body to drift down from above.

Eels are already feeding on the corpse.

Isopods, like giant marine woodlice a third of a metre long,

are ripping into the rotting flesh.

Over the next few hours, there'll be frenzied competition

between scavengers of all kinds to grab a share.

Just occasionally, there is a gigantic bonanza.

The remains of a sperm whale.

It died five months or so ago.

There is little left but fatty blubber clinging to its bones.

Its flesh has nourished life for miles around, but now, the feast is almost over.

Spider crabs, a metre across, still pick at the last putrid remains.

A few weeks more and nothing will be left but bare bones.

The crabs will have to fast until the next carcass drifts down.

But not all food comes from the sunlit world above.

The floor of the Atlantic Ocean is split in two by an immense volcanic mountain chain

that winds unbroken for 45, 000 miles around the globe.

In places it's riven by great fissures from which superheated water,

loaded with dissolved minerals, blasts into the icy depths.

Clouds of sulphides solidify into towering chimneys as tall as a three-storey house.

At 400 degrees, this scalding cocktail of chemicals

would be lethally toxic to most forms of life.

But, astoundingly, a particular kind of bacteria thrives here.

And feeding on the bacteria, vast numbers of shrimps.

So, beyond the farthest reach of the sun's power,

a rich independent community exists that draws all its energy

directly from the earth's molten core.

On the other side of the planet, in the western Pacific bordering Japan,

the dragon chimneys.

Another series of hot vents erupting in the darkness.

Here, more, but different, bacteria thrive in a similar way.

And here, too, more crustaceans, but quite different species

from those around the hot vents in the Atlantic.

These are squat lobsters clad in furry armour,

jostling with one another beside the jets of superheated water

for the best places from which to graze on bacteria.

These vents, too, like those in the Atlantic, are isolated oases,

so widely separated, that each community is unique.

Cross to the other side of the Pacific, to the deep near the Galapagos Islands,

and there are yet other fissures venting superheated water.

One and a half miles down, at a site known as Nine North,

towering chimneys support a spectacular display of giant tubeworms.

These vents give off so much energy that some of the worms reach three metres in length.

They're the fastest-growing marine invertebrates known.

All told, over 50 different species have so far been found living here.

The inhabitants of these bustling communities may grow at speed,

but their existence can also be short, for the vents do not erupt indefinitely.

Suddenly, unpredictably, they may become inactive.

Nine months have passed at Nine North.

What were only recently chimneys teeming with life

have turned into cold, sterile, mineral monuments.

Some eddy, deep in the earth's crust, diverted the volcanic energy elsewhere

and an entire micro-world was extinguished.

In places, volcanoes have erupted to build great submarine mountains.

There are thought to be around 30, 000 such volcanoes.

Some measured from the sea floor are taller than Everest.

Sheer cliffs soaring to drowned volcanic peaks.

Powerful currents sweep up the mountain's flanks,

transporting nutrients from deep water towards the summits.

The hard rock provides excellent anchorage

for communities of great variety and stunning colour.

Soft corals, several metres across, collect the marine snow as it drifts past.

Whip corals stretch out into the current.

Giant sponges filter nourishment from the cold water.

A richly varied community flourishes here,

sustained by the nutrients and detritus in the icy currents that flow around the peak.

Yet, it is all blossoming on an extinct volcano a mile below the reach of the sun.

A nautilus. It spends its days hiding 400 metres down,

but as night falls, it ascends up to the reefs to look for food.

Its graceful shell contains gas-filled floatation chambers that control its depth.

It's powered by a jet of water squirting from a siphon.

But it travels shell-first, so it can't see exactly where it's going.

Its nearest living relatives are squid and octopus

which, over evolutionary time, have both lost their shells.

And the octopus has become one of the nautilus's major predators.

It's a master of disguise.

The nautilus keeps well clear of them.

Its small tentacles carry highly-developed chemical sensors

which can detect traces of both predators and prey.

It uses its water jet to dig in the sand.

Because it devotes so little energy to swimming, it only needs a meal once a month.

Got something, and just as well.

Dawn is approaching and it has to puff its way back to deeper waters.

Thirty miles away, shoals of squid are jetting upwards towards the surface.

By night, they seek small fish among the plankton, but they're cautious.

Pacific spotted dolphin.

They're guided by their sonar.

The dolphin, as so often, are working as a team,

synchronising their attacks to confuse their prey.

As dawn approaches,

squid and fish and plankton retreat downwards to shelter in the darkness.

Some of these isolated volcanoes rise as much as 9, 000 metres from the sea floor,

reaching close to the surface.

Around these peaks, invigorated by daily sunshine,

marine life flourishes in spectacular abundance.

Fish crowd here because the volcano forces nutrients to the surface,

encouraging the plankton to bloom.

An oceanic wanderer, a Mola mola,

stops by to be cleaned by reef fish at the seamount edge.

Butterfly fish pluck string-like parasites from its flanks.

The huge fish lives on jellyfish over 1, 000 metres down,

where the water is 20 degrees colder.

So, a brush-up near the surface

allows it to warm up before making more deep-water forays.

The summit of this volcanic mountain rises above the surface of the sea.

It's Ascension Island, 800 miles from any other land.

A welcome, vital haven for long-distance travellers.

Frigate birds spend months continuously airborne at sea,

but at nesting time, they come to Ascension from all over the ocean.

The island's barren slopes of volcanic ash and lava

might seem to offer perfectly good sites for a nest,

but the frigates choose an even more isolated site.

Boatswainbird Island, a lonely pillar just off Ascension's coast.

Frigates are the world's lightest bird relative to their wingspan

and they can soar for weeks on end with minimal effort.

They seem much more at home in the skies than in a crowded colony on land.

But nest they must.

They come from all over the Atlantic to this, their only colony.

There are boobies here, too.

To raise their young, seabirds worldwide seek such remote islands.

Swimmers also come to Ascension to breed.

A female green turtle approaches the coast.

She has not eaten once in two months.

She may have travelled 1, 000 miles from her feeding grounds.

The greatest journey of her kind.

Many others are here, too, resting on the sandy sea floor awaiting the darkness of night

when it will be safer to visit the beaches.

Eggs that were laid a few weeks ago at the start of the season are beginning to hatch.

Most hatchings happen at night.

Now, in the light of day, the young are extremely vulnerable.

They must get to the sea as soon as possible.

But their trials have only just begun.

Many will drown in the pounding waves.

During the next 20 years, the vast majority will inevitably die.

But those that survive will, eventually, as their mothers did before them,

return to the very same beach where they were hatched.

How they find their way back, across thousands of miles of open ocean,

we still have no idea.

A frigate soars.

Somewhere beneath the surface below there is the food it must have.

But where?

Those that fly above the ocean must be able to read the signs of fresh supplies

or perish.

A hundred miles from the Mexican coast and keen eyes have spotted movement.

Sailfish, three metres long, are closing in on prey.

They will only use just enough energy to make their kill,

never wasting a fin stroke.

Nearly a hundred sailfish have surrounded a single school of bait fish.

It's very rare to see so many of these hunters in one place.

To herd their prey, the predators raise their huge dorsal fins.

A mistimed strike by one sailfish could fatally damage another.

But each continually changes its colour from blue, to striped, to black.

That warns its companions of its intentions and also confuses the prey.

As the shoal is driven nearer the surface, it comes within the range of the seabirds.

Out here in the open ocean, there is nowhere for the bait fish to hide.

Sailfish live a high-octane life.

To survive, they must find prey daily.

So their entire existence will be spent on the move.

Over 90% of the living space for life on our planet is in the oceans.

Home to the biggest animal that exists or has ever existed.

The blue whale.

Some weigh nearly 200 tons, twice the size of the largest dinosaur.

Despite their great size,

we still have little idea of where they travel in the vast oceans

and none at all of where they go to breed.

The largest animal on Earth feeds almost exclusively

on one of the smallest, krill, shrimp-like crustaceans.

They take many tons of water into their ballooning throats in a single gulp

and sieve out what it contains.

Every day, each one swallows some four million krill.

Such gargantuan harvests depend on the continuing fertility of the oceans.

But global changes now threaten the great blooms of plankton

on which the whales depend.

Once, and not so long ago,

300,000 blue whales roamed the oceans.

Now, less than 3% of that number remains.

Our planet is still full of wonders.

As we explore them, so we gain not only understanding, but power.

It's not just the future of the whale that today lies in our hands.

It's the survival of the natural world in all parts of the living planet.

We can now destroy or we can cherish.

The choice is ours.