Original subtitles

The world's greatest wilderness, the open ocean.

It covers over half the surface of our planet.

Here, there is nowhere to hide and little to eat.

It's the marine equivalent of a desert.

And patrolling this desert, spinner dolphins.

They stick together.

In a super pod, 5,000 strong.

That maximizes their chances of finding something to eat.

Like all who live here, they must go to extraordinary

lengths to make their home in the Big Blue.

There are rare moments when these empty seas can explode with life.

Lanternfish off the Pacific coast of Costa Rica. They're

scarcely bigger than minnows, but what they lack in size,

they make up for in numbers.

They are one of the most numerous fish anywhere.

Normally, they only come to the surface at night to feed on

plankton. But this immense shoal has risen during the day,

almost certainly in order to spawn.

For the dolphins, this would be a balancer.

They have located the shoal using their echo sounding calls.

But they have to get to it quickly.

They are not the only hunters here.

Yellowfin tuna have also detected the shoal.

And behind them, with their two-meter wingspans, mobula rays.

Now, sailfish, one of the fastest fish in the sea, have joined the chase.

The lanternfish may return to the deep at any moment.

But now, the dolphins have got here.

They swim beneath the shoal, pinning it to the surface

and forcing the lanternfish to pack more closely together.

And now, the sea begins to boil.

The tuna charge into the shoal at over 40 miles an hour.

The slower swimming rays arrive at last.

With their immense mouths agape, they scoop up the lanternfish by the hundred.

The shoal has now been largely dispersed, and the sailfish

pick off the survivors. In just 15 minutes, all that's left

is a silvery confetti of scales.

But here, such feasts are only too infrequent.

Whilst the dolphins perform great feats of endurance, others

are driven to even greater extremes to find food in this

ocean desert.

A sleeping giant.

A sperm whale.

This family is resting between bouts of feeding.

Who knows what the owners of the biggest brain in the planet dream about?

One has a calf. It's about two weeks old, but

still dependent on its mother's milk. It's hungry.

It communicates with its mother using a pattern of clicks.

But its mother slumbers on.

The calf, covered in suckerfish, of which it can't yet rid itself, has to be patient.

Sleep over and refreshed. The whales move on.

Sperm whales don't wait for their prey to rise to the

surface. They swim down into the depths to find it.

They take a series of heavy breaths to

saturate their blood with oxygen. Then, down they go.

This entire family dives together in search of squid.

A mother will push her body to the limits of her endurance,

and already it's hard for her calf to keep up with her.

The calf sticks to its mother as closely as it can, touching her frequently,

as if for reassurance.

About 300 meters down, it seems the calf can't hold its breath any longer.

In their early years, calves are forced to sit out the hunt.

The adults continue their dive.

The mother changes her calls into a series of louder and more rapid clicks.

She's now using sonar to hunt down shoals of squid.

At 800 meters, a burst of clicks.

Then silence.

She's made a catch.

The hunters could be away for as much as an hour.

Finally, the mother returns from the deep with a stomach full of squid.

After a long wait, this hungry calf can take some milk.

It's one of the richest produced by any mammal,

and the calf guzzles a bathful of it a day.

It may be six years before a calf masters the art

of deep diving and is able to find food for itself.

The emptiness of the Big Blue is what makes life so hard for hunters.

But it's this emptiness that makes it comparatively safe for prey.

A baby turtle, hatched just days ago, is leaving the

crowded, dangerous waters of the coast and heading for the

open ocean.

Only recently have we begun to solve the mystery of

where baby turtles disappear to in their early years.

To start with, they fill their little stomachs with

plankton, but soon they need something more substantial.

Hundreds of miles offshore, in every ocean, there are communities of young castaways.

So, anything that floats attracts them.

A log. It may have been at sea for several years, and it

has already become the center of a small community. Young

pufferfish are here for the same reason.

A floating log is just the kind of refuge this young turtle

has been looking for. Here, there's not only seaweed on

which to graze, but barnacles.

But it's important to stay undercover.

A young, ocean-going, silky shark is here too.

It's learning what tastes good, and

what doesn't.

We now know that many young turtles stay in

such places for several years, until adulthood.

Even if it means facing the full force of the high seas.

The sun, beating down on the deep blue, warms

the surface waters so that they evaporate.

As the vapor rises, it condenses into clouds. They rapidly

build into gigantic, burgeoning towers, which eventually

generate violent storms some a thousand miles across. High -enforced

winds sweep across the open ocean, building waves that can rise to 30 meters tall.

Out here, ships have been known to sink without trace.

130 million containers are shipped across the oceans every

year, and on average, four of them fall into the sea every

day.

In 1992, a few were lost that contained a consignment of bath toys,

including 7,000 plastic ducks like these.

They started their travels a thousand miles off Alaska.

Some drifted right across the Pacific Ocean and reached Australia.

Others were carried north and landed on shores between

Russia and Alaska. They even found their way into the high

Arctic.

One duck, having been at sea for 15 years and crossing three

oceans, eventually landed on the west coast of Scotland.

Their travels vividly illustrate how a network of currents

connects all our oceans into one gigantic circulatory

system.

Many of the inhabitants of the Big Blue rely on

these currents to carry them to feeding grounds.

The Blue Shark.

It travels over 5,000 miles a year, riding on the

currents supported by its broad wing-shaped fins.

This one may not have eaten for two months.

But the currents can carry promising traces of fatty oils

from many miles away and will lead it to its next meal.

After days of travel, the smell of food gets stronger.

A dead whale recently struck by a ship.

This could be a real feast, but the Blue Shark must be cautious.

Great White Sharks,

ten times heavier than a Blue, are highly possessive around a whale

carcass. Great Whites

are eager to feed on energy-rich whale blubber,

which we now know forms a major part of their diet.

Once the Great White has had its fill, smaller sharks,

like the Blue Shark, tackle what's left of a carcass.

As the oils from this dead whale spread more

widely, more and more Blue Sharks appear.

Within days, the carcass will be stripped of its blubber.

Then, no longer kept buoyant by its oil, it will sink into the depths below.

The Blue, with its reserves of fat replenished, can

now survive for another two months without eating.

Over half of all animals in the open ocean drift in currents.

Jellyfish cross entire oceans, feeding on

whatever happens to tangle with their tentacles.

Some can go to a meter, even two meters across. And when,

by lucky chance, they encounter a patch of sea rich in

plankton, their numbers

It's such a successful strategy that jellies

are one of the most common life forms on the

But among the jellies, and looking somewhat like

them, is a rather more complex and sinister creature.

The Portuguese Man O' War.

It floats with the help of a gas-filled bladder, topped by a

vertical membrane. With that serving as a sail, it maintains

a steady course through the waves.

Long threads trail behind it, some as much as 30 meters long.

Each is armed with many thousands of stinging cells. A

single tentacle could kill a fish, or, in rare cases, a

human.

But among its lethal tentacles lurks a Man O' War fish that feeds by nibbling them.

Whilst this fish has some resistance to the stings, it must still be extremely careful.

Most other fish are not so lucky.

A tentacle has caught this one and reels it in.

It's already paralysed.

Specialized muscular tentacles transfer the victim to

others that digest the catch, liquefying it with powerful

chemicals.

Eventually, all that is left is

a scaly husk.

This voracious Man O' War may collect over a hundred small fish in a day.

For the most part, the Big Blue seems featureless,

a place where the winds blow uninterrupted by land.

But beneath the surface, there are long mountain ranges,

deep trenches, and isolated volcanic peaks that make it far

more varied than the human eye can see.

We're only just discovering, in any detail, how

the inhabitants of the Big Blue exploit that.

A lonely whale shark on a special journey.

She is as long as a small aircraft and she weighs over 20 tons.

Like many sharks, she does not lay eggs, but gives birth to live young.

She carries up to 300 of them in her swollen belly.

She may be the biggest fish in the sea, but the place

where whale sharks give birth has not yet been found.

Today, however, we may be a step closer to solving this

mystery. We have known that great numbers of whale sharks at

certain times of the year appear around the Galapagos

Islands. Here they assemble around a tiny island that rises

abruptly from particularly deep water.

It's known as Darwin Island.

Here, swirling currents bring up nutrients from the

deep, so enriching these waters that they attract great

concentrations of fish from far and wide.

Thousands of hammerhead sharks also assemble here. They are nearly all female.

They too, it seems, have come here to breed.

The whale shark receives an extraordinary welcome.

Silky sharks, themselves three meters long, bounce against the rough skin.

Perhaps to scrape off any parasites they might have.

These sharks could be a danger to any newly born young.

So perhaps to avoid them, the whale shark dives.

Down to around 600 meters.

And there she may release her young. In these great depths,

away from the predators that hunt in the waters above, and

with abundant food, her babies could grow and eventually disperse.

No one, it is true, has ever seen young ones in these little visited depths.

But the fact that hundreds of expectant whale sharks come

here every year is strong evidence that somewhere here lies

the nursery of the biggest fish in the sea.

There are almost 30,000 sizable islands, scattered across the world's oceans.

One of them is South Georgia.

An ideal place for those ocean dwellers who are compelled to land in order to breed.

The wandering albatross.

It may spend as much as a year continuously at sea.

Searching for food, gliding on wings that are three and

a half meters across, the biggest of any living bird.

The entire world population of 16,000 wanderers nest on

South Georgia and half a dozen or so of the other smaller

islands that lie in the Southern Ocean.

It's spring, and this bird is returning to the nest site it's always used.

Its lifelong partner is already here.

In South Georgia, individual birds have been studied for

their entire lives, revealing that older pairs in their late

30s will go to extraordinary lengths to give

their young the best possible start in life.

This chick is now several weeks old, but still has its warm downy coat.

The chick will need a regular supply of regurgitated fish and squid.

With food so scarce in the open ocean, both parents may have

to scour thousands of square miles just to provide enough

for one meal.

Aging parents struggle on all through the Antarctic

winter to raise a chick that is big, strong and healthy.

After some 130 days, the youngster begins to replace its down with flight feathers.

Finally, nine months after their egg was laid, this chick is ready to leave.

Of all the chicks they've reared in recent years, such a

favored chick will have the best chance of survival, but it

will also be their last.

Elderly parents never recover from their exertions.

Surviving in the open ocean has always tested animals to

the limit. But today they face a new additional threat.

Plastic.

Just over 100 years ago, we invented a wonderful new

material that could be molded into all kinds of shapes, and

we took great trouble to ensure that it was

hard-wearing, rot-proof and virtually indestructible.

Now, every year, we dump around 8 million tons of it into

the sea. Here, it entangles and drowns vast numbers of

marine creatures.

But it has even more widespread and far-reaching consequences.

A pod of short-finned pilot whales.

They live together in what are perhaps the most

closely knit of families in the whole ocean.

Today, in the Atlantic waters of Europe, as

elsewhere, they have to share the ocean with plastic.

A mother is holding her newborn young.

She is reluctant to let it go and has been carrying it around for many days.

As plastic breaks down, it combines with other pollutants

that are consumed by vast numbers of marine creatures.

In top predators like these, the toxic chemicals can build up to lethal levels.

It's possible her calf may have been poisoned by her own contaminated milk.

Pilot whales have big brains. They can certainly experience emotions.

Judging from the behavior of the adults, the loss

of the infant has affected the entire family.

Unless the flow of plastics into the world's oceans is

reduced, marine life will be poisoned by them for many

centuries to come.

The creatures that live in the Big Blue are perhaps

more remote than any animals on the planet, but

not remote enough, it seems, to escape the

effects of what we are doing to their world.

The biggest challenge of filming in the vastness

of the open ocean is to find your subject.

And the Blue Planet team wanted to film one of the most

elusive of them all, the rarely witnessed boiling sea.

Until now, this feeding frenzy has been the stuff of legends.

After some promising sightings off the northeast

coast of Australia, the team heads out to investigate.

We know it's a phenomenon, we know it's out there, the

scientists have documented it, the fishermen have told us

about it, so we know it's happening, but no one has been

crazy enough to attempt to go out there and actually film it

except for us. The team start their search a hundred miles out in the Pacific Ocean.

The reason it's called the boiling sea is that the tuna are

actually coming out of the water and attacking Atlantic fish

and it creates a lot of white water.

To film the boiling seas, the team must first find a large

shoal of bait fish, most likely to be lantern fish rising to

the surface at night to spawn. A few days out, Adrian thinks

he may have spotted a giant shoal on the echo sounder. What

we're seeing is a very, very dense layer at about 200

metres water depth and so the fact that we've got this would

suggest that we have a very deep and dense layer of fish.

One of the best ways to film at such depths in the open

ocean is to use an ROV, a remotely operated vehicle, carrying a light-sensitive camera.

But working with such heavy equipment in the high seas is a risky operation.

Fortunately, a team of technicians is on hand

and 24 hours later they're ready to relaunch.

Adrian drops them on top of what he hopes is a large shoal

of lantern fish. Good news is we've just put the ROV down,

we're down at 250 metres, which means we've gone to almost

the end of the cable and nothing's blown up, so we're back

in business. But there's almost nothing there, just a thick layer of plankton.

Over the next three weeks they don't find a single lantern fish.

This trip is the perfect illustration of why we know so much

about the ocean. We came out looking for something, we've

searched and searched and searched and we still haven't

found it, even with every single tool you could wish for. As

it turned out, the team had been filming at the very

start of El Niño, an unpredictable climatic event when sea

temperatures can suddenly rise and disrupt the spawning behaviour of fish.

It would be 18 months before conditions would

improve and the team could continue their quest.

The other side of the Pacific Ocean, off Costa Rica.

This time, rather than searching for their

prey, the team are looking for their predators.

But in the endless blue, even finding a massive pod of dolphins isn't easy.

20 miles offshore, series producer Mark Brownlow leads an

aerial filming team, scanning thousands of square miles of

ocean.

But there's not a dolphin in sight.

Day three, no spinner dolphins.

Finally,

after 10 days on the open ocean, they get their reward.

With dolphins in sight, the dive team race to intercept them. The plan is

to film the dolphins feeding frenzy from underwater.

They catch up with the dolphins.

But they're too late.

To stand the

chance of filming the dolphins feeding, the dive team need to be more proactive.

Rachel hitches a ride, following them underwater,

searching for any clue to where they might go next.

Finally, after three weeks of searching, the dive team catch

a huge feeding event. A massive shoal of lanternfish being

rounded up by hundreds of spinner dolphins.

For the first time, the aerial team can record the epic scale of this spectacle.

The vastness of

the ocean wilderness made capturing this extraordinary event a great challenge.

But this is the reward, a moment of unparalleled

drama in the immense expanse of the Big Blue.

Next time, we journey into the bountiful Green Sea.

These are enchanted worlds home to strange creatures, where

only the most ingenious will live.

Thanks for watching.

See you next time.