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The oceans, seemingly limitless,

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invoke in us a sense of awe and wonder
and also sometimes fear.

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They cover 70% of the surface
of our planet,

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and yet they are still
the least explored.

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Hidden beneath the waves
right beneath my feet,

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there are creatures
beyond our imagination.

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With revolutionary technology,
we can enter new worlds...

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...and shine a light on behaviours

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in ways that were impossible
Just a generation ago.

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We've also recognised
an uncomfortable fact.

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The health of our oceans
is under threat.

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They're changing at a faster rate
than ever before in human history.

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Never has there been a more crucial time

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to reveal what is going on
beneath the surface of the seas.

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In this first episode,

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we will journey across the globe
from the warm waters of the tropics

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to the coldest around the poles.

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To bring us a new understanding
of live beneath the waves.

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This is Blue Planet II.

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The surface of the ocean conceals
the many creatures that live beneath

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but not all.

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Bottlenose dolphins.

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They're extremely intelligent.

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And with this intelligence
comes playfulness.

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They surf.

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And as far as we can tell,
they do so for the sheer joy of it.

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But to properly appreciate
their true character,

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you have to travel with them
into their world.

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A pod of bottlenose dolphins is visiting
a coral reef in the Red Sea.

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For the youngsters,
there are things to be learned here.

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The adults lead a calf
to a particular bush-like coral

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called a Gorgonian.

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And here, the adults behave
rather strangely.

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They deliberately rub themselves
through the fronds.

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Their calf seems reluctant to do so.

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By watching his elders,

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he may be realising
that this is something he ought to do.

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Gorgonia fronds, in fact,
are covered with a mucous

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that can have anti-inflammatory
and antimicrobial properties.

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So maybe the adult dolphins
are doing this

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to protect themselves from infection.

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The dolphins' intimate knowledge
of the reef

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is spurring us to search
for new medicines here, too.

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Tropical coral reefs

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occupy only a tenth of one percent
of the ocean floor.

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But their shallow warm waters
and stable year round conditions,

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support some of the most crowded
and varied communities

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to be found anywhere in the oceans.

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And there are new discoveries to be made
on every one of them.

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One creature
on Australia's Great Barrier Reef

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is challenging our understanding
offish intelligence.

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A tusk fish.

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And you can see why it gets its name.

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He does something
few would have believed a fish could do.

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Every morning,
he travels to the edge of the reef

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He's searching
for something special to eat

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amongst the coral and sand.

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Here's one.

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A small clam.

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But how to crack it open
and get to the meat?

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He takes it all the way back

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to his special kitchen.

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A bowl-shaped coral

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that has a particular bump on the inside
that he always uses.

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It's not easy if you have no hands.

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Whoops.

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There he goes again.

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But he's got great determination

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and surprising accuracy.

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At last.

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So here is a fish that uses tools.

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Some fish are much cleverer
than you might suppose.

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The density of the animals
on tropical reefs

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makes competition
inevitable and extreme.

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Not only for those that lived
within the reef,

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but for the birds that fly above them.

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During the dry season,

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over half a million terns

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crowd onto this remote atoll
in the Indian Ocean.

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Their chicks are still
in their dark, Juvenile plumage.

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They vary in age.

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Whilst the more advanced chicks
take to the air,

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others aren't quite ready yet.

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Those just starting to learn to fly

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use the shallow lagoon
that occupies the centre of the atoll

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as their training ground.

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It's difficult for some of them
to stay aloft for long.

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Giant trevallies.

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Usually, they're solitary hunters,

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but about 50 of them have come here
from neighbouring reefs

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attracted by this abundance
of potential prey.

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The fledglings stay out of the water
if they can,

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they even drink on the wing.

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If the trevally are to catch one now,

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they have to up their game.

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So there is a fish here that amazingly

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has a brain capable of calculating
the airspeed,

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altitude and trajectory of a bird.

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The time comes when every fledgling
has to take to the air

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and collect food for itself

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Their parents lead them
to the training grounds.

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If they're to survive,

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they must learn quickly.

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After a month of practising
over the lagoon,

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the youngsters start to leave

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and take their chances
out over the open sea.

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The oceans hold 97% of all the water
in the world.

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As the sun warms their surface,
water evaporates.

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The vapour rises into the sky

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until it cools and condenses
into towering clouds.

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And they generate huge storms.

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The spin of the earth
deflects these storms

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north and south into cooler latitudes.

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As they travel across the sea,

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storm-driven winds create huge swells.

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When the swells reach shallower waters,

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they rise into gigantic waves.

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In its lifetime,
a large storm can release energy

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that is the equivalent
of 10,000 nuclear bombs.

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These are the seasonal seas.

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And when they warm in spring,

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they can suddenly explode with life.

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Mobula rays have gathered
in Mexico's Sea of Cortez

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in vast numbers.

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Why do they leap?

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Is it to tell others that they're here?

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No one knows.

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They feed mostly at night

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for that is when vast swarms
of plankton rise from the depths.

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The disturbance in the water stimulates
many of the planktonic creatures

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to luminesce.

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Only now do we have the technology
to record their faint glow.

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The feasting rays swim through them

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creating an extraordinary ballet
of life and death.

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The richness of these waters
is based on microscopic plants,

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phytoplankton,

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which bloom on such a massive scale
they benefit us all.

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They, together with seaweeds
and seagrasses,

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produce as much oxygen

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as all the forests
and grassy plains on land.

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Every spring off New Zealand,

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the seasonal bounty
draws in rare visitors.

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False killer whales.

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They're relatives of the orca,

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six metres long
and weighing over a tonne.

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They appear to be searching
for dolphins.

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And there are many
in these coastal waters.

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Here, bottlenose dolphins stick together

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constantly chattering
with whistles and clicks.

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Such a din carries for miles underwater.

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The false killers have detected them.

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Travelling at ten knots,
the killers quickly close in on them.

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But then,
something truly extraordinary happens.

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The dolphins turn

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as if to greet their pursuers.

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They seem to change their course.

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00:27:19,931 --> 00:27:23,392
Could it be that they're attempting
to communicate?

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Scientists studying
this annual encounter,

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now think that individuals
may recognise one another.

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Almost unbelievably,
it seems that these different species

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appear to be old friends.

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Together they're gathering
as one unified army

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up to a thousand strong.

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This formidable hunting party
now harvests the riches

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that come with New Zealand's summer.

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All across the higher latitudes,

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seasonal seas flourish
under the summer sun.

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Here in Alaska,
sea otters lounge in the canopy

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of great submarine forests.

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Giant kelp, the biggest seaweed of all
is home to all kinds of life.

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On the forest floor, spiny
sea urchins munch through the kelp.

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Elsewhere there are continuously hungry
sea cucumbers

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And in the tangled undergrowth,

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wonderfully camouflaged sea dragons.

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In the underwater forests
of northern Japan,

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the residents of this sunken wreck

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are waiting for the summer temperatures
to reach 16 degrees Celsius.

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That for some is the time for mating.

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A kind of giant wrasse called a Kobudai.

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This is a male.

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And in female terms,
he's particularly handsome.

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He's a metre long and weighs 15 kilos.

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Much larger than the diminutive female,

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and he is ready to breed.

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He attempts to mate with her

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and with any of the dozen or so females
that live in his territory,

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whenever he gets the chance.

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But females from around ten years old

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take little notice of his advances.

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This is because when any large female
reaches a critical body size,

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she can begin a dramatic transformation.

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Over just a few months,

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particular enzymes inside her body
cease to work,

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and male hormones start to circulate.

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As time passes,

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her head expands

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00:33:09,905 --> 00:33:11,907
and her chin gets longer.

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A she has changed into a he.

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00:33:28,966 --> 00:33:32,011
And with this comes a change
in temperament.

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The old male who rules
all the females here

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is challenged to a face off

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The more bulbous the head,

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the more it intimidates an opponent.

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The territory has a new ruler.

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00:34:42,831 --> 00:34:47,211
Only the largest females transform
themselves in this way.

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00:34:53,092 --> 00:34:56,595
But the change enables them
to have more mates,

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00:34:56,929 --> 00:35:01,058
so they will have many more offspring
carrying their genes.

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00:35:07,356 --> 00:35:10,025
But a new male can't afford
to be complacent.

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00:35:12,861 --> 00:35:16,365
Inside the body of every Kobudai female,

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there is a new male in waiting.

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00:35:40,472 --> 00:35:45,561
The closer we travel towards the poles,
the colder the seas become.

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00:35:49,315 --> 00:35:50,899
Icebergs appear.

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00:35:51,066 --> 00:35:53,819
Huge slabs that have broken away

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00:35:53,902 --> 00:35:56,071
from glaciers that are sliding
into the sea.

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00:35:57,906 --> 00:36:01,618
And then the surface starts to freeze.

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00:36:12,296 --> 00:36:15,591
While the lights of the aurora
play above,

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00:36:15,799 --> 00:36:17,760
even in the depths of midwinter,

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00:36:18,344 --> 00:36:22,014
there are a few places
well north of the Arctic circle

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00:36:22,139 --> 00:36:23,640
that are still open.

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The fjords of northern Norway
remain ice free

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00:36:39,156 --> 00:36:42,159
because a giant current,
the Gulf Stream,

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00:36:42,284 --> 00:36:44,203
flows up here from the south

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00:36:44,286 --> 00:36:47,539
bringing warmth all the way
from the Caribbean.

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00:36:51,627 --> 00:36:53,128
And every winter,

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00:36:53,212 --> 00:36:56,715
billions of herring
come here for shelter.

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00:37:00,886 --> 00:37:02,596
And following them...

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00:37:05,307 --> 00:37:06,517
...Orca.

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00:37:19,029 --> 00:37:21,490
There are up to a thousand of them.

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00:37:23,325 --> 00:37:27,704
It's possibly the greatest gathering
of orca on the planet.

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00:37:38,006 --> 00:37:42,302
The herring maybe plentiful
but in these winding fjords

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00:37:42,386 --> 00:37:45,264
they're not always easy to track down.

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00:37:49,852 --> 00:37:52,229
These particular orca, however,

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00:37:52,688 --> 00:37:55,190
are fish hunting specialists.

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00:38:04,616 --> 00:38:05,909
They work as a team,

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00:38:06,034 --> 00:38:10,706
coordinating their approach
by calling loudly to one another.

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00:38:16,044 --> 00:38:19,798
They herd the herring
into tighter and tighter shoals.

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They swim below them,

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trapping them against
the surface of the sea.

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00:38:48,911 --> 00:38:52,831
And now the orca deploy
their special weapon.

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00:38:58,337 --> 00:39:01,423
They beat their tails with such force,

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00:39:01,590 --> 00:39:04,468
that the shock waves stun the herring.

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00:39:07,262 --> 00:39:11,517
And then the senseless victims
are easily collected.

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00:39:46,969 --> 00:39:50,973
But all this underwater noise
attracts others.

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00:39:59,147 --> 00:40:00,983
Humpback whales.

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They move in on the action.

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00:40:13,829 --> 00:40:18,000
They approach the shoal from beneath
and then lunge upwards,

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00:40:24,590 --> 00:40:29,177
gathering up to a hundred kilos
of herring in a single mouthful.

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00:40:48,697 --> 00:40:51,742
The humpbacks are comparative newcomers.

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00:40:52,701 --> 00:40:56,204
They only started coming here
within the last decade.

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00:41:07,716 --> 00:41:10,761
But these polars seas are so rich

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00:41:10,886 --> 00:41:13,805
that there appears to be enough food
for everyone.

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00:41:36,995 --> 00:41:40,415
Nonetheless, few if any of these riches

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would be here were it not
for the Gulf Stream.

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00:41:53,595 --> 00:41:58,433
Ocean currents, in fact, are crucial
to the well being of our planet.

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00:42:03,605 --> 00:42:06,858
They distribute the sun's heat
towards the poles

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00:42:06,942 --> 00:42:08,610
all the way from the equator,

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00:42:11,279 --> 00:42:15,826
maintaining a climate favourable
for life almost everywhere.

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00:42:22,624 --> 00:42:25,961
From creating the weather
to producing oxygen,

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00:42:26,044 --> 00:42:28,964
the seas keep our world healthy.

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00:42:38,515 --> 00:42:41,059
But there are now worrying signs

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00:42:41,184 --> 00:42:42,811
that conditions in the oceans

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00:42:42,894 --> 00:42:45,814
that have remained relatively stable
for millennia

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are changing radically.

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00:42:50,068 --> 00:42:53,739
Nowhere is this more evident
than in the Arctic.

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00:42:56,074 --> 00:42:58,160
Here in the past 30 years,

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00:42:58,243 --> 00:43:03,039
the extent of the ice in summer
has been reduced by 40%.

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00:43:04,207 --> 00:43:06,001
This sudden warming,

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00:43:06,168 --> 00:43:09,087
most likely a consequence
of human activity,

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is having a profound impact
on its wildlife.

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00:43:20,557 --> 00:43:24,644
Walruses are among those
that are seriously affected.

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Every adult female
needs to find a safe place

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00:43:38,909 --> 00:43:41,703
where her 80-kilo pup can rest.

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The sea ice is retreating

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00:43:46,458 --> 00:43:49,211
from much
of the walrus' traditional range,

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00:43:49,419 --> 00:43:52,714
so they now have
to haul out on dry land.

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00:43:58,261 --> 00:44:01,848
But a herd of hundreds
of quarrelsome mothers,

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some weighing almost a tonne,
is not an ideal nursery.

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Walruses on land stick together
for good reason.

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Polar bears.

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00:44:27,999 --> 00:44:31,378
A full grown male walrus is gigantic,

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00:44:31,461 --> 00:44:34,339
too big for even a polar bear to tackle.

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00:44:36,424 --> 00:44:39,928
So the bear is looking
for a walrus baby.

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00:44:46,268 --> 00:44:49,688
The scent of the bear
spreads alarm through the colony.

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00:44:57,445 --> 00:44:59,865
The walruses retreat into the sea.

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00:45:18,800 --> 00:45:22,304
The bear knows it won't be able
to catch them there.

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00:45:32,564 --> 00:45:35,483
But she too has young ones to feed.

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00:45:43,158 --> 00:45:46,161
What is a mother to do?

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00:45:56,588 --> 00:45:59,549
A mother walrus still needs
to find a place

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00:45:59,674 --> 00:46:01,343
where her young can rest.

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00:46:09,351 --> 00:46:11,686
A melting iceberg might do,

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00:46:13,063 --> 00:46:16,358
but she is not the first
to find this one.

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00:46:24,199 --> 00:46:27,202
Suitable places are already taken.

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00:47:01,903 --> 00:47:04,614
Other mothers don't want to share.

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00:47:09,619 --> 00:47:13,248
They, too, need a patch of ice
where they can protect their young.

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00:47:19,754 --> 00:47:24,634
A desperate mother has no choice
but to barge her way in.

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00:47:48,867 --> 00:47:51,786
So this time everyone loses.

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00:48:18,146 --> 00:48:21,316
Finding the right place
on these melting shores

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00:48:21,524 --> 00:48:24,402
gets harder and harder.

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00:49:00,522 --> 00:49:06,486
Solving these problems together
helps create a bond so strong

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00:49:06,569 --> 00:49:11,449
that the mother will stay in contact
with her young for the rest of her life.

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00:49:23,545 --> 00:49:27,298
But who knows now
what their future will be.

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00:49:41,729 --> 00:49:45,150
As we understand more
about the complexity

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00:49:45,316 --> 00:49:47,735
of the lives of sea creatures,

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00:49:49,112 --> 00:49:53,408
so we begin to appreciate
the fragility of their home.

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Our blue planet.

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Next time.

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The deep.

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00:50:18,183 --> 00:50:21,269
A world richer
than we ever though possible,

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00:50:22,687 --> 00:50:24,189
where creatures thrive,

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00:50:26,024 --> 00:50:29,611
in the most extreme conditions on Earth.