All language subtitles for The.Blue.Planet.S01E05.Seasonal.Seas.1080p.AMZN.WEB-DL.DD+2.0.H.264-playWEB_track3_[eng]

There are some seas

where fish swarm
in millions,

and plankton blossoms
in vast clouds.

The sheer quantity
of life here

is unmatched anywhere
in the oceans.

These are the most
productive seas on Earth.

They are
the seasonal seas.

The seasonal seas border

the temperate parts
of the world,

where conditions change
through the year.

The seasons also affect
the underwater world.

The power of the sun
is constantly changing.

In the far north,
during the summer,

there are long hours
of sunlight.

But in winter,
that dwindles,

and eventually,
there can be weeks of darkness.

The summers
are warm and gentle,

the winters racked
by savage storms.

In conditions
like this,

life of any sort
has to struggle to survive.

January on Sable Island,

off the coast of Nova Scotia
in North America.

Grey seals have managed
to get ashore

through the
crashing breakers.

Gales here can blow
for days on end.

Sable Island has the world's
largest colony of grey seals.

100,000 come here
to breed each year,

just when the weather
is at its worst.

To add insult to injury,
the pups,

having suckled for only 18 days,
are then abandoned.

Their mothers must
return to the sea

to find food
for themselves.

As yet unable to dive,
the pups are marooned,

and sustained by nothing
except their fatty blubber.

It will be five weeks before
they are strong enough to swim.

But by then,
it will be early spring,

and the ocean will be
teeming with food.

By May, spring has reached
the coasts of Scotland.

Underwater,
it arrived rather earlier.

During March,
the seas had warmed enough

to trigger
a magical transformation.

These are phytoplankton--
tiny, floating algae,

each much smaller
than a pinhead.

And they multiply
with amazing speed

to produce
more annual growth

than all the plants on land
put together--

6 billion tons of it.

This immense bloom spreads
across the face of the ocean,

and within
a couple of months,

turns vast areas of it
a dense green.

Let's begin.

My dog is one of us.

You and me, girl.

Home protection?
Hunting.

Out here,
most folks let things go.

I guess I'm not
most folks.

I want to live.

Are you prepared to kill?

Yes.

One of us is not
leaving this island.

You ready?

Animal life reacts
to the blooming sea.

Although these polyps
look like small anemones,

they're about to change
into something else.

As they separate,

they reveal themselves
to be tiny common jellyfish.

They're less than
3 millimeters across.

Within a few months,

they will have assembled
into vast swarms.

Minute copepods are
part of their staple diet.

These appear every spring,
in vast numbers,

and graze on
the phytoplankton bloom.

Their beating legs
create currents

that sweep
the little algae

into the basket-like filters
around their mouths.

On this microscopic scale,

water is so viscous
that the phytoplankton

can't swim against
the current.

Whilst feeding, sensors on
the copepod's antennae

give warning
of dangers ahead.

Lighting by lasers
reveals that feeding copepods

leave wakes behind them, rather
like jet trails in the sky.

Slightly larger
floating predators

are able to use these trails
to find their prey.

A close call,

but some predators are simply
too large to avoid.

Jellyfish.

They may appear to be delicate
as well as beautiful,

but they are
deadly hunters.

With every pulse
of the delicate bells,

plankton-rich water is
drawn into their lacy throats

and pushed out again,

leaving behind copepods
stuck to the membranes.

A single sea nettle jellyfish,
only a few centimeters across,

can collect thousands
of copepods in a day.

So the killing power
of giants, like these,

is hard to estimate.

Each of these jellyfish
weighs up to 30 kilos,

and has tentacles
stretching over 8 meters.

But there are even greater
dangers awaiting the copepods.

By the late spring,

the baby common jellyfish
are fully grown.

They gather in millions,
forming immense swarms

hundreds of meters long,
which filter out

all the small planktonic animals
in their path.

Nevertheless, there are such
astronomic numbers of copepods

that enough will survive
to form swarms of their own.

A basking shark.

This huge 8-ton fish
feeds on plankton,

and nothing else.

Every hour,
it filters 1,000 tons

of seawater
through its gills.

Numbers of these shark appear
when the bloom is at its peak,

and travel along
those water currents

where the plankton
is thickest.

Even so, the supply of plankton
is so abundant

that another group of animals
is able to share in the feast--

animals that live
on the seafloor.

Every centimeter of rock

is covered with invertebrates
of some kind--

anemones, sea squirts,
gorgonians--

all trapping plankton
from the passing water.

Not all life in the seasonal
seas depends upon the plankton.

It's early spring
in British Columbia.

Seaweed has started to grow
slowly in the cold water.

As the hours
of sunlight increase,

and the water warms,

these small plants turn into
great beds of bull kelp.

The immense,
30-meter-long strands

have small,
gas-filled floats

which keep them
high in the water,

within reach of
the energy-giving sunlight.

Further south,
the sunshine is more powerful,

so here, on the coast
of California,

the biggest kelp of all
can grow.

This is giant kelp,
and by midsummer,

each plant is growing in length
by nearly a meter a day.

The main stem is fixed to
the bottom 35 meters below

by a small,
but immensely strong, holdfast.

Fully grown, these gigantic
plants are 100 meters long,

and they form
vast marine forests.

Great schools of fish
find sanctuary here.

These are
blacksmith fish.

They are plankton feeders,
and whenever it seems safe,

they head off
into open water

to feed where the plankton
is thickest.

But at the first hint
of danger,

they rush back to
the safety of the forest.

Fish are not the only creatures
that shelter here.

Californian sea otters
gather in the kelp forest

to rest and snooze
in safety.

To prevent themselves
being carried away

into dangerous open water,
where the big predators cruise,

they anchor themselves

by winding straps of kelp
around their body.

Sooner or later,
they have to find food,

and that lies on the seabed
a long way below them.

Sea otters, however,

can stay underwater
for up to 10 minutes,

and that's ample time to find
the shellfish they need.

Many of the smaller creatures
that live in these forests,

such as urchins,
graze on the kelp,

and can seriously damage it
if their numbers are unchecked.

The sea otters, however,
feed on some of these grazers,

and prevent them
getting too numerous.

So, in effect,
the sea otters

are the guardians
of the forest.

Garibaldi fish do not,
in fact, damage the kelp.

If anything, they help it
by picking off tiny animals

that, in places,
encrust the leaves.

They graze on bryozoans,

tiny colonial animals
which build their colonies

like a patchwork of white skins
on the leaves.

When night falls, there are
fewer predatory fish around,

and the bryozoans emerge
from their white shelters.

Now, just like
coral polyps,

they start filtering out
the plankton

under cover
of darkness.

They're not the only animals
to venture out at this time.

This is an amphipod,
2 two centimeters long,

and it does eat kelp.

In turn, it is excellent food
for many predators.

To protect itself, it produces
silk, just like a spider,

and uses it to sew together
two sides of a kelp frond,

and so,
form a shelter.

This one is in particular need
of a secure home.

She's a mother.

There are over 50 youngsters
clustered on her abdomen,

so her home is becoming
somewhat cramped.

They will soon be
old enough to leave,

and now,
whenever she can,

she kicks them out, to get
a taste of the outside world.

Dawn.

Beds of eelgrass
grow in the shallows

between the kelp forest
and the shore.

A harbor seal
has found sanctuary here,

and is sleeping after
a hard night's foraging.

But not for long.

A male seal
gives a wake-up call.

More seals are attracted
from all directions.

It's June, the time when
young male harbor seals

start their strange
mating displays.

One listens attentively
to the grunting noises

made by the other.

These calls
are almost certainly

a way of establishing which
of the two will be dominant.

But if the animals
are closely matched

in size and experience,
grunts won't settle the issue.

The rivals will have to
come to blows.

And seals can be
surprisingly violent.

In a month's time,
the breeding season will start,

and then,
fights will be in earnest.

But now, in midsummer,
these exchanges are harmless.

They're just playing.

Many of the creatures
that shelter in the kelp

have to venture out
in order to feed--

the bat ray,
for one.

Unlikely though it seems,

the sandy floor
of the open sea is,

for the bat ray,
a rich feeding ground.

There is food hidden
within the sand,

and the bat ray has a special
technique for finding it.

It uses jets of water
to blow the sand aside,

and expose
small invertebrates.

A kelp bass
hangs about alongside,

waiting for scraps.

Other hunters
are also on the prowl.

The fantailed sole.

There are mantid
shrimps here,

living in tunnels.

But, once again,

hunger compels them
to venture into the open.

That, of course,
is a gamble.

They will either eat...

...or be eaten.

A sea slug,
called Janolus.

Its colors suggest
that it's poisonous,

and so it is,

to everything except
another kind of sea slug.

The predatory Navanax.

Navanax pulls itself
along the trail of slime

that Janolus
leaves behind it.

Once caught,
Janolus rolls into a ball.

All Navanax gets is
a few yellow tentacles.

And Janolus is swept to safety
by the current.

It's now midsummer,

and the sun is shining
at full strength.

The increasing warmth
is the cue

for an Atlantic lobster
to start on a long journey.

She's spent the winter
250 meters down,

far beyond the reach
of the storms.

But it was cold
down there,

and now, she needs to find
warmer water,

so she's marching
towards the shallows.

They, however,
are 150 kilometers away.

After a month of walking,

she finally arrives
at her favored sandbank.

But she's not
the first here.

Dozens of
other lobsters

have already dug themselves
homes in the sand,

and they don't intend to
surrender them to newcomers.

Size counts for everything
in these battles.

The new arrival is
in urgent need of a pit,

and since she weighs
a hefty 7 kilos,

she stands a good chance
of getting one.

She's won.

These battles continue
for the next two months,

and they're crucial,

for the females must have
both shelter

and warm water if they're
to raise their young.

For the last seven months,
each of these females

has been carrying around
about 20,000 fertilized eggs.

But their task
is approaching its end.

The warmth of the shallows is
speeding the eggs' development.

Two more months
and the eggs are ready to hatch.

At first, they're not
very good at swimming,

but within
a few minutes,

the babies are able to set off
in a purposeful way.

At this time of the year,

the sea is full
of larval animals.

This one is
a one-day-old lobster.

And this,
a three-week-old crab,

just ready to start
its life on the seafloor.

Its feet touch the bottom
for the first time.

At this stage
in its life,

it's a vegetarian
with a taste for sea lettuce.

As it grows,
so it will repeatedly molt,

and expand into a bigger,
thicker skin.

The chances are
it will be eaten.

But if it survives
for five years,

it will have become
a magnificent armored giant.

Now, it eats meat,

and special adaptations
enable it to hunt in the dark.

Its jointed feet
are covered in sensors

which detect the slightest
chemical change

in its surroundings.

And as it walks
through the darkness,

its feet can literally
taste the sand.

As soon as it finds
suitable food,

it passes it forward
to its powerful crushing claws,

which make light work
of the soft flesh.

And those claws are also
very useful for defense.

A 1 1/2-meter-long
common octopus glides by.

The jet-propelled giant is
both powerful and very clever.

With octopus about,

it's risky for even a crab
to be in the open.

Even in the dark,

the octopus's eyes are sensitive
to the slightest movement.

Against a hunter like this,
the crab's claws are useless.

Late summer
in Southeast Alaska.

The water
is still warming,

and mysid shrimp are
swarming near the surface.

It's a final feast
for Pacific salmon

returning to the coast
from the open Pacific.

They're heading inshore
to breed,

and they arrive
in huge numbers.

They have to swim
far up the rivers to spawn,

but this river's level
is still too low.

They'll have to wait
until rain causes it to rise.

So, for now,
they are trapped in the sea

close to the shore--
the worst place to be.

A 3-meter-long
salmon shark,

a close relation
of the Great White.

This one has sensed
minute electrical signals

from the salmon nearby.

Shark can maintain
their blood temperature

at a higher level
than the surrounding sea water,

and that means they have
the energy to be quick.

Quicker, even,
than salmon.

Early autumn in Vancouver Island
in Canada,

600 miles to the south.

The ocean temperature
is slowly dropping.

40 meters below the surface,
this year's baby herring

are feeding on the last
of the summer's plankton.

Their movements attract
attention from the skies above.

Gulls can't dive, so, for now,
the fish are still safe.

But there are birds
which can dive.

Auklets and murres
swim effortlessly down

beneath the school.

The panicked herring are
forced towards the surface.

They gather into a giant
defensive ball of swirling fish.

The commotion attracts
yellowtailed rockfish.

They, too, are hunters.

The marauding fish
scatter the herring.

Repeated attacks split the ball
into numerous smaller groups.

Now, it's easier for the divers
to keep the confused fish

penned at the surface.

And there,
even the gulls can get at them.

Attacked from all sides,

the little fish
have virtually no chance.

More and more divers
are attracted to the scene.

They harry the shrinking
numbers of herring

right down to
the very last individual.

Far bigger predators
cruise here, too.

Pacific white-sided dolphin.

But the dolphin are mainly
nocturnal hunters.

During the day,
they concentrate on socializing.

They display by releasing
streams of bubbles,

and they play games.

Games like Pass the Seaweed,
for example.

Exactly eight months ago,
in the winter,

off the west coast
of Scotland,

an egg was laid, and securely
fixed to a strand of kelp.

Inside, a tiny embryo
started to develop.

Protected by
the tough egg case,

it endured the worst
of the winter storms.

By summer,
it was half grown.

Now, at last,
in the late autumn,

it's nearly ready
to hatch.

A fully formed
miniature shark swims free.

This year's plankton
will soon die,

but the young dogfish
is so well-developed

that it can hunt immediately
for larger prey.

The days are
getting shorter now.

In British Columbia,
the water begins to chill.

This bizarre-looking creature

is searching through
the kelp for food.

This is Melibe,
the hooded sea slug.

It catches plankton
with its net-like head.

As winter approaches,
plankton is becoming scarce,

but Melibe is
an assiduous searcher.

It can swim.

It flaps away to look for
a better feeding spot,

but its search is becoming
increasingly difficult.

Within the next
two weeks,

most of the plankton
will have disappeared.

As the sunlight
becomes ever more feeble,
the kelp starts to die,

gradually rotting away
to nothing.

Soon, it will be winter.

But 9,000 miles
to the south,

the sun is rising
on a new spring day.

The Southern Hemisphere, too,
has temperate regions,

and now, the plankton
is beginning to bloom

around Tasmania.

Just as in the north,
the southern seasonal seas

also have areas of rich,
green water,

with their own
kelp forests...

...and their own
swarms of plankton.

Some of the inhabitants
of these seas

live only in
the Southern Hemisphere.

This is one of them--
the handfish--

that strolls around
on modified fins.

But when needs must,
it can resort to tail power.

Every summer,

visitors come to the shallows
around Tasmania.

These are Australian squid,
about half a meter long.

They are here to breed.

The larger males compete for
the attentions of a female,

displaying towards her
and to one another

by putting on a ballet,
during which

they continually change
the color of their costumes.

Eventually,
they form pairs.

A male passes a packet of sperm
across to the female.

After the eggs
have been fertilized,

they are deposited in tough,
rubbery egg cases

that other creatures
find poisonous.

Within three weeks,

the babies are ready
to hatch out.

They are already able
to change color,

but they're not
quite so good at swimming.

There's another
animal here

that is a rather
more devoted parent.

This is a male
leafy seadragon,

an exquisitely decorated
relative of the seahorse.

He is carrying his
partner's eggs around with him.

They would be
a highly nutritious snack

for any predator
that found them,

but that's not easy,
because the eggs are attached

to their father's
perfectly camouflaged body.

They could scarcely be
in a safer place.

By November,
10,000 miles to the north,

winter has arrived.

Norway now gets less
than five hours of daylight

in every 24.

The temperature
is falling rapidly.

But despite the cold,
the sea is far from deserted.

Every winter, 500 million tons
of adult herring

seek shelter
in these deep waters.

They will stay here
for four months,

living entirely on the fat
they accumulated

during the summer feasts
of plankton.

But they are not alone.

Orca.

This small pod is part
of a population

of some 500 killer whales

that specialize in hunting
North Atlantic herring.

Using their echolocation,
they have detected

a shoal of herring
50 meters below them.

With enough air
for a 10-minute dive,

they swim deep below
the herring,

and drive the fish
upwards.

Bubbles stream
from the rising fish

as gas in their swim bladders
expands and escapes.

Even an orca finds it difficult
to catch a healthy herring,

but they have a devastating
weapon all their own.

They use their tail
to club the fish

with waves
of water pressure.

Then, it's simply a matter

of collecting
the stunned casualties.

The herrings
have no chance,

and both orca and gulls
will eat as much as they can

every day for
the next four months.

But there are so many fish
wintering here--

over five billion
individuals--

that the losses
are almost unnoticeable.

Violent as this
winter weather may be,

it's essential
for the renewal

of the riches
of the seasonal seas.

Out in the open oceans,

the surging waters stir up
nutrients from the depths.

By the end of winter,

the seasonal seas will be
full of minerals once more,

ready for the return
of the sun

and the next great
plankton bloom.