The Blue Planet (2001): Season 1, Episode 3 - Open Ocean - full transcript

These seas

- thousands of miles from nearest land

- are the most sterile on our planet.

These are marine deserts.

But here live the swiftest and the most
powerful of all ocean hunters

Simply finding them
is an immense challenge

but we are about to follow them
as they search for their food

in this little known part of the seas
- the open ocean.

Striped marlin - voracious predators...
that can grow to three metres long.

They hunt mainly in daylight

searching the tropical oceans from close



to the surface down to depths of
a hundred metres or so.

Normally the fish they feed on
are widely dispersed

but sometimes their prey gathers
in dense shoals, like these sardines.

This feast may last for over an hour,

time enough for other hunters
to reach the scene.

Juvenile tuna join in the feeding frenzy.

The noise attracts a giant - a sei whale.

It's fourteen metres long
and twenty tonnes in weight

- and has an appetite to match.

Soon the only sign that the sardines
ever existed are scales

sinking down into the abyss.

Such feasts don't last long.

Within a few short days,
waters that once swarmed...

with food will have been cleaned out.



The hunters must move elsewhere
and once again

start their search of the
seemingly featureless open ocean.

A manta ray - immense - five metres

across from the tip of one wing-like fin
to the tip of the other.

It's travelling economy,
wasting as little energy as possible,

as it glides through
the waters of the tropics.

The remora fish that accompany it travel

more economically still
- by hitching a lift.

Their host is searching for food
- plankton,

the minute fish and invertebrates
that float near the surface.

It needs lots of them
and may cruise for days before...

it finds a good feeding ground.

Dusk, at the edge of a Pacific Island

three thousand miles
from the nearest continent.

Here surgeon fish have assembled to spawn.

As they perform their nuptial dances

they discharge clouds of eggs
and sperm into the water.

The manta must have known this was about

to happen for it arrived at
exactly this critical moment.

And it is not the only one to do so.

Others are here too.

Now all they need to do is
to sweep the water into their mouths

and sieve out the eggs.

Within an hour,
the whole event will be over...

Any surviving eggs will be so dispersed

that they are not worth collecting.

But other perils await them as they join

the clouds of eggs
and larvae and tiny fish

that drift through the
surface waters of the open ocean.

These are the eggs of yellow fin tuna.

If the hatchlings survive, it will
take them two years to become adults.

In three years,
they could be nearly two metres long

and weigh two hundred kilograms.

Perhaps only one in a million
will live as long as that.

They and the other animals
and microscopic plants of the plankton

constitute the basis of all life
out on the open ocean.

A storm petrel dancing on the water.

But this is no amiable waltz.

It's a hunt.

As they hover facing into the wind,

they pick out morsels
from near the surface, including eggs.

Only a tiny percentage
of the developing eggs

will survive long enough to hatch.

These newly emerged tuna
are only three millimetres long

and although they can swim
they're still very vulnerable.

It will be many weeks before they can swim

strongly enough to make any
real headway in the ocean.

After the sun goes down,

other predators rise from the depths
to attack the floating multitudes.

Darkness shrouds the arrival of
battalions of dangerous drifting predators

These shimmering comb
jellies - sea gooseberries

- trap their prey
with sticky net-like webs

One ill-timed fin-stroke could bring
certain death to a hatchling fish.

There are many kinds of these comb jellies

- all of them very effective hunters.

By dawn, most of the nocturnal feeders

will have returned to the depths.

The surviving hatchlings,

however,
have already started on their travels.

Vast current systems,

like immense rivers,
carry them around the ocean basins.

The boundaries between
these masses of moving water...

form invisible barriers that can trap

both plankton and nutrients carried up
from the depths.

So parts of the ocean become rich

with food for days or even weeks at a time

This attracts vast schools of
plankton-feeding fish - like these sardine

They take in water through their mouths

and expel it through their gills

sieving out the plankton which
is then funnelled down their throats.

The immense schools travel along
the boundaries of the currents

- seeking the spots where
the plankton is thickest.

As the position of the current
boundaries changes constantly,

so does both the supply of plankton
and the numbers of fish.

A small pod of Pacific Spotted Dolphin

- twenty miles from the coast of Panama.

Like all predators,
they seek parts of the ocean

where their food is thickest.

They cover
as much as hundred miles in a day.

And while they travel, they play.

They have detected the sound of
schooling fish from hundreds of metres away

and start to track down
the shoals using sonar

- leaving their toys behind them.

For the hunted
there are few places to hide.

Schooling mackerel.

They have already sensed the sonar beams
of approaching dolphin.

Their only defence
is to gather into a ball.

Any individual that stayed out
of the shoal would be quickly picked off.

Within it,
there is at least some chance of survival.

The noise of the attack
alerts another predator

- a sailfish, one of the
fastest fish in the ocean.

It has detected rapid vibrations
in the water

and is searching for the cause.

Sailfish rely on eyesight

for their final approach

so they hunt mainly in daylight.

When sailfish become excited
they change colour

lighting up with bright blue stripes.

Since mackerel eyes
are especially sensitive

to blue and ultraviolet,
these colours confuse them

- making them easier to catch.

Far below, a blue shark returns
from a squid-hunting trip in the

cold darkness three hundred metres down.

It's heading for the surface to
reheat in the warmer water.

As it ascends,
it detects the smell of oils

and proteins shed into the water
by the panicked mackerel.

The trail leads both the shark

and its attendant pilot fish
towards an easy meal.

Scraps and casualties float

in the wake of the passing mackerel school

Throughout the ocean,
predators and prey are locked

in a deadly three-dimensional
contest of hide and seek

played out over immense distances.

To survive they must travel.

The huge four metre long blue-fin tuna

has special blood vessels that enable it

to keep its body temperature significantly
warmer than the surrounding water.

As a result,
they can survive in much colder conditions

than any other tuna
and they travel thousands of

miles away from their spawning grounds

in the tropics to hunt in cold seas

where the food supply is richest.

Ocean travellers come in many guises

- and few are stranger than this...

crab that spends much of its life afloat.

It is a worrying passer-by
for booby birds with delicate toes.

Many floaters are little more than jelly,

enclosed in membranes,
but they may drift for vast distances.

And turtles, like these olive ridleys,
migrate thousands of miles every year.

The ocean is full of such wanderers,

riding the currents, and doing their best

to avoid enemies while
they search for food

and a safe place to breed...

Which is exactly what these rays are doing

- forming the two-mile-high-club,

gathering together
for courtship on the wing,

far above the ocean floor.

More nomads - flying fish.

They seem to be
on every large predator's menu,

so their whole life is spent
on the run in the open ocean.

They don't scatter their eggs

but lay them on pieces of flotsam
like this palm frond.

If the quality of water is right,

they will attach their eggs to the frond,

which will then serve as a kind
of life-raft for their offspring.

But it's not only flying fish
that seek nurseries.

Any piece of floating debris can serve
as a shelter under which baby fish can hide

The only draw back, is that predators

like this wahoo always check up on

who's hanging about in the shadows.

The wahoo may trail the flotsam for weeks.

Few bits of flotsam are without their

quota of lodgers - even man-made
junk attracts them.

And some, like this oceanic trigger fish,

defend their squatters rights with vigour

The triggers, in fact,
tend to claim all the prime residences.

Out here,
even discarded netting can provide

valuable shelter, so

- in a bizarre twist

- a wrecked trawl net like this can end up
as a sanctuary for fish

- until such time as it finally sinks.

Indeed, a single large piece of flotsam

can be the reason why several
square miles of open ocean,

instead of being empty, will support
a fish population of hundreds of tonnes.

This huge clump of seaweed
is doing exactly that.

It is a giant kelp plant, ripped from
the rocks off the coast of California.

Now, it's floating above thousands
of metres of water,

held up by its gas filled floats.

Clouds of young rockfish are growing up
in the safety of its shadow.

Giants also seek out this algal flotsam.

This is a sunfish.

It can measure as much as four metres
from fin-tip to fin-tip.

Rather surprisingly, it has the record
as the heaviest bony fish in the sea.

Sunfish spend much of their time at
depth where they feed on jellyfish;

but it is cold and dark down there
so from time to time,

they seek a little rest and recuperation
and warm up near the surface.

They too are looking for floating
kelp plants.

Not for shelter but because here they

can find a particular kind of fish
that only lives in such places.

Half moon fish.

The sunfish form up in an orderly queue.

They have a problem.

Their skin is covered in parasites.

The hungry half-moons will help.

The sunfish turn their heads towards

the surface as a clear invitation
to their personal hygienists.

The half-moons nip off - and eat

- every parasite they can find.

If the half moons don't do the job

- there is another rather drastic
treatment available here.

Gulls rest on the floating kelp.

And if the sunfish
send the right signals...

the gulls will investigate.

Their beaks can dig out
the most stubborn parasites.

But even the very best of health clinics
can only trade on a temporary basis.

The seaweed rafts are rotting

and will eventually lose their buoyancy.

Then their lodgers
will have to find a new home.

If they can't, they will be eaten,

or die and sink down into the abyss.

But the open ocean is not entirely
devoid of permanent shelter.

A volcano is erupting from the seafloor
and it is still growing.

It has formed an island some seventy miles
from the coast of New Zealand.

Some juvenile reef fish
have already arrived,

carried here by a lucky current.

Now they are growing up in the shelter of

the weeds growing around
the island's fringes.

More plankton and juvenile fish

are being swept by currents straight
towards the island.

But now there is a welcoming committee.

Schools of trevally and blue maomao

are patrolling the surface water.

All are in search of a meal.

These one kilo fish snap up
every morsel of plankton they find.

At times, the currents sweeping in from

the open ocean bring with them all kinds
of small creatures in dense concentrations

These are mysid shrimps.

Very little that is edible
is left after such feasts.

Islands are far from being safe
havens for plankton.

The Pacific Ocean, however,

is peppered with
over twenty three thousand...

slands as well as
countless other submerged mountains

- sea mounts - whose summits
do not break the surface.

Juvenile fish, for their first few months

would do well to avoid such places.

These yellow-fin tuna, however,

are now more than six months old
and forty centimetres long

- big enough to be able to eat fry,

- so sea mounts for them are promising

feeding grounds where they may
hunt for several months.

The base of a seamount.

As currents sweep towards it they are
deflected up its towering walls.

The water, coming from the depths,

carries both nutrients and
plankton to the surface.

Numerous reef fish take up
permanent residence here,

feeding where the currents are strongest

and the plankton most dense.

Where the cold water mixes with
warmer water at the surface,

there is a strange shimmering effect

- a clear sign that the currents
are running strongly.

But these currents attract
more than just coastal fish.

Giants come here from the open ocean....

Hammerhead sharks - and in great numbers.

During the day, they circle the sea mount
looking for small fish at the reef edges.

But not in order to eat them.

They, like the sunfish,

are looking for cleaners to rid
them of their parasites.

White-tip reef sharks gather here too.

They do eat reef fish.

But they prefer to hunt at night,

when the reef fish are sleepy
and easier to catch.

Far better to rest by day and
allow the cleaners to do their work...

Even swarms of breeding trigger
aren't a serious temptation.

These triggers spend much of
their time in open water,

but they have come
to the seamount to spawn.

Trigger eggs are good food

and the plankton-feeders gather what they
can before the current sweeps them away.

This whole community is only here

because of the nutrients and plankton

that the seamount deflected into
the surface waters.

But ocean-going hunters
are never far away.

Silky shark specialise in picking off

injured fish and constantly check over

the residents around the seamount.

At some times of the year,

seasonal changes make the currents
especially rich in nutrients

and then the ocean around the seamount

becomes a virtual soup of plankton.

At such times, hunters gather
in astonishing numbers.

Bonito, smaller relatives of the tuna.

They are searching
for still smaller plankton

feeders that have been
attracted by the bloom.

So are these jacks
- and their prey is nearby.

A school of anchovetta has strayed up
near the surface,

even though it is broad daylight

and hunters are on the prowl.

These small fish can already feel

the vibrations
of the approaching predators.

Swimming at speed,
they have formed into a ball

and now they must wait for whatever comes.

They're been detected.

At first the sheer scale of the bait ball
seems to daunt the predators.

But now the bonito arrive
and launch the first attack.

Still the bait ball holds together.

The young yellow fin tuna move in.

The speed of this attack is so great

that gradually groups of anchovetta are
splintered from the main fish ball.

Before long the currents will shift

and the ocean will become once more
a blue tropical desert, plankton free.

And the hunters will have to move on.

Spinner dolphins,
still searching for food.

Their twisting leaps are, apparently,
purely social displays.

Since the hunting has been good

many hundred have gathered together
in this exuberant super-pod.

But now the spinners are
starting to hunt once more.

Their skill in tracking food
is not a secret.

Yellow-fin tuna must be aware of it
for they regularly follow them.

But only adult tuna in their second

or third year of life
have sufficient stamina

to keep up with the fast-moving spinners.

These are another kind - Common Dolphin.

They too are on the move.

As they travel - ever inquisitive

they pay a call on one of their
larger relations

- a pilot whale.

The whale is not hunting.

It's on its way to its breeding grounds
in the Mediterranean.

Pilot whales normally hunt in
small family groups but in mid-summer

they head for
traditional socialising grounds

where they will assemble in
super herds several hundred strong.

Already two families have joined together.

The males are starting to compete
for the favours of the females.

As the weeks pass by these group rubbing-
sessions will become more overtly sexual.

But now - it's just flirting in the sun.

Timing in the ocean can be crucial.

In summer, the northern Atlantic waters
are beginning to warm.

The hunting is good here
and by June predators

from southern waters are
heading towards the Azores.

These are more Common Dolphin.

Like most oceanic dolphins

they too often travel in huge herds
containing many different families.

There is seldom enough prey in
any one place to feed such numbers.

So small groups leave the super-pod
and set off on hunting expeditions.

This group will be away from
the main herd for several hours.

By mid-day they're nearing
the Islands of the Azores

- nine hundred miles west
of the Portuguese coast.

Other hunters are already here
- Cory's Shearwaters.

Half a million of these birds breed on
the Azores every year

and scour the nearby ocean for food.

Right now there is insufficient wind

to support gliding flight
and since flapping

is a waste of energy they sit out the calm

clustered in rafts
and riding the gentle swells.

By mid-afternoon the dolphin are
starting to hunt in earnest.

As the sea breeze picks up,

the shearwaters take to the air once more.

Out to sea, the dolphin have found prey....

They are driving a shoal of
small mackerel up towards the surface.

The shearwaters crowd the skies above,

following the dolphins' every turn.

The mackerel are still some metres down.

But when the baitfish
come sufficiently close,

the airborne division makes its move.

Far from being mere bystanders,

the shearwaters can now become
underwater predators themselves.

Incredibly they can dive down to
depths of several metres.

The hunting dolphin prevent the mackerel

from escaping downwards and
both predators gorge themselves.

Soon the diving birds outnumber the dolphin
and even drive them away from their meal.

But another squadron of predators
arrives to replace the dolphin.

Adult yellow-fin tuna.

These are giants - two metres long.

They are heading directly
for the bait ball.

Despite the arrival of the giant fish,

the shearwater continue to
press home their attack unfazed.

Eventually the tuna move on, leaving the
shearwaters to battle among themselves.

As long as a predatory fish or a dolphin

remains at the scene the
mackerel can't escape to safety.

But when the little skipjack tuna
start to move away,

gradually the bait ball begins to sink
in to the depths towards safety.

The shearwaters follow it down to the
very limit of their breath-holding ability

perhaps as deep as fifteen metres.

At last, even they are forced
to leave their quarry.

However good or bad
this summer's feeding may be

within three months winter will be

on its way and the temperature of these
waters will drop by a few degrees.

Then the ocean hunters will
abandon the Azores once more.

As ever, they will move on - searching for
another feeding opportunity,

the next pulse of life in the distant
reaches of the Open Ocean.