The Blue Planet (2001): Season 1, Episode 1 - Ocean World - full transcript
The ocean's influence dominates the world's weather systems and supports an enormous range of life. This first episode demonstrates the sheer scale, power and complexity of the "Blue Planet".
Dwarfed by the vast expanse
of the open ocean
the biggest animal
that has ever lived on our planet.
A blue whale, 30 metres long
and weighing over 200 tonnes
It's far bigger
than even the biggest dinosaur
Its tongue weighs as much as an elephant
Its heart is the size of a car
And some of its blood vessels are so wide
that you could swim down them
Its tail alone is the width
of a small aircraft wings
Its streamlining, close to perfection,
enables it to cruise at twenty knots
It's one of the fastest animals in the sea
The ocean's largest inhabitant feeds
Almost exclusively on one of the smallest
krill, a crustacean
just a few centimetres long
Gathered in a shoal,
krill stain the sea red and a single blue
whale in a day
can consume forty million of them
Despite the enormous size of blue whales,
we know very little about them
Their migration
routes are still a mystery and
we have absolutely no idea
where they go to breed
They are a dramatic reminder of how much
we still have to learn about the ocean and
the creatures that live there
Our planet is a blue planet
Over seventy percent of
it is covered by the sea
The Pacific Ocean
alone covers half the globe
You can fly across it non-stop
for twelve hours
and still see nothing
more than a speck of land
This series will reveal the complete
natural history of our ocean planet from
its familiar shores to the mysteries
of its deepest seas
By volume, the ocean makes up 97% of
the earth inhabitable space
And the sheer quantity of marine life
it contains far exceeds that
which inhabits the land
But life in the ocean
is not evenly spread.
It's regulated by the path
of currents carrying nutrients
and the varying power of the sun
In this first programme
we will see how these two forces interact
to control the distribution of life
from the coral seas ...to the polar wastes
The sheer physical power
of the ocean dominates our planet
It profoundly influences
the weather of all the world
Water vapour rising
from it forms the clouds
and generates the storms that ultimately
will drench the land
The great waves
that roar in towards the shores
are dramatic demonstrations of its power
Waves originate far out at sea
There,
even gentle breezes can cause ripples
and ripples grow into swells
Out in the open ocean, unimpeded by land,
such swells can become gigantic
It's only when an ocean swell
eventually reaches shallow water
that it starts to break
As it approaches the coast
the water at the bottom of the swell
is slowed by contact with the sea bed
The top of the swell,
still travelling fast,
starts to roll over
and so the wave breaks
The ocean never rests.
Huge currents, such as the Gulf Stream,
keep its waters constantly
on the move all round the globe
It's these currents
more than any other factor
that control the distribution of
nutrients and life in the seas
A tiny island lost in the midst
of the Pacific
It's the tip of a huge mountain
that rises precipitously from
the sea floor thousands of metres below
The nearest land
is three hundred miles away
Isolated sea mounts
like this one create oases
where life can flourish...
in the comparatively empty expanses
of the open ocean
But all the creatures
that swim beside it would
not be here were it not for
one key factor - the deep ocean currents
Far below the surface they collide with
the island's flanks
and are deflected upwards
bringing with them from the depths
a rich soup of nutrients
Such up-wellings
attract great concentrations of life
Most of the fish here
are permanent residents,
feeding on the plankton, the tiny floating
plants and animals that are nourished
by the richness brought up from the depths
And they in turn,
attract visitors from the open ocean
Tuna.
The plankton feeders are easy targets
All this action attracts
even larger predators...
Sharks!
Hundreds of sharks.
These silky sharks are
normally ocean-going species
but the sea mounts in the eastern Pacific,
like Cocos, Malpelo and the Galapagos,
attract silkies in huge groups
up to five hundred strong
Silkies seem to specialize
in taking injured fish
and constantly circle sea mounts on
the look out for the chance to do so
But Silkies are not the only visitors
Hammerheads gather
in some of the largest shark
shoals to be found anywhere in the ocean
Sometimes thousands will circle
over a single sea mount
But these sharks are not here for food
They have come for another reason
Some of the locals
provide a cleaning service
Following the last El Nino year,
when a rise in water temperatures
caused many sharks to suffer
from fungal infections,
the number of hammerheads visiting the sea
mounts reached record levels
Nutrients also well up to the surface
along the coasts of the continents
This is Natal
on South Africa's eastern seaboard
It's June and just off-shore,
strange black patches have appeared
They look like immense oil
slicks up to a mile long
But this is a living slick
Millions and millions
of sardines on a marine
migration that in terms of sheer biomass
rivals that of the wildebeest
on the grasslands of Africa
These fish live for most of the time
in the cold waters south of the Cape,
but each year the coastal currents reverse
The warm Agulhas current that
usually flows down from the north
has been displaced by cold water
coming up from the south
and that has brought up rich nutrients
They, in turn,
have created a bloom of plankton
- and the sardines are now feasting on it
As the sardines travel north,
a whole caravan of predators follow them
Thousands of Cape Gannets
track the sardines
They nested off the Cape
and timed their breeding so that
their newly-fledged chicks
can join them in pursuing the shoals
Below water, hundreds of sharks
have also joined the caravan
These are Bronze whaler sharks,
a cold water species that normally
lives much further south
These three-metre sharks
cut such great swathes
through the sardine shoals that their
tracks are clearly visible from the air
Harried by packs of predators and
swept in by the action of the waves,
the sardine shoals are penned
close to the shore
Common dolphin are coming in
from the open ocean to join the feast
There are over a thousand of them
in this one school
When they catch up with the sardines,
the action really begins
Working together,
they drive the shoal towards the surface
It is easier for the dolphins
to snatch fish up here
Now the sardines have no escape
Thanks to the dolphins, the sardines have
come within the diving range of the gannets
Hundreds of white arrows shoot
into the sea,
leaving long trails
of bubbles behind each dive
Next to join the frenzy are the sharks
Sharks get very excited
when dolphins are around
That may be because
they can feed particularly...
well once the dolphins have driven
the sardines into more compact
groups near the surface
As the frenzy continues walls of
bubbles drift upwards
They are being released by the dolphins,
working together in teams
They use the bubbles to corral the
sardines into ever tighter groups
The sardines seldom cross the wall of
bubbles and crowd closer together
Bubble netting in this way enables the
dolphins to grab every last trapped sardine
Just when the feasting
seems to be almost over,
a Bryde whale arrives
The survivors head on northwards,
and the caravan of predators follows them
Nutrients can also be brought up
- though less predictably
- - by rough weather
Particularly near the poles,
huge storms stir the depths and
enrich the surface waters and here,
in the South Atlantic,
the seas are the roughest on the planet
And very rich seas they are too, for here,
the cold Falklands current from the South
meets the warm Brazil
current from the North
and at their junction
there is food in abundance
These Black-browed
albatross are duck-diving
for krill that has been driven up
to the surface
Like all albatross,
Black-brows are wanderers
across the face of the open ocean
A feeding assembly on this scale
is a rare sight
Most of the time,
the birds of the open sea
are widely dispersed
But these feeding grounds are close
to an albatross breeding colony
- and a very special one
This is Steeple Jason, a remote island
in the far west of the Falklands
It has the largest albatross
colony in the world
There are almost half a million
albatross here
an astonishing demonstration of
how fertile the ocean can be
and how much food it can give even to
creatures that do not actually live in it
Nutrients by themselves are not enough to
generate these vast assemblies.
The heat and light
that the sun brings everyday
is also essential for the growth of
the microscopic floating plants
- the phytoplankton
And it the phytoplankton
that is the basis of all life in the ocean
Every evening,
the disappearance of the sun
below the horizon triggers the largest
migration of life
that takes place on our planet
One thousand million tones
of sea creatures
ascend from the deep ocean to
search for food near the surface
They graze on the phytoplankton
under cover of darkness
Even so, they are far from safe
Other marine hunters follow them,
some travelling up
from hundreds of metres below
At dawn, the whole procession returns
to the safety of the dark depths
The moon too has a great
influence on life in the oceans
Its gravitational pull creates the daily
advance and retreat of the tides
But the moon has
more than a daily cycle
Each month it waxes and wanes
as it travels around the earth,
and this monthly cycle also
triggers events in the ocean
The Pacific Coast of Costa Rica
on a very special night
It just after midnight
and the tide is coming in
The moon is in its last quarter,
exactly half way between full and new
For weeks the beach has been empty
But that is about to change
At high tide,
turtles start to emerge from the surf
At first they come in ones and twos,
but within a hour,
they are appearing all along the beach
They are all female Ridley turtles
and over the next six days or so
four hundred thousand
will visit this one beach
to lay their eggs in the sand
At the peak time, five thousand
are coming and going every hour
The top of the beach gets so crowded that
they have to clamber over one
another to find a bare patch
where they can dig a nest hole
A quarter of the world population
of Ridley turtles come to this one beach
on a few key nights each year
The rest of the time, they are widely
distributed through the ocean
searching for food, most
-a hundreds of miles away from here
This mass nesting is called an arribada
How it is co-ordinated is a mystery
- but we do know that's arribadas start
when the moon is either in its first
or its last quarter
Forty million eggs
are laid in just a few days
By synchronising their nesting in this way
the females ensure that six weeks later
their hatchlings
will emerge in such enormous...
numbers that predators on the beach
are overwhelmed
and a significant proportion
of the baby turtles will get past them
and make it to the water
But why do the females
use a cue from the moon
to help in synchronising their nesting?
Part of the answer to that becomes clear
at dawn on the following morning
The day shift of predators are arriving
for their first meals
Vultures have learnt
that the returning tide
can wash freshly laid eggs out of the sand
The risk of eggs being exposed by the surf
may be part of the reason
why turtle arribadas
tend to occur around the last
or first quarter of the moon
It's on such days as this,
when the moon is neither full nor new,
that the tides are weakest and
the sea is likely to be calmer
So at these times,
it easier for the female turtles
to make their way through the surf
and there less chance of their eggs
being washed out of the sand
and being taken by the vultures
The moon monthly cycle
and its influence on the tides triggers
many events in the ocean,
from the spawning of the corals
on the Great Barrier reef
to the breeding cycles of fish
But there an even longer rhythm
that has the most profound effect of all
- the annual cycle of the sun
The sun position relative
to the earth changes
through the year and
it this that produces the seasons
In the north, spring comes as the sun
begins to rise higher in the sky
Off the coast of North West America,
the seas are transformed by the increasing
strength of the sunshine
Here in Alaska the coastal waters turn
green with a sudden bloom of phytoplankton
Herring that have spent
the winter far out to sea,
time their return to the shallow waters
to coincide with this bloom
They come in vast numbers and initiate
one of the most productive
food chains in all the oceans
Humpback whales are at the top
of that food chain
They have spent the winter breeding
in the warmer tropical waters off Hawaii
But there was little food for them there
This herring bonanza provides the vast
majority of their food for the year
Stellar and Californian sea lions
also return from the open ocean
each year to feast off the herring
The herring themselves,
however, have not come here for food
They are about to breed
Nothing deters them as they head
for even shallower waters
Now the waters
are so shallow that glaucous
-winged gulls are able to snatch live fish
from just below the surface
In spite of these attacks and losses,
the herring swim on until
they reach the vegetation that the females
need if they are to lay
Each female produces
around twenty thousand eggs
- and they every sticky
The males arrive soon after the females
have spawned and release their sperm
in vast milky clouds
Soon the excesses
of the herrings' sexual spree
creates a thick, white scum on the surface
Through the season curds of sperm clog
the shores for hundreds of miles,
from British Columbia in the South
all the way to Alaska in the north
After a few days this gigantic spawning
comes to an end and the herring head
back out to deeper waters,
leaving behind them
fertilised eggs plastered...
on every rock and strand of vegetation
They time their spawning
so that two weeks later,
when these eggs start to hatch,
the annual plankton bloom
will have reached
its height and the new-born fish fry
will have plenty to eat
But in the meantime,
all these eggs provide food
for armies of different animals both below
and above the surface
Millions of birds arrive to collect
a share of the herring bounty
Some of it is easily gathered,
for millions of eggs have been
washed up onto the shore
This encapsulated energy is particularly
valuable to migrating birds
These surfbirds are on their way
to their breeding grounds in the Arctic
and they have to come down to refuel
Stranded herring eggs
are just what they need
Bonaparte gulls collect the eggs
just below the surface of the water
Further out in the bay,
huge flocks of ducks have gathered
They are mostly surf scoters
- diving ducks - that can feed off
the bottom several metres down
There are such huge quantities of eggs
that even such a big animal as a bear
finds it worthwhile to collect them
The spawning of the herring
is a crucial event
in the lives of many animals
all along the coast
The whole event coincides
with the plankton bloom
and within just three short weeks
it all over
The migratory birds leave
to continue their journey north
They will not come back until
the herring also return next year
As the herring spawning finishes,
other migrants are starting
to arrive just offshore
Grey whales
They have followed the sun north
and they too are seeking the food
that is generated by
the bloom of the phytoplankton
Krill are feeding off it and these
whales are feeding on the krill,
skimming it from the surface
with the filter plates of baleen
that hang from their upper jaws
Grey whales make one
of the longest migrations
undertaken by any marine mammal
- a round trip of 12,000 miles or
so from their breeding grounds off Mexico
along the entire coast of North America
right up to the Arctic ocean
They travel close to the coast
with the males
and non-breeding females leading the way
The last to start are the cows
that have just given birth
They have to wait until
their new-born calves
are sufficiently big and strong to tackle
such an immense journey
Their progress is necessarily slow
The mothers must stay
alongside their young
and even a strong calf can only travel
at a couple of knots
They stick even closer to the shore
often within just 200 metres
Killer whales.
They have learnt that grey whales
follow traditional routes
The killers have no trouble in overtaking
a calf and its devoted mother
Normally,
they continually call to one another,
but now they have fallen silent
The mother grey whale and her calf
have no idea that they have been targeted
Catching up with the grey whales
is the easy part for the killers
They have to be cautious
for they are only...
about half the size
of the grey whale mother
She can inflict real damage with her tail
But the killers are not after her
They are after her calf
As long as the mother
can keep it on the move,
it will be safe and
she does her best to hurry it along
At first the killers
avoid getting too close...
to the mother but just keep pace alongside
They know that the calf,
going at this speed, will eventually tire
After three hours
of being harried in this way
the calf becomes too exhausted
to swim any further
The mother has to stop
This is the moment the killers
have been waiting for
They start to try and force themselves
between mother and calf
A calf, separated from its mother,
will not be able to defend itself
Time and again the black fins
of the killers appear between
the mottled backs of the grey whales
At last the killers succeed
And now that they've got the calf
on its own, they change their tactics
They leap right on to the calf
and try to push it under
They are trying to drown it
The calf snatches a desperate breath
The mother becomes increasingly agitated
Frantically,
she tries to push her calf back
to the surface so that it can breathe
But now it is so exhausted that it has
to be supported by its mother's body
The killers won't give up
Like a pack of wolves,
they take turns in harassing the whales
Now the whole pod is involved
One of them takes a bite
Soon the sea is reddened
with the calf's blood
and the killers close in for the final act
The calf is dead
After a six-hour hunt, the killer whales
have finally won their prize
The mother, bereft, has to continue
her migration north on her own
She leaves behind the carcass
of a calf that
she cherished
for thirteen months in her womb
for which she delayed
her own journey to find food
The pod of fifteen killer whales spent
over six hours trying to kill this calf
But now, having succeeded,
they have eaten nothing
more than its lower jaw and its tongue
Valuable food like this will not
go to waste in the ocean
Before long the carcass will sink
to the very bottom of this deep sea
But even there,
its flesh will not be wasted
Over a mile down in the
total darkness of the deep ocean
- the body of another grey whale,
a thirty ton adult
It settled here only a few weeks ago
Already,
it has attracted hundreds of hagfish
These scavengers, over half a metre long
and as thick as your arm,
are only found in the deep sea
They have been attracted
by the faint whiff of
decay suffusing through the water
for miles around
With their heads buried
in the whale's flesh,
they breathe through gill openings
along the sides of their bodies
They're very primitive creatures
- not even true fish, for they lack jaws.
- They feed, not by biting, but by
rasping off flesh
with two rows of horny teeth
In just a few hours,
a hagfish can eat several times
its own weight of rotting flesh
Next to arrive - a sleeper shark
It moves so slowly to conserve energy
- an important strategy for so large
an animal surviving in such a poor habitat
Sleeper sharks live over a mile down
and grow to over seven metres long
They can go for months without food,
slowly cruising along the bottom,
waiting for rare bonanzas,
such as this one, to arrive from above
A whole range of different
deep-sea scavengers
will feast on this carcass for a long time
before all its nutriment has been consumed
Eighteen months later, all that is left
is a perfect skeleton, stripped bare
The sun's energy that was captured
and turned into living tissue
by the floating
phytoplankton has been transferred from
one link to another in the food chain
and has ended up as far away from the sun
as it is possible to be on this planet
- at the bottom of the deep sea
But some energy also returns from the deep
Millions of opalescent squid are
on their way to the shallows
They have come up here to mate
As the males grab the females,
their tentacles flush red
For most of the year these squid
live at a depth of around 500 metres
They only come together in these great
breeding schools for a few weeks
Just one school was estimated to contain
animals that weigh around 4000 tonnes
Wave after wave rise from the depths
and soon the seabed
in the shallows is strewn
with dense patches of egg capsules
several metres across
As each female adds
another capsule to the pile
the males fight to fertilise its contents
The squid make their huge journey
into the shallows because their eggs
will develop faster
in the warmer water here
and when the young emerge,
they will find more
food more easily than
they would in the ocean depths
Dawn the next morning and the seabed for
miles around is covered in egg capsules.
The squid themselves have all gone
Many will have died, but some will have
returned to their home in the deep
They will not return
to the light of the sun
until the next time they are driven up
by the urge to spawn
of the open ocean
the biggest animal
that has ever lived on our planet.
A blue whale, 30 metres long
and weighing over 200 tonnes
It's far bigger
than even the biggest dinosaur
Its tongue weighs as much as an elephant
Its heart is the size of a car
And some of its blood vessels are so wide
that you could swim down them
Its tail alone is the width
of a small aircraft wings
Its streamlining, close to perfection,
enables it to cruise at twenty knots
It's one of the fastest animals in the sea
The ocean's largest inhabitant feeds
Almost exclusively on one of the smallest
krill, a crustacean
just a few centimetres long
Gathered in a shoal,
krill stain the sea red and a single blue
whale in a day
can consume forty million of them
Despite the enormous size of blue whales,
we know very little about them
Their migration
routes are still a mystery and
we have absolutely no idea
where they go to breed
They are a dramatic reminder of how much
we still have to learn about the ocean and
the creatures that live there
Our planet is a blue planet
Over seventy percent of
it is covered by the sea
The Pacific Ocean
alone covers half the globe
You can fly across it non-stop
for twelve hours
and still see nothing
more than a speck of land
This series will reveal the complete
natural history of our ocean planet from
its familiar shores to the mysteries
of its deepest seas
By volume, the ocean makes up 97% of
the earth inhabitable space
And the sheer quantity of marine life
it contains far exceeds that
which inhabits the land
But life in the ocean
is not evenly spread.
It's regulated by the path
of currents carrying nutrients
and the varying power of the sun
In this first programme
we will see how these two forces interact
to control the distribution of life
from the coral seas ...to the polar wastes
The sheer physical power
of the ocean dominates our planet
It profoundly influences
the weather of all the world
Water vapour rising
from it forms the clouds
and generates the storms that ultimately
will drench the land
The great waves
that roar in towards the shores
are dramatic demonstrations of its power
Waves originate far out at sea
There,
even gentle breezes can cause ripples
and ripples grow into swells
Out in the open ocean, unimpeded by land,
such swells can become gigantic
It's only when an ocean swell
eventually reaches shallow water
that it starts to break
As it approaches the coast
the water at the bottom of the swell
is slowed by contact with the sea bed
The top of the swell,
still travelling fast,
starts to roll over
and so the wave breaks
The ocean never rests.
Huge currents, such as the Gulf Stream,
keep its waters constantly
on the move all round the globe
It's these currents
more than any other factor
that control the distribution of
nutrients and life in the seas
A tiny island lost in the midst
of the Pacific
It's the tip of a huge mountain
that rises precipitously from
the sea floor thousands of metres below
The nearest land
is three hundred miles away
Isolated sea mounts
like this one create oases
where life can flourish...
in the comparatively empty expanses
of the open ocean
But all the creatures
that swim beside it would
not be here were it not for
one key factor - the deep ocean currents
Far below the surface they collide with
the island's flanks
and are deflected upwards
bringing with them from the depths
a rich soup of nutrients
Such up-wellings
attract great concentrations of life
Most of the fish here
are permanent residents,
feeding on the plankton, the tiny floating
plants and animals that are nourished
by the richness brought up from the depths
And they in turn,
attract visitors from the open ocean
Tuna.
The plankton feeders are easy targets
All this action attracts
even larger predators...
Sharks!
Hundreds of sharks.
These silky sharks are
normally ocean-going species
but the sea mounts in the eastern Pacific,
like Cocos, Malpelo and the Galapagos,
attract silkies in huge groups
up to five hundred strong
Silkies seem to specialize
in taking injured fish
and constantly circle sea mounts on
the look out for the chance to do so
But Silkies are not the only visitors
Hammerheads gather
in some of the largest shark
shoals to be found anywhere in the ocean
Sometimes thousands will circle
over a single sea mount
But these sharks are not here for food
They have come for another reason
Some of the locals
provide a cleaning service
Following the last El Nino year,
when a rise in water temperatures
caused many sharks to suffer
from fungal infections,
the number of hammerheads visiting the sea
mounts reached record levels
Nutrients also well up to the surface
along the coasts of the continents
This is Natal
on South Africa's eastern seaboard
It's June and just off-shore,
strange black patches have appeared
They look like immense oil
slicks up to a mile long
But this is a living slick
Millions and millions
of sardines on a marine
migration that in terms of sheer biomass
rivals that of the wildebeest
on the grasslands of Africa
These fish live for most of the time
in the cold waters south of the Cape,
but each year the coastal currents reverse
The warm Agulhas current that
usually flows down from the north
has been displaced by cold water
coming up from the south
and that has brought up rich nutrients
They, in turn,
have created a bloom of plankton
- and the sardines are now feasting on it
As the sardines travel north,
a whole caravan of predators follow them
Thousands of Cape Gannets
track the sardines
They nested off the Cape
and timed their breeding so that
their newly-fledged chicks
can join them in pursuing the shoals
Below water, hundreds of sharks
have also joined the caravan
These are Bronze whaler sharks,
a cold water species that normally
lives much further south
These three-metre sharks
cut such great swathes
through the sardine shoals that their
tracks are clearly visible from the air
Harried by packs of predators and
swept in by the action of the waves,
the sardine shoals are penned
close to the shore
Common dolphin are coming in
from the open ocean to join the feast
There are over a thousand of them
in this one school
When they catch up with the sardines,
the action really begins
Working together,
they drive the shoal towards the surface
It is easier for the dolphins
to snatch fish up here
Now the sardines have no escape
Thanks to the dolphins, the sardines have
come within the diving range of the gannets
Hundreds of white arrows shoot
into the sea,
leaving long trails
of bubbles behind each dive
Next to join the frenzy are the sharks
Sharks get very excited
when dolphins are around
That may be because
they can feed particularly...
well once the dolphins have driven
the sardines into more compact
groups near the surface
As the frenzy continues walls of
bubbles drift upwards
They are being released by the dolphins,
working together in teams
They use the bubbles to corral the
sardines into ever tighter groups
The sardines seldom cross the wall of
bubbles and crowd closer together
Bubble netting in this way enables the
dolphins to grab every last trapped sardine
Just when the feasting
seems to be almost over,
a Bryde whale arrives
The survivors head on northwards,
and the caravan of predators follows them
Nutrients can also be brought up
- though less predictably
- - by rough weather
Particularly near the poles,
huge storms stir the depths and
enrich the surface waters and here,
in the South Atlantic,
the seas are the roughest on the planet
And very rich seas they are too, for here,
the cold Falklands current from the South
meets the warm Brazil
current from the North
and at their junction
there is food in abundance
These Black-browed
albatross are duck-diving
for krill that has been driven up
to the surface
Like all albatross,
Black-brows are wanderers
across the face of the open ocean
A feeding assembly on this scale
is a rare sight
Most of the time,
the birds of the open sea
are widely dispersed
But these feeding grounds are close
to an albatross breeding colony
- and a very special one
This is Steeple Jason, a remote island
in the far west of the Falklands
It has the largest albatross
colony in the world
There are almost half a million
albatross here
an astonishing demonstration of
how fertile the ocean can be
and how much food it can give even to
creatures that do not actually live in it
Nutrients by themselves are not enough to
generate these vast assemblies.
The heat and light
that the sun brings everyday
is also essential for the growth of
the microscopic floating plants
- the phytoplankton
And it the phytoplankton
that is the basis of all life in the ocean
Every evening,
the disappearance of the sun
below the horizon triggers the largest
migration of life
that takes place on our planet
One thousand million tones
of sea creatures
ascend from the deep ocean to
search for food near the surface
They graze on the phytoplankton
under cover of darkness
Even so, they are far from safe
Other marine hunters follow them,
some travelling up
from hundreds of metres below
At dawn, the whole procession returns
to the safety of the dark depths
The moon too has a great
influence on life in the oceans
Its gravitational pull creates the daily
advance and retreat of the tides
But the moon has
more than a daily cycle
Each month it waxes and wanes
as it travels around the earth,
and this monthly cycle also
triggers events in the ocean
The Pacific Coast of Costa Rica
on a very special night
It just after midnight
and the tide is coming in
The moon is in its last quarter,
exactly half way between full and new
For weeks the beach has been empty
But that is about to change
At high tide,
turtles start to emerge from the surf
At first they come in ones and twos,
but within a hour,
they are appearing all along the beach
They are all female Ridley turtles
and over the next six days or so
four hundred thousand
will visit this one beach
to lay their eggs in the sand
At the peak time, five thousand
are coming and going every hour
The top of the beach gets so crowded that
they have to clamber over one
another to find a bare patch
where they can dig a nest hole
A quarter of the world population
of Ridley turtles come to this one beach
on a few key nights each year
The rest of the time, they are widely
distributed through the ocean
searching for food, most
-a hundreds of miles away from here
This mass nesting is called an arribada
How it is co-ordinated is a mystery
- but we do know that's arribadas start
when the moon is either in its first
or its last quarter
Forty million eggs
are laid in just a few days
By synchronising their nesting in this way
the females ensure that six weeks later
their hatchlings
will emerge in such enormous...
numbers that predators on the beach
are overwhelmed
and a significant proportion
of the baby turtles will get past them
and make it to the water
But why do the females
use a cue from the moon
to help in synchronising their nesting?
Part of the answer to that becomes clear
at dawn on the following morning
The day shift of predators are arriving
for their first meals
Vultures have learnt
that the returning tide
can wash freshly laid eggs out of the sand
The risk of eggs being exposed by the surf
may be part of the reason
why turtle arribadas
tend to occur around the last
or first quarter of the moon
It's on such days as this,
when the moon is neither full nor new,
that the tides are weakest and
the sea is likely to be calmer
So at these times,
it easier for the female turtles
to make their way through the surf
and there less chance of their eggs
being washed out of the sand
and being taken by the vultures
The moon monthly cycle
and its influence on the tides triggers
many events in the ocean,
from the spawning of the corals
on the Great Barrier reef
to the breeding cycles of fish
But there an even longer rhythm
that has the most profound effect of all
- the annual cycle of the sun
The sun position relative
to the earth changes
through the year and
it this that produces the seasons
In the north, spring comes as the sun
begins to rise higher in the sky
Off the coast of North West America,
the seas are transformed by the increasing
strength of the sunshine
Here in Alaska the coastal waters turn
green with a sudden bloom of phytoplankton
Herring that have spent
the winter far out to sea,
time their return to the shallow waters
to coincide with this bloom
They come in vast numbers and initiate
one of the most productive
food chains in all the oceans
Humpback whales are at the top
of that food chain
They have spent the winter breeding
in the warmer tropical waters off Hawaii
But there was little food for them there
This herring bonanza provides the vast
majority of their food for the year
Stellar and Californian sea lions
also return from the open ocean
each year to feast off the herring
The herring themselves,
however, have not come here for food
They are about to breed
Nothing deters them as they head
for even shallower waters
Now the waters
are so shallow that glaucous
-winged gulls are able to snatch live fish
from just below the surface
In spite of these attacks and losses,
the herring swim on until
they reach the vegetation that the females
need if they are to lay
Each female produces
around twenty thousand eggs
- and they every sticky
The males arrive soon after the females
have spawned and release their sperm
in vast milky clouds
Soon the excesses
of the herrings' sexual spree
creates a thick, white scum on the surface
Through the season curds of sperm clog
the shores for hundreds of miles,
from British Columbia in the South
all the way to Alaska in the north
After a few days this gigantic spawning
comes to an end and the herring head
back out to deeper waters,
leaving behind them
fertilised eggs plastered...
on every rock and strand of vegetation
They time their spawning
so that two weeks later,
when these eggs start to hatch,
the annual plankton bloom
will have reached
its height and the new-born fish fry
will have plenty to eat
But in the meantime,
all these eggs provide food
for armies of different animals both below
and above the surface
Millions of birds arrive to collect
a share of the herring bounty
Some of it is easily gathered,
for millions of eggs have been
washed up onto the shore
This encapsulated energy is particularly
valuable to migrating birds
These surfbirds are on their way
to their breeding grounds in the Arctic
and they have to come down to refuel
Stranded herring eggs
are just what they need
Bonaparte gulls collect the eggs
just below the surface of the water
Further out in the bay,
huge flocks of ducks have gathered
They are mostly surf scoters
- diving ducks - that can feed off
the bottom several metres down
There are such huge quantities of eggs
that even such a big animal as a bear
finds it worthwhile to collect them
The spawning of the herring
is a crucial event
in the lives of many animals
all along the coast
The whole event coincides
with the plankton bloom
and within just three short weeks
it all over
The migratory birds leave
to continue their journey north
They will not come back until
the herring also return next year
As the herring spawning finishes,
other migrants are starting
to arrive just offshore
Grey whales
They have followed the sun north
and they too are seeking the food
that is generated by
the bloom of the phytoplankton
Krill are feeding off it and these
whales are feeding on the krill,
skimming it from the surface
with the filter plates of baleen
that hang from their upper jaws
Grey whales make one
of the longest migrations
undertaken by any marine mammal
- a round trip of 12,000 miles or
so from their breeding grounds off Mexico
along the entire coast of North America
right up to the Arctic ocean
They travel close to the coast
with the males
and non-breeding females leading the way
The last to start are the cows
that have just given birth
They have to wait until
their new-born calves
are sufficiently big and strong to tackle
such an immense journey
Their progress is necessarily slow
The mothers must stay
alongside their young
and even a strong calf can only travel
at a couple of knots
They stick even closer to the shore
often within just 200 metres
Killer whales.
They have learnt that grey whales
follow traditional routes
The killers have no trouble in overtaking
a calf and its devoted mother
Normally,
they continually call to one another,
but now they have fallen silent
The mother grey whale and her calf
have no idea that they have been targeted
Catching up with the grey whales
is the easy part for the killers
They have to be cautious
for they are only...
about half the size
of the grey whale mother
She can inflict real damage with her tail
But the killers are not after her
They are after her calf
As long as the mother
can keep it on the move,
it will be safe and
she does her best to hurry it along
At first the killers
avoid getting too close...
to the mother but just keep pace alongside
They know that the calf,
going at this speed, will eventually tire
After three hours
of being harried in this way
the calf becomes too exhausted
to swim any further
The mother has to stop
This is the moment the killers
have been waiting for
They start to try and force themselves
between mother and calf
A calf, separated from its mother,
will not be able to defend itself
Time and again the black fins
of the killers appear between
the mottled backs of the grey whales
At last the killers succeed
And now that they've got the calf
on its own, they change their tactics
They leap right on to the calf
and try to push it under
They are trying to drown it
The calf snatches a desperate breath
The mother becomes increasingly agitated
Frantically,
she tries to push her calf back
to the surface so that it can breathe
But now it is so exhausted that it has
to be supported by its mother's body
The killers won't give up
Like a pack of wolves,
they take turns in harassing the whales
Now the whole pod is involved
One of them takes a bite
Soon the sea is reddened
with the calf's blood
and the killers close in for the final act
The calf is dead
After a six-hour hunt, the killer whales
have finally won their prize
The mother, bereft, has to continue
her migration north on her own
She leaves behind the carcass
of a calf that
she cherished
for thirteen months in her womb
for which she delayed
her own journey to find food
The pod of fifteen killer whales spent
over six hours trying to kill this calf
But now, having succeeded,
they have eaten nothing
more than its lower jaw and its tongue
Valuable food like this will not
go to waste in the ocean
Before long the carcass will sink
to the very bottom of this deep sea
But even there,
its flesh will not be wasted
Over a mile down in the
total darkness of the deep ocean
- the body of another grey whale,
a thirty ton adult
It settled here only a few weeks ago
Already,
it has attracted hundreds of hagfish
These scavengers, over half a metre long
and as thick as your arm,
are only found in the deep sea
They have been attracted
by the faint whiff of
decay suffusing through the water
for miles around
With their heads buried
in the whale's flesh,
they breathe through gill openings
along the sides of their bodies
They're very primitive creatures
- not even true fish, for they lack jaws.
- They feed, not by biting, but by
rasping off flesh
with two rows of horny teeth
In just a few hours,
a hagfish can eat several times
its own weight of rotting flesh
Next to arrive - a sleeper shark
It moves so slowly to conserve energy
- an important strategy for so large
an animal surviving in such a poor habitat
Sleeper sharks live over a mile down
and grow to over seven metres long
They can go for months without food,
slowly cruising along the bottom,
waiting for rare bonanzas,
such as this one, to arrive from above
A whole range of different
deep-sea scavengers
will feast on this carcass for a long time
before all its nutriment has been consumed
Eighteen months later, all that is left
is a perfect skeleton, stripped bare
The sun's energy that was captured
and turned into living tissue
by the floating
phytoplankton has been transferred from
one link to another in the food chain
and has ended up as far away from the sun
as it is possible to be on this planet
- at the bottom of the deep sea
But some energy also returns from the deep
Millions of opalescent squid are
on their way to the shallows
They have come up here to mate
As the males grab the females,
their tentacles flush red
For most of the year these squid
live at a depth of around 500 metres
They only come together in these great
breeding schools for a few weeks
Just one school was estimated to contain
animals that weigh around 4000 tonnes
Wave after wave rise from the depths
and soon the seabed
in the shallows is strewn
with dense patches of egg capsules
several metres across
As each female adds
another capsule to the pile
the males fight to fertilise its contents
The squid make their huge journey
into the shallows because their eggs
will develop faster
in the warmer water here
and when the young emerge,
they will find more
food more easily than
they would in the ocean depths
Dawn the next morning and the seabed for
miles around is covered in egg capsules.
The squid themselves have all gone
Many will have died, but some will have
returned to their home in the deep
They will not return
to the light of the sun
until the next time they are driven up
by the urge to spawn