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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's wings.
its streamlining, close to perfection,
enables it to cruise at 20 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 40 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.
0ur planet is a blue planet.
0ver 70 per cent of it is covered by the sea.
The Pacific 0cean alone covers half the globe.
You can fly across it non-stop for 12 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 per cent of the earth's inhabitable space,
and the sheer quantity of its marine life
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.
0ut 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 seabed.
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 from the sea floor thousands of metres below.
The nearest land is 300 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 plankton - tiny floating plants and animals
nourished by the richness brought up from the depths,
and they 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, Mapelo and the Galapagos,
attract silkies in huge groups up to 500 strong.
Silkies seem to specialise 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 gave many sharks 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 mostly in the cold waters south of the Cape,
but each year the coastal currents reverse.
The warm Agulhas current that flows down from the north
has been displaced by cold water 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 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's 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.
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's whale.
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 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 from the sun is also essential
for the growth of the microscopic floating plants -
the phytoplankton.
And it's 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.
0ne thousand million tonnes 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.
0ther 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 advances and retreats of the tide.
But the moon has more than a daily cycle.
Each month, it waxes and wanes as it travels round the earth,
and this monthly cycle also triggers events in the ocean.
The Pacific coast of Costa Rica
on a very special night.
it's 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 an hour,
they are appearing all along the beach.
They are all female Ridley's turtles,
and over the next six days or so,
400,000 will visit this one beach
to lay their eggs in the sand.
At the peak time, 5,000 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 patch
where they can dig a nest hole.
A quarter of the world's population of Ridley's 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,
most, hundreds of miles away.
This mass nesting is called an arribada. How it's co-ordinated
is a mystery,
but we do know that arribadas start
when the moon is either in its first or last quarter.
Forty million eggs are laid in just a few days.
By synchronising their nesting, the females ensure
that six weeks later, their hatchlings will emerge
in such enormous numbers
that predators are overwhelmed,
and a significant proportion of baby turtles will make it to the water.
But why do the females use a cue from the moon
to help synchronise 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 partly 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 it's easier for the female turtles to make their way through the surf,
and harder for eggs to be washed out of the sand
and taken by vultures.
The moon's 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's an even longer rhythm
that has the most profound effect of all -
the annual cycle of the sun.
The sun's position relative to the earth
changes through the year,
and it's this that produces the seasons.
in the north, spring comes
as the sun begins to rise higher in the sky.
0ff the coast of north west America,
the seas are transformed by the increasing strength of the sun.
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 there.
This herring bonanza
provides the 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, 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
can snatch live fish from just below the surface.
in spite of these attacks, the herring swim on
until they reach the vegetation
that the females need if they are to lay.
Each female produces around 20,000 eggs,
and they're very sticky.
After the females have spawned, the males 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 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 the spawning so that two weeks later, when the eggs hatch,
the annual plankton bloom will be at its height, and the fish fry
will have plenty to eat.
in the meantime, these eggs provide food
for armies of different animals below and above the surface.
Millions of birds arrive to collect a share of the herrings' 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 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're mostly surf scoters -
diving ducks that can feed off the bottom several metres down.
There are such huge quantities of eggs,
that even a big animal like 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 three short weeks, it's 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 offshore.
Grey whales.
They have followed the sun north,
and they too are seeking the food
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
of 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 up to the Arctic 0cean.
They travel close to the coast,
with the males and non-breeding females leading the way.
The last to start are cows that have just given birth.
They have to wait until their calves are sufficiently strong
to tackle such an immense journey.
Their progress is necessarily slow.
The mothers stay with their young,
and even a strong calf only travels 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 the calf and its devoted mother.
Normally, they continually call to one another,
but now they have fallen silent.
The grey whale and her calf
have no idea that they've 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 mother.
She can inflict real damage with her tail.
But the killers 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 but just stay alongside.
They know that the calf, going at this speed, will eventually tire.
After three hours of being harried,
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 grey whales.
At last the killers succeed,
and now they've got the calf on its own,
they change their tactics.
They leap right onto 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's 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.
0ne 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 13 months in her womb,
for which she delayed her own journey to find food.
The 15 killer whales spent over six hours trying to kill the calf,
but having succeeded,
they've 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.
0ver a mile down, in the total darkness of the deep ocean,
the body of another grey whale,
a 30-tonne 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 their sides.
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,
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.
18 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 to another link in the food chain,
and has ended up as far away from the sun as it is possible to be -
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've 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 are part of these breeding schools for a few weeks.
just one school was estimated to contain animals
that weigh around 4,000 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 have all gone. Many 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.
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