Nature (1982–…): Season 40, Episode 9 - The Ocean's Greatest Feast - full transcript
South Africa's annual summer sardine migration sees billions of sardines traveling up the coast.
Alone, a single fish
may be insignificant.
But together, they can hold
the fate of an entire coastline.
In the deep,
billions of sardines
begin a mass migration...
Sparked by a whisper
of cool water.
It's the largest movement
of living things on Earth.
And it's about to become
nature's greatest ambush.
Every predator along the coast
is counting on this event...
...to feast on the abundance
the sardines bring...
...before they slip away
into the deep.
Off the southern tip of Africa,
the frigid South Atlantic mixes
with the milder Indian ocean.
The waters are cold and rich
with plankton,
fed by upwellings
from the mighty Atlantic.
Perfect conditions
for a tiny fish to thrive.
Sardines by the billions
live here year-round,
swimming and feeding together
in loose shoals
of hundreds of thousands
of individuals.
Then in late April, ocean
currents undergo a subtle shift.
As the southern winter
approaches,
upwellings and eddies force
a tendril of cold water
toward the east.
The warm Agulhas Current
moves further offshore,
allowing the cold stream
to gain momentum.
The cold-water sardines
instinctively cluster
in the chillier current.
150 miles out to sea,
on the Agulhas Banks,
schools begin to mass
together...
...until they form a mega shoal
20 miles long.
Then the single superorganism
pours
into the cold-water highway
toward the coast
and shallower water.
It's the biggest biomass
migration on the planet,
exceeding the great herds
of the Serengeti.
Yet, exactly why they do it
remains a mystery.
The journey serves no apparent
benefit to the fish.
It will inevitably dead-end
in a warm sea,
unsuitable for sardines.
How far they travel
depends entirely on the vagaries
of this year's cold current.
But one thing is certain...
an entire food web is counting
on the sardines to make the run.
Some predators will follow
the shoal for weeks.
Others wait for the feast
to pass close to shore.
Some even race hundreds of miles
to intercept it.
To the multitude, this year's
sardine run can mean
the difference between
abundance and deprivation.
All are at the mercy
of the current.
If the water temperature
stays below 70 degrees,
the sardines could travel
1,000 miles
up the Eastern coast
of South Africa.
But if the tendril
of cold water fades,
the shoals will turn, disperse,
or disappear into the deep.
The coastline waits.
The first hazard for the fish
lies just 100 miles
from the sardine's home turf...
...a colony of some 4,000
Cape fur seals.
They're local predators,
patrolling the shallows
close to shore.
The pups need milk
every four hours...
...so moms can't go far to hunt.
And they're reluctant to leave
the safety
of coastal kelp forests.
The towering plants
offer protection
from great white sharks.
If the seals are to feast
on sardines,
they need the shoals
to come to them.
Mothers depend on the oily fish
to fuel their milk supply.
And they're already pregnant
with next year's baby...
...a precarious position
when your food source is fickle.
The colony is crowded.
Pups cling to mothers.
Tempers fray.
But this year, the sea delivers.
The cold current pushes clouds
of zooplankton
toward the coast
and the seal colony.
The little fish
follow their food...
...directly into the kelp beds.
For the seals,
it's the moment of the year.
Their front flippers are large
and incredibly powerful.
Like paddles, they propel
the seals at 15 miles per hour.
And they provide control when
maneuverability matters most.
Every seal cooperates.
The seals swallow fish whole...
...even when they're underwater.
In the onslaught, the sardines
school in an ever tighter mass.
It's a proven defense.
Every fish is equipped
with a lateral line...
sensory cells in its head,
trunk, and tail.
It's sensitive enough to pick up
the slightest change
in water pressure.
When a fish feels
its neighbor move,
it instantly responds in kind.
Millions of tiny, synchronized
movements combine into one,
forming a superorganism
that shape-shifts
and slips just out of reach.
The assault by thousands
of hungry seals
barely makes a dent
in the giant shoal.
The sardines make their getaway
up the coast,
and the seals don't follow.
They need to get back
to their hungry pups.
The shoal always stays
in the cold current,
covering up to 40 miles a day.
Now the females drop eggs
as they move up the coast...
...prompting some to suggest
that this is
an annual spawning run.
Others say it's simply
driven by wind and cold water.
With each mile, the water grows
imperceptibly warmer.
There's no telling
where or when,
but the cold current
will eventually dissipate.
For now, it remains strong,
impelling the fish onward.
By early May, the sardines
approach another landmark...
400 miles east
of the seal colony.
Bird Island.
It's the world's biggest colony
of Cape gannets.
For three months,
the birds have been
feeding their growing chicks.
They may be fierce
ocean predators,
but they're also
devoted parents.
They're monogamous,
always returning
to the same nest.
It's crowded.
That means competition
for real estate...
and food.
With over 200,000 birds
in the colony,
they need 9,000 tons of fish
in one breeding season.
The gannets have pinned
their entire breeding cycle
on the unpredictable
arrival of sardines.
Scouts return with full bellies
and good news.
The fish are coming.
The sardine superorganism
is 20 miles offshore...
...within striking distance
of the colony.
The birds appear awkward
on the ground, even comical.
But once they achieve air speed,
they are all grace and danger.
They soar 100 feet in the air.
They scan the shoal
with binocular vision...
...lock on to a target...
then dive.
Gannets hit the water
at 60 miles per hour.
Muscles lock their
neck vertebrae into place.
Airbags in the face and chest
absorb impact.
The sardines swim deeper
to escape,
but the birds' momentum
carries them down...
...30 feet underwater.
If a gannet misses the target,
it holds its breath
and paddles, penguin-like,
for a second grab.
This first hunt is all
for the youngsters.
Gannet parents load up
their gizzards
and return at high speed
to Bird Island.
Every parent knows
exactly where to find its chick.
The food cargo is precious.
A healthy sardine run
means more young gannets
are given a chance to survive.
But
is the fledglings'
last free meal.
this
The parent birds will leave them
forever and follow the shoals.
Any gannet that wants to eat
must get on the wing
and follow the fish.
This is motivation
for the chicks to fly.
The hungrier they get,
the harder they try.
The learning curve is steep,
against howling wind
and rough seas.
Crash-landing in the waves
is their first pitfall...
but the wild surf
is not the real danger.
Fur seals hunt
these shores, too.
Fledglings don't have
the strength or experience
for a water take-off.
Soaked feathers weigh them down.
Just as the gannets exacted
their toll on the sardines,
the bird colony
now suffers its own losses.
The lucky ones must dry
their feathers and try again.
They can't miss out on the first
sardine hunt of their lives.
The sardines move east
at 6 miles per hour.
They're approaching the first
real crux of their journey.
600 miles into the run,
the coastline bends north,
and the continental shelf
starts to narrow.
Their cold-water ribbon
is pinched against the coast
by warm offshore currents.
Billions of sardines
must squeeze
into the cold
but narrowing channel.
The shoal is stretched longer
and thinner.
The fish pack tighter together.
This current delivers them to
a place called the Wild Coast.
It's a 200-mile stretch...
A pristine, untouched transition
between temperate
and tropical biomes.
It's not only a mix
of water temperatures,
it's also a crossroads
for myriad species.
It's June and humpback whales
pass from Antarctica
to breeding grounds
farther north.
Others live here all year round.
50 miles ahead of the shoal,
resident bottlenose dolphins
relish winter's arrival.
Dolphins live in social groups
of about 25 members.
Their play reveals why
they're such formidable hunters.
They're fast, they communicate,
and they move as a unit.
A real-life sardine nemesis.
And this resident pod
is just the advance guard
for an even greater army.
Common dolphins.
They spend most of their lives
in warmer waters
along the coast.
This time of year, their calves
are just beginning to hunt.
Mothers need to wean them before
next spring's breeding season.
A glut of fish would be
a crucial windfall.
There's no guarantee
the sardine run will reach them.
So they come to it.
As they head south, hundreds
of small family pods converge.
A dolphin super pod
begins to form,
streaming to intercept
the shoal.
100 miles to the south, the fish
pour along the Wild Coast...
unaware of what lies ahead.
As the narrowing current
pushes them to the shallows,
the shoal fragments.
Smaller, isolated bait balls
offer a new opportunity...
for sharks.
These migratory blacktips
and dusky sharks
have moved down from
the warmer waters farther north.
Little is known of their lives,
but shark nurseries
have been discovered nearby,
suggesting that the sharks...
Like other creatures
along the coast...
may time their breeding cycle
to the sardine run.
Tiny fish face off
with dozens of sharks.
It seems an unfair match...
but the sardines launch
their schooling defense.
As the sharks move, they send a
pressure wave through the water.
The fish detect it through
their sensitive lateral lines.
Just one moves out
of harm's way,
and every fish
around it follows.
It's incredibly effective.
The sharks simply can't turn
and bite quick enough.
The predators change tactics.
With sudden bursts of speed,
they try and carve the shoal
into even smaller balls...
...but they just don't
coordinate enough.
A school of 60-pound tuna
gets in on the action.
Normally the sharks hunt tuna,
but they seem to know help
when they see it.
The smaller tuna
are much more agile.
Within seconds, they slice
a bait ball from the shoal
and trap it against the surface,
where it's easier
for everyone to feed.
Game fish and sharks
enjoy a temporary truce
as they feast on the same prey.
The main shoal flees north,
leaving this fragment behind
to be obliterated.
Even the gulls get their share.
The mega shoal is now way
out of its home habitat.
As long as it's cold,
they swim blindly along.
They're heading toward a feature
of the South African coast
that will prove the most
consequential milestone
of their journey...
A sandstone buttress
called Waterfall Bluff.
This rocky promontory shoves
the cold current eastward
to collide with the warm water
just offshore.
Some years the cold water
can blast beyond this point...
but not this year.
The vital current thins
to a trickle.
The sardines follow into
the bottleneck as if spellbound.
Every single fish follows
the same mission...
Stick with the school
and stay in the middle.
But in the fading current,
the already fractured shoal
breaks up even further.
Small schools follow shifting
pockets of cool water
into oblivion.
The great journey stalls
for the fish
and conditions align
for every predator.
A familiar enemy has
trailed them all this way.
Some gannets will fly
for 24 hours
to intercept the bottleneck...
and there are plenty more
roosting on the nearby coast.
It's a true test
for the rookies.
The sharks are back
for more, too.
Until now, the sardines
have managed to slough off
small bait balls
as sacrificial decoys.
But now they're more vulnerable
than they've ever been.
The high-flying gannets
are the first to spot
a stalling shoal.
The birds stand out
against the sky
like a homing beacon,
guiding in an army.
It's the dolphin super pod...
...now grown to 20,000 strong.
The sardines now face
an unprecedented assault
from a fleet
of swift ocean-going hunters...
...and a far-flung deadly
air force assembling above.
The sardines turn
to the only defense they know...
Schooling up
as tight as they can.
One moves, and they all move.
But the dolphins are prepared
for this.
Their goal is to prevent
the shoal from diving deep.
They coordinate their efforts,
blocking the sardines' evasion.
With surgical precision,
they slice balls away
from the main shoal.
They blow bubbles to corral any
fish that tries to break form...
...forcing the fish tighter
and tighter together.
Every fish instinctively
tries to get
into the middle of the pack.
But now exhausted gills
struggle to suck oxygen
from turbulent water.
Ball after ball is dissected
from the shoal and obliterated.
The dolphins get
what they've waited for.
The toll is exponential.
The dolphins are so effective
at herding the fish
that every other predator
is also more successful.
As the fish are driven
to the surface,
gannets get easy access.
Dark fledglings now hunt
like experts.
Sharks follow and wait
for the perfect moment
to cash in on the tight balls.
They pick off the edges
at first...
...then they plough in.
The dolphins are relentless.
Youngsters take the cue and feed
on fish for the first time.
Along miles of coastline,
every predator is synchronized.
Unlikely accomplices
of all stripes work together
toward one brutal goal.
And then,
with the fish exhausted
and thousands of predators
well fed,
the biggest arrives...
...a 20-ton Bryde's whale.
Thousands of sardines gone
in a single gulp.
The feast goes on for days.
The great shoal is in tatters.
It's now a 3-mile buffet.
Too confused and spent
to reform their shoal,
they're almost 800 miles
from home.
They've been duped
by the vanishing current.
Now they're lost and scattered
in a strange, warm ocean...
...simply food for others.
And yet it isn't over.
The predator of all predators
arrives.
Orcas.
As smart and cooperative
as a common dolphin
and three times bigger.
Orcas never used to travel
for the sardine run,
but now they swim thousands of
miles to intercept the shoals.
But it's not the sardines
they're after.
They're here to hunt dolphins.
Not chasing anymore but running.
The orcas are not only
more powerful,
they have more stamina.
Just as the dolphins
corralled the fish,
now the orcas work the dolphins.
They isolate one from the pod.
Once they've locked onto
their target, they tag-team...
chasing it...
exhausting it...
then... ramming it.
They attack again and again
until the dolphin
can no longer swim.
Before they can feast,
they drown it.
The orcas have scattered
the dolphin super pod.
Without the organizing force
of the dolphins,
the sardines regroup and
slip away into deep, cold water.
The massive cloud of fish
that dominated the coastline
suddenly vanishes,
as if absorbed by the sea.
As July concludes,
the sated hunters disperse.
Gannets proceed to travel up
to 60 miles a day
searching for more food.
Sharks continue
their migrations,
fully fed and stronger for it.
Dolphins have successfully
weaned their calves.
Super pods thin out
as family units regroup
and return to their
regular hunting grounds.
The cold current has delivered
the feast
that all the animals
were counting on.
Now it fades away, mixing
with the warm Indian Ocean.
Some believe the sardines
ride the current down
to secretly spawn in the deep.
Others say they follow it
all the way back,
1,000 miles
to their home off the Cape.
Next year the cold current
will reform,
stronger or weaker
than the last...
and billions of little fish
will be driven
to follow its call,
to face hardship and sacrifice,
toward a purpose yet unknown.
To learn more
about what you've seen
on this "Nature" program,
may be insignificant.
But together, they can hold
the fate of an entire coastline.
In the deep,
billions of sardines
begin a mass migration...
Sparked by a whisper
of cool water.
It's the largest movement
of living things on Earth.
And it's about to become
nature's greatest ambush.
Every predator along the coast
is counting on this event...
...to feast on the abundance
the sardines bring...
...before they slip away
into the deep.
Off the southern tip of Africa,
the frigid South Atlantic mixes
with the milder Indian ocean.
The waters are cold and rich
with plankton,
fed by upwellings
from the mighty Atlantic.
Perfect conditions
for a tiny fish to thrive.
Sardines by the billions
live here year-round,
swimming and feeding together
in loose shoals
of hundreds of thousands
of individuals.
Then in late April, ocean
currents undergo a subtle shift.
As the southern winter
approaches,
upwellings and eddies force
a tendril of cold water
toward the east.
The warm Agulhas Current
moves further offshore,
allowing the cold stream
to gain momentum.
The cold-water sardines
instinctively cluster
in the chillier current.
150 miles out to sea,
on the Agulhas Banks,
schools begin to mass
together...
...until they form a mega shoal
20 miles long.
Then the single superorganism
pours
into the cold-water highway
toward the coast
and shallower water.
It's the biggest biomass
migration on the planet,
exceeding the great herds
of the Serengeti.
Yet, exactly why they do it
remains a mystery.
The journey serves no apparent
benefit to the fish.
It will inevitably dead-end
in a warm sea,
unsuitable for sardines.
How far they travel
depends entirely on the vagaries
of this year's cold current.
But one thing is certain...
an entire food web is counting
on the sardines to make the run.
Some predators will follow
the shoal for weeks.
Others wait for the feast
to pass close to shore.
Some even race hundreds of miles
to intercept it.
To the multitude, this year's
sardine run can mean
the difference between
abundance and deprivation.
All are at the mercy
of the current.
If the water temperature
stays below 70 degrees,
the sardines could travel
1,000 miles
up the Eastern coast
of South Africa.
But if the tendril
of cold water fades,
the shoals will turn, disperse,
or disappear into the deep.
The coastline waits.
The first hazard for the fish
lies just 100 miles
from the sardine's home turf...
...a colony of some 4,000
Cape fur seals.
They're local predators,
patrolling the shallows
close to shore.
The pups need milk
every four hours...
...so moms can't go far to hunt.
And they're reluctant to leave
the safety
of coastal kelp forests.
The towering plants
offer protection
from great white sharks.
If the seals are to feast
on sardines,
they need the shoals
to come to them.
Mothers depend on the oily fish
to fuel their milk supply.
And they're already pregnant
with next year's baby...
...a precarious position
when your food source is fickle.
The colony is crowded.
Pups cling to mothers.
Tempers fray.
But this year, the sea delivers.
The cold current pushes clouds
of zooplankton
toward the coast
and the seal colony.
The little fish
follow their food...
...directly into the kelp beds.
For the seals,
it's the moment of the year.
Their front flippers are large
and incredibly powerful.
Like paddles, they propel
the seals at 15 miles per hour.
And they provide control when
maneuverability matters most.
Every seal cooperates.
The seals swallow fish whole...
...even when they're underwater.
In the onslaught, the sardines
school in an ever tighter mass.
It's a proven defense.
Every fish is equipped
with a lateral line...
sensory cells in its head,
trunk, and tail.
It's sensitive enough to pick up
the slightest change
in water pressure.
When a fish feels
its neighbor move,
it instantly responds in kind.
Millions of tiny, synchronized
movements combine into one,
forming a superorganism
that shape-shifts
and slips just out of reach.
The assault by thousands
of hungry seals
barely makes a dent
in the giant shoal.
The sardines make their getaway
up the coast,
and the seals don't follow.
They need to get back
to their hungry pups.
The shoal always stays
in the cold current,
covering up to 40 miles a day.
Now the females drop eggs
as they move up the coast...
...prompting some to suggest
that this is
an annual spawning run.
Others say it's simply
driven by wind and cold water.
With each mile, the water grows
imperceptibly warmer.
There's no telling
where or when,
but the cold current
will eventually dissipate.
For now, it remains strong,
impelling the fish onward.
By early May, the sardines
approach another landmark...
400 miles east
of the seal colony.
Bird Island.
It's the world's biggest colony
of Cape gannets.
For three months,
the birds have been
feeding their growing chicks.
They may be fierce
ocean predators,
but they're also
devoted parents.
They're monogamous,
always returning
to the same nest.
It's crowded.
That means competition
for real estate...
and food.
With over 200,000 birds
in the colony,
they need 9,000 tons of fish
in one breeding season.
The gannets have pinned
their entire breeding cycle
on the unpredictable
arrival of sardines.
Scouts return with full bellies
and good news.
The fish are coming.
The sardine superorganism
is 20 miles offshore...
...within striking distance
of the colony.
The birds appear awkward
on the ground, even comical.
But once they achieve air speed,
they are all grace and danger.
They soar 100 feet in the air.
They scan the shoal
with binocular vision...
...lock on to a target...
then dive.
Gannets hit the water
at 60 miles per hour.
Muscles lock their
neck vertebrae into place.
Airbags in the face and chest
absorb impact.
The sardines swim deeper
to escape,
but the birds' momentum
carries them down...
...30 feet underwater.
If a gannet misses the target,
it holds its breath
and paddles, penguin-like,
for a second grab.
This first hunt is all
for the youngsters.
Gannet parents load up
their gizzards
and return at high speed
to Bird Island.
Every parent knows
exactly where to find its chick.
The food cargo is precious.
A healthy sardine run
means more young gannets
are given a chance to survive.
But
is the fledglings'
last free meal.
this
The parent birds will leave them
forever and follow the shoals.
Any gannet that wants to eat
must get on the wing
and follow the fish.
This is motivation
for the chicks to fly.
The hungrier they get,
the harder they try.
The learning curve is steep,
against howling wind
and rough seas.
Crash-landing in the waves
is their first pitfall...
but the wild surf
is not the real danger.
Fur seals hunt
these shores, too.
Fledglings don't have
the strength or experience
for a water take-off.
Soaked feathers weigh them down.
Just as the gannets exacted
their toll on the sardines,
the bird colony
now suffers its own losses.
The lucky ones must dry
their feathers and try again.
They can't miss out on the first
sardine hunt of their lives.
The sardines move east
at 6 miles per hour.
They're approaching the first
real crux of their journey.
600 miles into the run,
the coastline bends north,
and the continental shelf
starts to narrow.
Their cold-water ribbon
is pinched against the coast
by warm offshore currents.
Billions of sardines
must squeeze
into the cold
but narrowing channel.
The shoal is stretched longer
and thinner.
The fish pack tighter together.
This current delivers them to
a place called the Wild Coast.
It's a 200-mile stretch...
A pristine, untouched transition
between temperate
and tropical biomes.
It's not only a mix
of water temperatures,
it's also a crossroads
for myriad species.
It's June and humpback whales
pass from Antarctica
to breeding grounds
farther north.
Others live here all year round.
50 miles ahead of the shoal,
resident bottlenose dolphins
relish winter's arrival.
Dolphins live in social groups
of about 25 members.
Their play reveals why
they're such formidable hunters.
They're fast, they communicate,
and they move as a unit.
A real-life sardine nemesis.
And this resident pod
is just the advance guard
for an even greater army.
Common dolphins.
They spend most of their lives
in warmer waters
along the coast.
This time of year, their calves
are just beginning to hunt.
Mothers need to wean them before
next spring's breeding season.
A glut of fish would be
a crucial windfall.
There's no guarantee
the sardine run will reach them.
So they come to it.
As they head south, hundreds
of small family pods converge.
A dolphin super pod
begins to form,
streaming to intercept
the shoal.
100 miles to the south, the fish
pour along the Wild Coast...
unaware of what lies ahead.
As the narrowing current
pushes them to the shallows,
the shoal fragments.
Smaller, isolated bait balls
offer a new opportunity...
for sharks.
These migratory blacktips
and dusky sharks
have moved down from
the warmer waters farther north.
Little is known of their lives,
but shark nurseries
have been discovered nearby,
suggesting that the sharks...
Like other creatures
along the coast...
may time their breeding cycle
to the sardine run.
Tiny fish face off
with dozens of sharks.
It seems an unfair match...
but the sardines launch
their schooling defense.
As the sharks move, they send a
pressure wave through the water.
The fish detect it through
their sensitive lateral lines.
Just one moves out
of harm's way,
and every fish
around it follows.
It's incredibly effective.
The sharks simply can't turn
and bite quick enough.
The predators change tactics.
With sudden bursts of speed,
they try and carve the shoal
into even smaller balls...
...but they just don't
coordinate enough.
A school of 60-pound tuna
gets in on the action.
Normally the sharks hunt tuna,
but they seem to know help
when they see it.
The smaller tuna
are much more agile.
Within seconds, they slice
a bait ball from the shoal
and trap it against the surface,
where it's easier
for everyone to feed.
Game fish and sharks
enjoy a temporary truce
as they feast on the same prey.
The main shoal flees north,
leaving this fragment behind
to be obliterated.
Even the gulls get their share.
The mega shoal is now way
out of its home habitat.
As long as it's cold,
they swim blindly along.
They're heading toward a feature
of the South African coast
that will prove the most
consequential milestone
of their journey...
A sandstone buttress
called Waterfall Bluff.
This rocky promontory shoves
the cold current eastward
to collide with the warm water
just offshore.
Some years the cold water
can blast beyond this point...
but not this year.
The vital current thins
to a trickle.
The sardines follow into
the bottleneck as if spellbound.
Every single fish follows
the same mission...
Stick with the school
and stay in the middle.
But in the fading current,
the already fractured shoal
breaks up even further.
Small schools follow shifting
pockets of cool water
into oblivion.
The great journey stalls
for the fish
and conditions align
for every predator.
A familiar enemy has
trailed them all this way.
Some gannets will fly
for 24 hours
to intercept the bottleneck...
and there are plenty more
roosting on the nearby coast.
It's a true test
for the rookies.
The sharks are back
for more, too.
Until now, the sardines
have managed to slough off
small bait balls
as sacrificial decoys.
But now they're more vulnerable
than they've ever been.
The high-flying gannets
are the first to spot
a stalling shoal.
The birds stand out
against the sky
like a homing beacon,
guiding in an army.
It's the dolphin super pod...
...now grown to 20,000 strong.
The sardines now face
an unprecedented assault
from a fleet
of swift ocean-going hunters...
...and a far-flung deadly
air force assembling above.
The sardines turn
to the only defense they know...
Schooling up
as tight as they can.
One moves, and they all move.
But the dolphins are prepared
for this.
Their goal is to prevent
the shoal from diving deep.
They coordinate their efforts,
blocking the sardines' evasion.
With surgical precision,
they slice balls away
from the main shoal.
They blow bubbles to corral any
fish that tries to break form...
...forcing the fish tighter
and tighter together.
Every fish instinctively
tries to get
into the middle of the pack.
But now exhausted gills
struggle to suck oxygen
from turbulent water.
Ball after ball is dissected
from the shoal and obliterated.
The dolphins get
what they've waited for.
The toll is exponential.
The dolphins are so effective
at herding the fish
that every other predator
is also more successful.
As the fish are driven
to the surface,
gannets get easy access.
Dark fledglings now hunt
like experts.
Sharks follow and wait
for the perfect moment
to cash in on the tight balls.
They pick off the edges
at first...
...then they plough in.
The dolphins are relentless.
Youngsters take the cue and feed
on fish for the first time.
Along miles of coastline,
every predator is synchronized.
Unlikely accomplices
of all stripes work together
toward one brutal goal.
And then,
with the fish exhausted
and thousands of predators
well fed,
the biggest arrives...
...a 20-ton Bryde's whale.
Thousands of sardines gone
in a single gulp.
The feast goes on for days.
The great shoal is in tatters.
It's now a 3-mile buffet.
Too confused and spent
to reform their shoal,
they're almost 800 miles
from home.
They've been duped
by the vanishing current.
Now they're lost and scattered
in a strange, warm ocean...
...simply food for others.
And yet it isn't over.
The predator of all predators
arrives.
Orcas.
As smart and cooperative
as a common dolphin
and three times bigger.
Orcas never used to travel
for the sardine run,
but now they swim thousands of
miles to intercept the shoals.
But it's not the sardines
they're after.
They're here to hunt dolphins.
Not chasing anymore but running.
The orcas are not only
more powerful,
they have more stamina.
Just as the dolphins
corralled the fish,
now the orcas work the dolphins.
They isolate one from the pod.
Once they've locked onto
their target, they tag-team...
chasing it...
exhausting it...
then... ramming it.
They attack again and again
until the dolphin
can no longer swim.
Before they can feast,
they drown it.
The orcas have scattered
the dolphin super pod.
Without the organizing force
of the dolphins,
the sardines regroup and
slip away into deep, cold water.
The massive cloud of fish
that dominated the coastline
suddenly vanishes,
as if absorbed by the sea.
As July concludes,
the sated hunters disperse.
Gannets proceed to travel up
to 60 miles a day
searching for more food.
Sharks continue
their migrations,
fully fed and stronger for it.
Dolphins have successfully
weaned their calves.
Super pods thin out
as family units regroup
and return to their
regular hunting grounds.
The cold current has delivered
the feast
that all the animals
were counting on.
Now it fades away, mixing
with the warm Indian Ocean.
Some believe the sardines
ride the current down
to secretly spawn in the deep.
Others say they follow it
all the way back,
1,000 miles
to their home off the Cape.
Next year the cold current
will reform,
stronger or weaker
than the last...
and billions of little fish
will be driven
to follow its call,
to face hardship and sacrifice,
toward a purpose yet unknown.
To learn more
about what you've seen
on this "Nature" program,