Nature's Great Events s01e04 Episode Script

DAVID ATTENBOROUGH: The power of the sun drives the seasons, transforming our planet.
Vast movements of ocean and air currents bring dramatic change throughout the year.
And in a few special places, these seasonal changes create some of the greatest wildlife spectacles on Earth.
The most dramatic event in the world's oceans happens off the eastern shores of South Africa.
These cool waters create the perfect conditions for a spectacle of epic proportions.
And everything revolves around the humble sardine.
Each year millions of them are swept up Africa's coast on a desperate winter journey.
Following them comes what will become the biggest army of predators anywhere on the planet.
The climax to this chase depends on many crucial elements coming together for one brief moment in time.
This can well claim to be the greatest ''shoal'' on Earth.
In the deep water off the southern tip of Africa lie the rich fishing grounds of the Agulhas Bank.
It's home to billions of sardines.
They live in immense shoals as defence against their many predators.
Moving together as one in a shoal gives an individual sardine its best chance of survival.
Sardines are so numerous, they're on the menu of most fish-eating predators here.
It's summer, and the sardines are lost in the vastness of the ocean.
The shoals are so dispersed they're hard to find.
Common dolphins are specialist sardine hunters.
Dolphins aren't the only ones on their trail.
Gannets also rely on a diet of sardines.
The best way for them to find the shoals is to follow the dolphins.
When the fish are far out to sea, the dolphins need great perseverance to track them down.
The dolphins use their own form of sonar, sending out a stream of clicks and whistles, listening for returning echoes.
(CLICKING) At last they've found what they're looking for.
Working as a team, the dolphins isolate a group of fish and corral them into a tight ball close to the surface.
The gannets can now make their move.
Gannets can't dive deep, so they must rely on dolphins to keep the sardines near the surface.
The feeding frenzy is short-lived.
Most of the shoal escapes to the deep and the hunters are left still hungry.
It's December, the height of the southern summer, and the sardines have the advantage.
With the shoals dispersed, life is hard for all the predators.
But in six months' time, if conditions are right, the scene will be set for astonishing and sustained drama.
For a few short weeks each winter, cold ocean currents can sweep great shoals of sardines up the coast.
Trapped close to shore within this corridor of cool water, the fish are vulnerable and their predators will follow in droves.
If it happens, this will be the Sardine Run, one of nature's great events, unique to these shores of South Africa.
But for this epic event to take place, many elements have to come together, and with our changing climate they're less predictable every year.
For the predators, the winter Sardine Run, if it happens, can make the difference between life and death.
Dolphins rely on the easy hunting during the run to wean their calves.
But the omens aren't good.
Last year the sardines didn't run at all.
Gannets follow the same pattern.
They have their chicks in summer, so they, too, leave the nest in time for the Sardine Run.
This is Bird Island, just off the Eastern Cape, the biggest gannet colony in the world.
No less than 1 00,000 breeding pairs come here every summer to have their young.
These incredible numbers show the wealth of life the annual Sardine Run can support.
They also show how many lives may be in jeopardy if the sardines don't run.
Right now the African summer is taking its toll.
With temperatures soaring and no cover on these exposed islands, the birds are in danger of overheating.
The young are especially vulnerable.
They have to be fed every day.
Even with both parents taking turns, it's an exhausting task.
In summer the sardines are a long way out to sea.
The birds fly hundreds of miles in search of a meal.
Once they've sighted their target, they plunge from heights of 30 metres striking the water at 60 mph.
Every dive subjects them to enormous forces.
The slightest miscalculation could be fatal.
Gannets dive no deeper than 1 0 metres, so once again they rely on the dolphins to keep their prey near the surface.
But with so much traffic, there's always the danger of a collision.
This one has broken her neck.
Her death will mean that back on the colony her chick will probably starve.
The rest make the long flight home with their catch.
One partner stays on the island to guard their chick.
The pair welcome each other with a ritualised greeting.
They have a strong bond and many couples mate for life.
During the hours of daylight the sardines stay deep in an attempt to avoid their predators.
As the sun sets, the little fish themselves can begin to feed.
They swim upwards to sieve the water for plankton, microscopic plants and animals.
At daybreak they sink once more into the safety of the deep.
It's not just dolphins and gannets that rely on sardines.
There are other, more mysterious predators.
The Bryde's whale hardly breaks the surface to breathe and never so much as shows a tail fluke.
For a 1 5-metre whale, they can vanish with remarkable ease.
We know little about these stealthy leviathans, other than that they are sardine-hunters, too.
Summer is a lean time for the Bryde's whale, as it is for all the predators.
Sharks follow the same patterns, tracking the shoals offshore through the summer, waiting for the winter Sardine Run when the hunting will be easier.
But being cold-blooded, they don't have the high energy demands of the whales, dolphins and gannets.
All the predators have to endure the lean months, relying on the southern winter in June to bring a change in their fortunes.
Now the changing seasons create a switch in the ocean currents.
As summer gives way to autumn, the southerly-flowing warm current weakens and cold Antarctic water pushes further north, nearer to land.
The sardines are carried along by these cool waters and pushed closer to shore.
If these ocean currents continue to change, the Sardine Run should be only three months away.
It's time for the gannet chicks to leave the safety of their colony.
Parents stop feeding their young when they're three months old.
This forces the chicks to take to the sea.
The young have enough fat reserves to survive for just 1 0 days.
And in this brief window, they must learn how to fly and hunt for themselves.
This is the most critical time in a gannet's life.
Failure will mean starvation.
To prepare for their maiden flight, they test their wings and strengthen their flying muscles.
Eventually, hunger drives them onwards and upwards.
Some get up and away first time.
But many don't make it past the crashing surf.
Some bedraggled chicks struggle back to shore.
But for others, the pounding has been too much.
Fewer than half of all the chicks on this colony survive their first three months of life.
The coast of South Africa is an unforgiving place.
The baby dolphins are still dependent on their mothers.
They suckle for six months before they, like the young gannets, have to start fishing for themselves.
There is such an abundance of fish during the Sardine Run, that even the calves can catch some and so begin to learn their hunting skills.
But the Sardine Run might not even happen this year.
For now the dolphins will have to continue to scour the vast ocean.
Back at the coast, other youngsters are getting ready to go it alone.
Cape fur seals are also waiting for the sardines to come close to shore.
But seals have a broad diet, so they can make the most of other feeding opportunities until the sardines come within range.
Young seals are forced from the colony by the dominant males.
Once they're cast out, the adolescents roam the coastline looking for food.
They won't turn their noses up at a plump young gannet.
Hungry seals patrol the surf, ready to pick off any birds that don't get airborne straight away.
When the wind is light, the gannet chicks are stuck on the island.
Surely they're safe here? But even on land the seal is surprisingly fast on his flippers.
In this one season, on this one colony alone, seals kill up to1 0,000 fledglings.
And, as ever, it all comes down to sardines, for the seals are only after the fish within the stomach of their victims.
For the young birds who do make it past the seals, there are fresh challenges.
Learning the skills of their parents.
First they have to find their quarry, the sardine shoals.
And the best way to do that is to follow the expert trackers.
They're hungry.
It's been days since their parents last fed them.
As the search goes on, the chicks are learning the most sophisticated survival technique of all - how to harness the expertise of another species.
After a long search, the dolphins have found a small school of fish.
They drive the sardines to the surface and within range of the young gannets.
Now, quickly, they have to learn the art of the plunge-dive.
But there's a problem.
The opportunistic seals have found the fish, too.
The young gannets have a daunting choice.
To risk diving with the enemy or to starve.
If they don't take their chances soon, there will be nothing left.
They're in luck.
With sardines back on the menu, the seals ignore the gannets.
As ever, the dolphins have done the hard work of rounding up the fish, and now a host of other predators take advantage.
With the shoal diminishing by the second, competition is fierce.
But there is still time for a mighty intruder.
The Bryde's whale devours the entire ball of fish.
Until the Sardine Run starts in earnest, these minor skirmishes are mere preludes to the main event.
But winter is finally on the way.
The cold current pushes further north.
This cool water forces its way up the coast.
If it continues to flow northwards, it will carry great shoals of sardines with it.
The predators begin to gather, in anticipation of a feast.
Sardines can't tolerate water above 20 degrees centigrade.
So unless the cool water penetrates further up the coast, the fish won't move and the annual run just won't happen.
Perhaps climate change has made its mark here.
The waters have stayed too warm, stalling the movement of fish.
There hasn't been a sardine run for the past two years.
The entire fleet is becalmed.
A winter storm rolls in from the Antarctic, battering the Cape, bringing cold water.
Driven by their hunger, gannets still try to hunt in these dangerous conditions.
In fact, this wild weather is just what all the predators have been waiting for.
For them, it's a perfect storm.
It has pushed a narrow tongue of colder water up the coast.
This chilly current carries wave after wave of sardines with it.
Hemmed in by the land on one side and warm water on the other, the sardines are being drawn into a trap.
Nature is playing a cruel trick on these unfortunate fish, as they'll get no benefit from their mass voyage.
They're slaves to the cold ocean currents.
More than 500 million fish are swimming towards disaster, and yet this is just a tenth of the sardine population.
The run is on.
Ahead, an ambush is being prepared.
As the seas begin to calm, the dolphins relocate the sardine shoals.
As they track up the coast, the pods unite, combining forces.
They form super-pods of incredible numbers, up to 5,000 dolphins in one group.
This is fast becoming one of the biggest groups of predators anywhere on the planet.
The attackers spread out into wide hunting lines, stretching up to a mile across.
Other divisions follow on, as ever tracking the dolphins.
Shadowing them all, the Bryde's whale.
They're all heading in one direction, towards a place known as Waterfall Bluff.
It's an arc in the coastline which interrupts the flow of currents, trapping the water in a swirling eddy.
And the dolphins know that the massive shoals often get caught in this bottleneck.
But these sardines have managed to avoid the trap.
The first shoals have been carried well to the north of Waterfall Bluff, ahead of the dolphin super-pods.
As the cool water is squeezed into an ever thinner band closer to the shore, the shoals are forced up into the shallows.
Only now do we get a real sense of the sheer volume of fish.
This one shoal stretches along the coast for 1 5 miles.
The water is 1 5 metres deep and packed with sardines from top to bottom.
There could be more than 1 00 million fish in this single shoal alone.
As long as the sardines are in such shallow water, they're beyond the reach of the dolphins, who won't follow for fear of stranding.
And the gannets can't risk diving into such shallow water either.
But there are hunters who can follow.
And they've arrived in their thousands.
Sharks.
Dusky, copper and ragged-tooth sharks encircle the sardines.
But for the little fish, there's safety in such vast numbers.
The sheer volume of sardines, the way they twist and turn in harmony, confuses the sharks.
Without dolphins to round up the fish, these sharks have to find their own solution.
They try to trap the fish against the water's surface.
But this boiling water is mostly sardines escaping.
Few are actually eaten.
Tiny fish triumph over the marauding sharks.
The sharks continue to harry the shoal, pushing it ever northwards.
Back at Waterfall Bluff, the dolphins and gannets are waiting for the next pulse of sardines to come up from the south.
If there is another shoal, this kink in the coastline is the perfect place to ambush them.
But if the fish don't come, these hungry predators face a long journey all the way back to the Cape.
To the north, the survivors of the shark attack are nearing the end of their run at the beaches around Durban.
These seem like the lucky ones.
On their epic journey they've evaded an army of hunters.
But one final, unexpected predator lies in wait.
Fishermen can only net the sardines once they've swum this far north, within easy reach of the shore.
Last year no sardines were seen on this coast.
So far this winter, the fishermen have landed only 50 tonnes, barely a tenth of what they'd expect in a good year.
That's how unpredictable the Sardine Run has become.
After such a long and hazardous voyage, it's a sad end for these sardines.
At Waterfall Bluff, the dolphins and gannets have had to bide their time.
After missing the first shoal, these predators are relying on the currents to sweep another big pulse of sardines up the coast.
Now another great shoal is on the way.
And it's heading straight for Waterfall Bluff.
Trapped between the shore on one side and the warm water on the other, these fish are swimming straight towards the enemy.
The sardines fall back on their instinctive defence, swarming into a huge mass that confuses a predator.
But the dolphins have a strategy that turns this to their advantage.
Working together, they separate off a pocket of sardines.
In smaller numbers the fishes shoaling defence now works against them.
The dolphins corral the bait ball and herd it to the surface.
This is what the other hunters have been waiting for.
Now the sardines are within range of the gannets.
The bait balls form and reform, seldom lasting longer than a few minutes each.
The sharks pile in, taking advantage of the dolphins' hard work.
The predators ignore each other.
There's only one victim here - the millions of tasty little fish they've been stalking for so long.
Young gannets join the frenzy.
In just six months they have become superb aerial hunters.
Time after time, the dolphins round up another shoal for destruction.
Frantically, the little fish try to get away from the seething surface of the water to dive beyond the range of the gannets.
Now, something truly astonishing happens.
Diving takes the gannets down to 1 0 metres.
Then the aerial squadrons become shoals of swimmers as they pursue the fish down to 20 metres.
Sardines join with their predators in a beautiful yet macabre underwater ballet.
There's little chance of escape for these fish.
The stage is set for the biggest predator of all.
The Bryde's whale takes in 1 0,000 fish in one giant mouthful.
But this time around, there are plenty of sardines for all.
Each hunter amongst these millions plays its part in the drama and each is dependent upon the other.
The annual spectacle of the Sardine Run is undoubtedly the greatest gathering of predators anywhere on the planet.
It's surely one of nature's great events.
Then, almost as quickly as it began, it's over.
As the brief winter comes to an end, warm currents flowing south displace the corridor of cool water.
Despite the massacre, more than half of all the sardines swept up on the great run, survive.
As the currents switch, the fortunate ones make good their escape.
From here, they'll follow deep water currents, hitching a ride back to the cool waters of the Cape.
The Bryde's whale melts away to resume its secretive life somewhere out in the big blue.
The dolphin super-pods break up and begin their long trek back to the Cape.
Gannets, too, head south.
As Waterfall Bluff falls quiet once more, no one can say whether this spectacular event will be repeated here in years to come.
The Sardine Run may be unique to the coast of South Africa, but it's a vivid reminder of the riches that our oceans can still support.
The amazing bait balls that characterise the Sardine Run are short-lived and very hard to find.
Filming them was to turn into a two-year mission for the underwater team.
To film the feeding frenzies, the team would need three key elements to come together - a huge shoal of sardines, the right mix of predators and water clear enough to be able to see the action.
The most important element to start with was being able to see underwater.
And at the beginning of the first the season it wasn't looking good for underwater cameraman Didier Noirot.
It looks like dirty water, but I'm going to check anyway to be sure.
ATTENBOROUGH: Didier was Jacques Cousteau's underwater cameraman for more than a decade.
He knows that the Sardine Run is very unpredictable and that some years it never happens at all.
The predators were gathering, but the ocean currents weren't bringing any sardines.
It wasn't a good start to the first season's filming.
MAN: What's it like? No vis.
No visibility.
ATTENBOROUGH: And the murky water held further risks.
Poor vis you don't see what's coming, so it's not that we're scared of all the sharks, but we notice that accidents, people get bitten always in dirty water.
So why should we take the risk? We go in dirty water to make bad pictures and get bitten by sharks.
It's not worth.
I'd rather stay dry! ATTENBOROUGH: After 20 days at sea with no sign of sardines, the crew kept themselves busy with some sound recording for the film.
I didn't take my mask, you see, so I don't intend to dive.
ATTENBOROUGH: The team developed some ingenious techniques to get microphones close to the dolphins and gannets that were also waiting for the sardines.
So what we're doing today is trying a radio mic and a Frenchman.
The problem is he doesn't know when to stop talking.
It's the quietest we've had him for days, but he still rabbits on.
ATTENBOROUGH: No one was prepared for what happened next.
The thing is these aren't waterproof at all.
-Shark, shark! Quick, quick! -Go, go! Quick, quick! He bit me.
Big copper.
It's late, it's murky water.
We cannot stay there too long, you see.
-Did he come right underneath you? -No, he bit my fins.
I kick.
-Seriously? -Yeah, I told you there are sharks, so come and fetch me.
ATTENBOROUGH: The sharks were definitely about, but the first season ended without Didier seeing any sardines.
At the beginning of the second year the pressure was on.
But things were looking up.
With the help of aerial spotter Eric Webber, Didier and the team could search a greater stretch of ocean.
For the first time in three years, a huge slick of fish had been swept up the coast.
The Sardine Run was well and truly on.
And it was down to the eye in the sky to get Didier into the heart of the action.
We've got thousands of sharks approximately 200 metres offshore.
You guys make your way out there, you'll be mad enough to go into the water.
I'll talk you onto it, guys.
It's really looking good.
It's just sharks and sards all over the place.
We are in the area.
Didier wants us to deploy on the highest concentration of sharks.
Would you please guide us onto that area.
Come 20 degrees left, you've got 40 metres to run.
40 metres to run.
I'm going to put you in the front of the sards.
Seconds to run, divers ready.
Nine, eight, seven, six, five Divers ready.
Four, three, two, one.
Go! Divers away.
ATTENBOROUGH: The great tide was indeed living up to its name.
At last Didier had some action to film.
He had good visibility and sardines in abundance.
But without dolphins around, the feeding frenzies just weren't happening.
The sharks were unable to feed on the vast walls of fish and despite their impressive numbers, they were surprisingly wary of Didier.
No, very quiet, moving slowly.
They are the lords of the sea.
No, there was no frenzy, no attack.
I think they get prepared for the big action.
ATTENBOROUGH: Didier had yet to even see a big bait ball and there was only one week left for all the elements to come together - clean water, lots of sardines, and just the right mix of predators.
And if there was one place to find it, it was Waterfall Bluff.
Huge numbers of predators were starting to gather.
This was the most action the underwater crew had seen in two years, and again it was down to Eric to put them on it.
ERIC: This is Raven.
Yeah, we've got some major activity here just off Mkambati.
ATTENBOROUGH: They were into the last week of filming and the pressure was showing.
Yeah, this looks very, very good.
At two o'clock, just here, but it's moving quite fast.
MAN: 'Cause the dolphins are chasing it.
ERIC: Make a slow 90.
Go right 90 degrees.
The tricky part is actually getting us onto the bait ball without breaking it up.
Ridden over the bait ball.
Just stop.
ERIC: Joker, I think you've screwed that up.
Too far! Don't get there.
Move the boat, to the right! -Below Eric.
Below Eric.
Where's Eric? -We should go outside there.
Now we have to go fast and to think fast! ATTENBOROUGH: On the second-to-last day of filming, Didier finally got his chance.
Okay, Didier.
ATTENBOROUGH: Years of work had gone into putting Didier on the front line.
Now it was down to him.
After 90 days of filming, he had less than an hour in which to fulfil his dream - to film a bait ball in perfect conditions.
Didier was at last amongst the greatest gathering of predators on the planet.
He'd managed to get closer than anyone to the feeding frenzy, without becoming part of it.
Ah! Today was the day.
We just found a bait ball.
We were looking for months, years, and we finally found it.
Only one problem.
The sharks were too much aggressive.
We were very We got bumped a few times by sharks, and that was just a bit serious.
All that action came and that was just an amazing spectacle.
All those birds diving together.
Bom, bom, bom.
Boom, boom.
Like real cannon explosion.
And all those sharks under, following.
And the dolphins.
That was just magical.
Magical.
ATTENBOROUGH: The feeding frenzy they filmed that day ended as quickly as it had begun.
After two long years, Didier and the crew had managed to be in just the right place at just the right time for one of our ocean's greatest events.