- 6/20/2025
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00:00The power of the Sun drives the seasons, transforming our planet.
00:12Vast movements of ocean and air currents bring dramatic change throughout the year.
00:22And in a few special places, these seasonal changes create some of the greatest wildlife spectacles.
00:29On Earth.
00:34The most dramatic event in the world's oceans happens off the eastern shores of South Africa.
00:46These cool waters create the perfect conditions for a spectacle of epic proportions.
00:52And everything revolves around the humble sardine.
01:04Each year, millions of them are swept up Africa's coast on a desperate winter journey.
01:10Following them comes what will become the biggest army of predators anywhere on the planet.
01:20The climax to this chase depends on many crucial elements coming together for one brief moment in time.
01:35This can well claim to be the greatest shoal on Earth.
01:46In the deep water off the southern tip of Africa lie the rich fishing grounds that the
02:03earth accesses.
02:04In the deep water of the southern tip of Africa
02:13lie the rich fishing grounds of the Agoulas Bank.
02:21It's home to billions of sardines.
02:23They live in immense shoals as defence against their many predators.
02:34Moving together as one in a shoal gives an individual sardine
02:39its best chance of survival.
02:45Sardines are so numerous,
02:47they're on the menu of most fish-eating predators here.
02:59It's summer, and the sardines are lost in the vastness of the ocean.
03:03The shoals are so dispersed, they're hard to find.
03:25Common dolphins are specialist sardine hunters.
03:33Dolphins aren't the only ones on their trail.
03:39Dolphins aren't the only ones on their trail.
03:41Gannets also rely on a diet of sardines.
03:47The best way for them to find the shoals is to follow the dolphins.
03:51When the fish are far out to sea,
04:02the dolphins need great perseverance to track them down.
04:13The dolphins use their own form of sonar,
04:16sending out a stream of clicks and whistles,
04:19listening for returning echoes.
04:35At last, they've found what they're looking for.
04:38Working as a team, the dolphins isolate a group of fish
04:52and corral them into a tight ball close to the surface.
05:01The gannets can now make their move.
05:03Gannets can't dive deep, so they must rely on dolphins
05:04to keep the sardines near the surface.
05:26Gannets can't dive deep, so they must rely on dolphins
05:28so they must rely on dolphins to keep the sardines near the surface.
05:45The feeding frenzy is short-lived.
05:47Most of the shoal escapes to the deep,
05:50and the hunters are left still hungry.
05:53It's December, the height of the southern summer,
05:59and the sardines have the advantage.
06:01With the shoals dispersed, life is hard for all the predators.
06:13But in six months' time, if conditions are right,
06:16the scene will be set for astonishing and sustained drama.
06:23For a few short weeks each winter,
06:28cold ocean currents can sweep great shoals of sardines up the coast.
06:35Trapped close to shore within this corridor of cool water,
06:39the fish are vulnerable and their predators will follow in droves.
06:46If it happens, this will be the sardine run,
06:49one of nature's great events, unique to these shores of South Africa.
06:56But for this epic event to take place,
06:59many elements have to come together.
07:01And with our changing climate,
07:03they're less predictable every year.
07:08For the predators, the winter sardine run, if it happens,
07:12can make the difference between life and death.
07:15Dolphins rely on the easy hunting during the run to wean their calves.
07:22But the omens aren't good.
07:24Last year, the sardines didn't run at all.
07:32Gannets follow the same pattern.
07:34They have their chicks in summer,
07:36so they too leave the nest in time for the sardine run.
07:39This is Bird Island, just off the Eastern Cape,
07:54the biggest gannet colony in the world.
07:57No less than 100,000 breeding pairs come here every summer
08:08to have their young.
08:17These incredible numbers show the wealth of life
08:20the annual sardine run can support.
08:27They also show how many lives may be in jeopardy
08:31if the sardines don't run.
08:41Right now, the African summer is taking its toll.
08:44With temperatures soaring and no cover on these exposed islands,
08:48the birds are in danger of overheating.
08:57The young are especially vulnerable.
09:08They have to be fed every day.
09:10Even with both parents taking turns,
09:12it's an exhausting task.
09:27In summer, the sardines are a long way out to sea.
09:45The birds fly hundreds of miles in search of a meal.
09:57Once they've sighted their target, they plunge from heights of 30 metres.
10:10Striking the water at 60 miles an hour.
10:13Every dive subjects them to enormous forces.
10:36The slightest miscalculation could be fatal.
10:43Gannets dive no deeper than 10 metres,
10:48so once again, they rely on the dolphins
10:51to keep their prey near the surface.
10:54But with so much traffic, there's always the danger of a collision.
11:13This one has broken her neck.
11:24Her death will mean that, back on the colony,
11:26her chick will probably starve.
11:33The rest make the long flight home with their catch.
11:38One partner stays on the island to guard their chick.
11:43The pair welcome each other with a ritualised greeting.
11:50They have a strong bond and many couples mate for life.
12:13They have a strong bond and many couples mate for life.
12:15During the hours of daylight,
12:17the sardines stay deep in an attempt to avoid their predators.
12:28As the sun sets, the little fish themselves can begin to feed.
12:35They swim upwards to sieve the water for plankton,
12:38microscopic plants and animals.
12:43They swim upwards to the sea.
12:45They swim upwards to the sea.
12:55At daybreak, they sink once more into the safety of the jeep.
13:00At daybreak, they sink once more into the safety of the jeep.
13:01It's not just dolphins and gannets that rely on sardines.
13:23There are other, more mysterious predators.
13:31The brooder's whale hardly breaks the surface to breathe, and never so much as shows a tail fluke.
13:52For a 15-meter whale, they can vanish with remarkable ease.
13:57We know little about these stealthy leviathans, other than they are sardine hunters, too.
14:17Summer is a lean time for the brooder's whale, as it is for all the predators.
14:25Sharks follow the same patterns, tracking the shoals offshore through the summer, waiting
14:36for the winter sardine run, when the hunting will be easier.
14:43But being cold-blooded, they don't have the high energy demands of the whales, dolphins,
14:48and gannets.
14:57All the predators have to endure the lean months, relying on the southern winter in June
15:03to bring a change in their fortunes.
15:05Now, the changing seasons create a switch in the ocean currents.
15:14As summer gives way to autumn, the southerly flowing warm current weakens,
15:19and cold Antarctic water pushes further north, nearer to land.
15:24The sardines are carried along by these cool waters and pushed closer to shore.
15:37If these ocean currents continue to change, the sardine run should be only three months away.
15:43It's time for the gannet chicks to leave the safety of their colony.
16:02Parents stop feeding their young when they're three months old.
16:06This forces the chicks to take to the sea.
16:12The young have enough fat reserves to survive for just ten days.
16:17And in this brief window, they must learn how to fly and hunt for themselves.
16:26This is the most critical time in a gannet's life.
16:30Failure will mean starvation.
16:36To prepare for their maiden flight, they test their wings and strengthen their flying muscles.
16:51Eventually, hunger drives them onwards and upwards.
17:08And?
17:09Upwards.
17:10Upwards.
17:11Upwards.
17:26Some get up and away first time.
17:28time.
17:39But many don't make it past the crashing surf.
17:58Some bedraggled chicks struggle back to shore.
18:15But for others, the pounding has been too much.
18:28Fewer than half of all the chicks on this colony survive their first three months of life.
18:56The coast of South Africa is an unforgiving place.
19:23The baby dolphins are still dependent on their mothers.
19:26They suckle for six months before they, like the young gannets, have to start fishing for themselves.
19:33There 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.
19:48But the sardine run might not even happen this year.
20:00For now, the dolphins will have to continue to scour the vast ocean.
20:09Back at the coast, other youngsters are getting ready to go it alone.
20:33Cape fur seals are also waiting for the sardines to come close to shore.
20:49But seals have a broad diet, so they can make the most of other feeding opportunities until the sardines come within range.
21:04Young seals are forced from the colony by the dominant males.
21:11Once they're cast out, the adolescents roam the coastline looking for food.
21:29They won't turn their noses up at a plump young gannet.
21:48Hungry seals patrol the surf, ready to pick off any birds that don't get airborne straight away.
22:03When the wind is light, the gannet chicks are stuck on the island.
22:10Surely they're safe here.
22:21But even on land, the seal is surprisingly fast on his flippers.
22:27All right.
22:48I don't know.
23:18In this one season, on this one colony alone, seals kill up to 10,000 fledglings.
23:37And as ever, it all comes down to sardines, for the seals are only after the fish within
23:44the stomach of their victims.
23:48For the young birds who do make it past the seals, there are fresh challenges, learning
23:55the skills of their parents.
23:59First, they have to find their quarry, the sardine shoals.
24:07And the best way to do that is to follow the expert trackers.
24:19They're hungry.
24:24It's been days since their parents last fed them.
24:30As the search goes on, the chicks are learning the most sophisticated survival technique
24:43of all.
24:44How to harness the expertise of another species.
24:56After a long search, the dolphins have found a small school of fish.
25:00They drive the sardines to the surface and within range of the young gannets.
25:09Now, quickly, they have to learn the art of the plunge dive.
25:13But there's a problem.
25:20The opportunistic seals have found the fish, too.
25:30The young gannets have a daunting choice, to risk diving with the enemy or to starve.
25:36If they don't take their chances soon, there will be nothing left.
25:55They're in luck.
25:56With sardines back on the menu, the seals ignore the gannets.
26:06As ever, the dolphins have done the hard work of rounding up the fish,
26:14and now a host of other predators take advantage.
26:21With the shoal diminishing by the second, competition is fierce.
26:26But there is still time for a mighty intruder.
26:36The brooder's whale devours the entire ball of fish.
26:48Until the sardine run starts in earnest,
26:51these minor skirmishes are mere preludes to the main event.
26:57But winter is finally on the way.
27:00The cold current pushes further north.
27:02This cool water forces its way up the coast.
27:07If it continues to flow northwards,
27:09it will carry great shoals of sardines with it.
27:17The predators begin to gather in anticipation of a feast.
27:21Sardines can't tolerate water above 20 degrees centigrade,
27:33so unless the cool water penetrates further up the coast,
27:36the fish won't move and the annual run just won't happen.
27:41Perhaps climate change has made its mark here.
27:44Perhaps climate change has made its mark here.
27:47The waters have stayed too warm, stalling the movement of fish.
27:51There hasn't been a sardine run for the past two years.
28:03The entire fleet is becalmed.
28:06N reload, terribly ahead of course,
28:09the cleaning water is troubled by the το rêve,
28:11Loch N
28:24A winter storm rolls in from the Antarctic, battering the Cape, bringing cold water.
28:54Driven by their hunger, gannets still try to hunt in these dangerous conditions.
29:11In fact, this wild weather is just what all the predators have been waiting for.
29:17For them, it's a perfect storm.
29:22It has pushed a narrow tongue of colder water up the coast.
29:27This chilly current carries wave after wave of sardines with it.
29:31Hemmed in by the land on one side and warm water on the other, the sardines are being
29:37drawn into a trap.
29:43Nature is playing a cruel trick on these unfortunate fish, as they'll get no benefit from their
29:48mass voyage.
29:52They're slaves to the cold ocean currents.
29:58More than 500 million fish are swimming towards disaster, and yet this is just a tenth of the
30:04sardine population.
30:06The run is on.
30:19Ahead an ambush is being prepared.
30:26As the seas begin to calm, the dolphins relocate the sardine shoals.
30:44As they track up the coast, the pods unite, combining forces.
30:57They form superpods of incredible numbers, up to 5,000 dolphins in one group.
31:11This is fast becoming one of the biggest groups of predators anywhere on the planet.
31:21The attackers spread out into wide hunting lines, stretching up to a mile across.
31:37Other divisions follow on, as ever, tracking the dolphins.
31:50Shadowing them all, the brooders wail.
32:02They're all heading in one direction, towards a place known as Waterfall Bluff.
32:15It's an arc in the coastline which interrupts the flow of currents, trapping the water in a swirling eddy.
32:25And the dolphins know that the massive shoals often get caught in this bottleneck.
32:41But these sardines have managed to avoid the trap.
32:48The first shoals have been carried well to the north of Waterfall Bluff, ahead of the dolphin superpods.
32:55As the cool water is squeezed into an ever-thinner band, closer to the shore, the shoals are forced up into the shallows.
33:09Only now do we get a real sense of the sheer wind.
33:24This one shoal stretches along the coast for 15 miles.
33:38The water is 15 meters deep and packed with sardines from top to bottom.
33:46There could be more than a hundred million fish in this single shoal alone.
33:52As 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.
34:00And the gannets can't risk diving into such shallow water either.
34:05But there are hunters who can follow.
34:12And they've arrived in their thousands.
34:16Sharks.
34:19Dusky copper and ragged tooth sharks encircle the sardines.
34:38Dusky copper and ragged tooth sharks encircle the sardines.
34:46But for the little fish, there's safety in such vast numbers.
34:51The sheer volume of sardines, the way they twist and turn in harmony, confuses the sharks.
35:04Without dolphins to round up the fish, these sharks have to find their own solution.
35:11They try to trap the fish against the water's surface.
35:31But this boiling water is mostly sardines escaping.
35:35Few are actually eaten.
35:37Tiny fish triumph over the marauding sharks.
35:51Tiny fish triumph over the marauding sharks.
35:53Tiny fish triumph over the marauding sharks.
36:05The sharks continue to harry the shoal, pushing it ever northwards.
36:09Back at Waterfall Bluff, the dolphins and gannets are waiting for the next pulse of sardines
36:26to come up from the south.
36:28If there's another shoal, this kink in the coastline is the perfect place to ambush them.
36:34But if the fish don't come, these hungry predators face their long journey all the way back to the Cape.
36:46To the north, the survivors of the shark attack are nearing the end of their run at the beaches around Durban.
36:58These seem like the lucky ones.
37:00On their epic journey, they've evaded an army of hunters.
37:06But one final unexpected predator lies in wait.
37:10Fishermen can only net the sardines once they've swum this far north within easy reach of the shore.
37:29Last year, no sardines were seen on this coast.
37:36So far this winter, the fishermen have landed only 50 tons, barely a tenth of what they'd expect in a good year.
37:51That's how unpredictable the sardine run has become.
37:55After such a long and hazardous voyage, it's a sad end for these sardines.
38:13At Waterfall Bluff, the dolphins and gannets have had to bide their time.
38:33After missing the first shoal, these predators are relying on the currents to sweep another big pulse of sardines up the coast.
38:41Now, another great shoal is on the way, and it's heading straight for Waterfall Bluff.
38:57Trapped between the shore on one side and the warm water on the other, these fish are swimming straight towards the enemy.
39:05The sardines fall back on their instinctive defense, swarming into a huge mass that confuses a predator.
39:25The sardines fall back on their instinctive defense, swarming into a huge mass that confuses a predator.
39:29But the dolphins have a strategy that turns this to their advantage.
39:45Working together, they separate off a pocket of sardines.
39:49In smaller numbers, the fish's shoaling defense now works against them.
40:00The dolphins corral the bait ball and herd it to the surface.
40:04This is what the other hunters have been waiting for.
40:24Now, the sardines are within range of the gannets.
40:27The bait balls form and re-form, seldom lasting longer than a few minutes each.
40:53The sharks pile in, taking advantage of the dolphins' hard work.
40:56The sharks pile in, taking advantage of the dolphin's hard work.
41:26The predators ignore each other.
41:32There's only one victim here.
41:34The millions of tasty little fish they've been stalking for so long.
41:56Young gannets join the frenzy.
42:02In just six months, they've become superb aerial hunters.
42:14Time after time, the dolphins round up another shoal for destruction.
42:20Frantically, the little fish tried to get away from the seething surface of the water.
42:46To dive beyond the range of the gannets.
42:52Now, something truly astonishing happens.
42:58Diving takes the gannets down to 10 meters.
43:02Then the aerial squadrons become shoals of swimmers as they pursue the fish down to 20 meters.
43:16Sardines join with the predators in a beautiful yet macabre underwater valley.
43:26There's little chance of escape for these fish.
43:30Mostly, on Monday of June, the turtles.
43:34With sharks and θ
43:41and submarines in the sand.
43:42I'm not��ering your beach with your Yunusmaker.
43:44Where to slide 6 inches.
43:46Hello, man.
43:47So, your photos and photos of démons.
43:49This is an slip and dialogue with drunken garden.
43:52The stage is set for the biggest predator of all.
44:22The brooder's whale takes in 10,000 fish in one giant mouthful.
44:31But this time around, there are plenty of sardines for all.
44:44Each hunter amongst these millions plays its part in the drama,
44:49and each is dependent upon the other.
45:06The annual spectacle of the sardine run
45:09is undoubtedly the greatest gathering of predators anywhere on the planet.
45:20It's surely one of nature's great events.
45:23THE END
45:24THE END
45:26THE END
45:28THE END
45:32THE END
45:36THE END
45:43THE END
45:45Let's go.
46:15Then, almost as quickly as it began, it's over.
46:23As the brief winter comes to an end,
46:25warm currents flowing south displace the corridor of cool water.
46:35Despite the massacre,
46:37more than half of all the sardines swept up on the Great Run survive.
46:46As the currents switch, the fortunate ones make good their escape.
46:54From here, they'll follow deep water currents,
46:57hitching a ride back to the cool waters of the Cape.
47:00The brooder's whale melts away to resume its secretive life
47:11somewhere out in the big blue.
47:14The dolphin's superpods break up and begin their long trek back to the Cape.
47:30Gannets, too, head south.
47:32As waterfall bluff falls quiet once more,
47:44no one can say whether this spectacular event
47:47will be repeated here in years to come.
47:50The sardine run may be unique to the coast of South Africa,
48:03but it's a vivid reminder of the riches
48:06that our oceans can still support.
48:09And we're back exploring Britain's secret seas here on BBC HD from half past six
48:26on Saturday.
48:40Next tonight, we're off to the Gulf.
48:42Of the Gulf.
48:44The Gulf.
48:59The Gulf of the Gulf
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