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Nutrients also well up to the surface along the coasts of the continents.
海底上来的养分可以抵达各大洲的海岸。
This is Natal on South Africa's eastern seaboard.
这里是位于南非东岸的纳塔尔。
It's June and just off-shore, strange black patches have appeared.
现在是六月，而就在海边不远处，奇怪的黑斑块出现了。
They look like immense oil slicks up to a mile long. But this is a living slick.
看起来像一大片油污绵延数里。这其实是一条有生命的滑带。
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.
千百万的沙丁鱼，其生物量足以与非洲草原上的羚羊匹敌。
These fish live for most of the time in the cold waters south of the Cape, but each year the coastal currents reverse.
这些鱼群大部分的时间都生活在好望角以南的冷水中，但是沿岸流每年都会转向。
The warm Agulhas current that usually flows down from the north has been displaced by cold water coming up from the south, and that has brought up rich nutrients.
通常由北而下温暖的安哥拉海流，被从南而上、带有丰富营养的冷海水所取代。
They, in turn, have created a bloom of plankton, and the sardines are now feasting on it.
这些冷海水造就了丰富的浮游生物，这些沙丁鱼则正在享用大餐。
As the sardines travel north, a whole caravan of predators follow them.
沙丁鱼向北游的同时，一大群掠食者紧随在后。
Thousands of Cape Gannets track the sardines.
几千只好望角塘鹅紧盯着这些沙丁鱼。
They nested off the Cape, and timed their breeding, so that their newly-fledged chicks can join them in pursuing the shoals.
它们在好望角筑巢，算好时间生育，这样它们羽翼初丰的幼鸟可以随它们一起追逐鱼群。
Below water, hundreds of sharks have also joined the caravan.
在海底，数百只鲨鱼也加入了。
These are Bronze whaler sharks, a cold water species that normally lives much further south.
短尾白眼鲛是一种生活在冷水中的鲨鱼，通常栖息在更远的南边。
These three-metre sharks cut such great swathes through the sardine shoals that their tracks are clearly visible from the air.
这些身长3公尺的鲨鱼可以在丰厚的沙丁鱼中切出一道从空中也清楚可见的通道。
Harried by packs of predators and swept in by the action of the waves, the sardine shoals are penned close to the shore.
被这些掠食者及海浪冲击的沙丁鱼群，渐渐被导近了海岸。
Common dolphin are coming in from the open ocean to join the feast. There are over a thousand of them in this one school.
真海豚也从海上来到加入盛宴。这一群就有一千只以上。
When they catch up with the sardines, the action really begins. Working together, they drive the shoal towards the surface.
当它们赶上沙丁鱼时，行动才真正开始。它们会全体合作，将鱼群赶到靠近水面的地方。
It is easier for the dolphins to snatch fish up here. Now the sardines have no escape.
海豚在靠水面的地方比较容易捕捉到鱼。这些沙丁鱼无处可逃了。
Thanks to the dolphins, the sardines have come within the diving range of the gannets.
因为海豚的帮忙，这些沙丁鱼游到了塘鹅潜水的深度范围。
Hundreds of white arrows shoot into the sea, leaving long trails of bubbles behind each dive.
好几百只白色羽箭射入水里，在身后留下一道道长长的泡沫。
Next to join the frenzy are the sharks. Sharks get very excited when dolphins are around.
接着加入这场混战的是鲨鱼。有海豚在附近，鲨鱼就会变得兴奋异常。
That may be because they can feed particularly... well once the dolphins have driven the sardines into more compact groups near the surface.
也许是海豚会将这些沙丁鱼赶到水面附近，形成更紧密的鱼群，让鲨鱼们吃的更好更顺利。
As the frenzy continues walls of bubbles drift upwards. They are being released by the dolphins, working together in teams.
混战当中，一道道泡沫墙向上浮起。这是结队合作的海豚所释放的。
They use the bubbles to corral the sardines into ever tighter groups.
它们利用这些泡沫将沙丁鱼赶成更紧密的鱼群。
The sardines seldom cross the wall of bubbles and crowd closer together.
沙丁鱼很少会跨过泡沫墙，所以只好更紧密地靠在一起。
Bubble netting in this way enables the dolphins to grab every last trapped sardine.
这样的泡沫网，让海豚可以吃到每一只受困的沙丁鱼。
Just when the feasting seems to be almost over, a Bryde whale arrives.
就在大餐快要结束之时，一只布氏鲸抵达。
The survivors head on northwards, and the caravan of predators follows them.
幸存者继续往北方前进，这群掠食者则跟随在后。
