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A storm petrel dancing on the water. But this is no amiable waltz. It's a hunt.
一只叉尾海燕在海面上跳舞。这不是可人的华尔兹。其实是在猎食。
As they hover facing into the wind, they pick out morsels from near the surface, including eggs.
当它们朝风翱翔时，会从水面附近撷取如鱼卵等碎食。
Only a tiny percentage of the developing eggs will survive long enough to hatch.
只有极小部分的卵能存活到孵化的时候。
These newly emerged tuna are only three millimetres long, and although they can swim, they're still very vulnerable.
这些新生的鲔鱼只有三公分长，虽然会游泳，但仍十分弱小。
It will be many weeks before they can swim strongly enough to make any real headway in the ocean.
它们需要好几个星期才真正够强壮，能够游向大海。
After the sun goes down, other predators rise from the depths to attack the floating multitudes.
日落后，其他的猎食者会从深海升起，攻击这些悬浮的鱼群。
Darkness shrouds the arrival of battalions of dangerous drifting predators.
黑夜为这一大群危险猎食者的到来提供掩护。
These shimmering comb jellies -- sea gooseberries -- trap their prey with sticky net-like webs.
这些闪亮的梳子水母，也就是海醋栗，用网子一般的黏网捕捉猎物。
One ill-timed fin-stroke could bring certain death to a hatchling fish.
如果拍打的时间不凑巧，可能就会使孵化中的幼鱼丧命。
There are many kinds of these comb jellies -- all of them very effective hunters.
梳子水母种类极多，都是猎食的好手。
By dawn, most of the nocturnal feeders will have returned to the depths.
大部分的夜行猎食者在日出前就会回到深海中。
The surviving hatchlings, however, have already started on their travels.
而存活下来的幼鱼，已经开始了它们的旅程。
Vast current systems, like immense rivers, carry them around the ocean basins.
巨大的洋流系统，像广大的河流，载着它们在海洋盆地活动。
The boundaries between these masses of moving water form invisible barriers that can trap both plankton and nutrients carried up from the depths.
这些巨大暗流的边缘形成隐形的界线，可以困住从深海升起的浮游生物及养分。
So parts of the ocean become rich with food for days or even weeks at a time.
所以海洋中某些海域会有几天，甚至几星期的时间食物充足。
This attracts vast schools of plankton-feeding fish -- like these sardine.
这些海域吸引了以浮游生物为生的鱼群前来，例如这群沙丁鱼。
They take in water through their mouths and expel it through their gills, sieving out the plankton which is then funnelled down their throats.
它们从口部吸取海水，再从鳃中排出，其中过滤出浮游生物，然后送到喉咙。
The immense schools travel along the boundaries of the currents, seeking the spots where the plankton is thickest.
庞大的鱼群跟着洋流的边缘行走，找寻浮游生物最浓密的区域。
As the position of the current boundaries changes constantly, so does both the supply of plankton and the numbers of fish.
洋流的边缘位置经常改变，所以浮游生物及鱼群的数量也在改变。
A small pod of Pacific Spotted Dolphin, twenty miles from the coast of Panama.
一小群热带斑海豚，在离巴拿马海岸20里的海域。
Like all predators, they seek parts of the ocean where their food is thickest.
就像其他肉食动物一般，找寻海中食物最丰盛的地带。
They cover as much as hundred miles in a day. And while they travel, they play.
它们一天可以游上100英里。一边行动，一边嬉戏。
They have detected the sound of schooling fish from hundreds of metres away and start to track down the shoals using sonar -- leaving their toys behind them.
它们察觉到在数百公尺外鱼群的存在，准备用声纳系统追踪鱼群，也离弃了它们的玩具。
For the hunted there are few places to hide.
而猎物也无处可躲。
Schooling mackerel. They have already sensed the sonar beams of approaching dolphin.
一群鲭鱼。已经察觉到逼近的海豚所发出的声纳。
Their only defence is to gather into a ball. Any individual that stayed out of the shoal would be quickly picked off.
它们唯一的抵抗方式就是聚集成一个球团。任何脱队的小鱼，马上就会被吃掉。
Within it, there is at least some chance of survival.
在群聚的球团中，还有些许生存的机会。
The noise of the attack alerts another predator -- a sailfish, one of the fastest fish in the ocean.
攻击的噪音惊动了另一只掠食者，旗鱼，海洋中游速最快的鱼类之一。
It has detected rapid vibrations in the water and is searching for the cause.
它察觉到了水中的快速震动，正在寻找原因。
Sailfish rely on eyesight for their final approach, so they hunt mainly in daylight.
旗鱼依赖眼力以作出最后一击，所以通常在白天行动。
When sailfish become excited they change colour, lighting up with bright blue stripes.
当旗鱼亢奋时，身体会变颜色，出现蓝色的条纹。
Since mackerel eyes are especially sensitive to blue and ultraviolet, these colours confuse them, making them easier to catch.
鲭鱼的眼睛对蓝色光及紫外线特别敏感，这些颜色使它们困惑，变得更容易手到擒来。
Far below, a blue shark returns from a squid-hunting trip in the cold darkness three hundred metres down.
在更深的下方，一只蓝鲨自一场位于300公尺深冷海水的乌贼猎食行动返回。
It's heading for the surface to reheat in the warmer water.
它正朝着水面前来，要让身体在暖水中回暖。
As it ascends, it detects the smell of oils and proteins shed into the water by the panicked mackerel.
当它开始上浮时，察觉到了鲭鱼群发出的蛋白质与脂肪的气味。
The trail leads both the shark and its attendant pilot fish towards an easy meal.
气味引领鲨鱼及它的领航鱼前来捡便宜。
Scraps and casualties float in the wake of the passing mackerel school.
碎片及鱼尸浮在鲭鱼群四周。
Throughout the ocean, predators and prey are locked in a deadly three-dimensional contest of hide and seek, played out over immense distances.
在海洋中，猎食者及猎物紧紧被锁在一个死亡的三度空间捉迷藏游戏中，游戏的范围十分广大。
To survive they must travel.
若要存活则必须迁徙。
The huge four metre long blue-fin tuna has special blood vessels that enable it to keep its body temperature significantly warmer than the surrounding water.
4公尺长的巨大蓝鳍鲔身上有特殊的血管，让它的体温可以保持在比周身海水较高的温度。
As a result, they can survive in much colder conditions than any other tuna,
所以它们可以在比较寒冷的条件下生存，
and they travel thousands of miles away from their spawning grounds in the tropics to hunt in cold seas where the food supply is richest.
它们会离开在热带的出生地，旅行到数千英里以外食物最丰饶的冷水域。
