that have ever roamed the planet.

最大的動物。

They're at least two times as big as the biggest dinosaurs,

藍鯨的體型比最大的恐龍 至少大兩倍，

"That's big!"

「真的很大!」

the length of a basketball court,

身長等同一座籃球場，

and as heavy as 40 African elephants.

且重量相當於四十隻非洲象。

If that's not enough to make you marvel,

如果這還不夠讓你驚訝，

here's something that will.

聽聽這個。

They're grown to this enormous size

藍鯨可以只靠食用一種

by feeding exclusively on tiny shrimp-like creatures called krill

我們稱為磷蝦的蝦狀小生物 就長得如此巨大。

that are no bigger than your little finger.

磷蝦的體型甚至不及你的小指頭呢。

In many ways, the sheer size of krill

從很多方面來看，磷蝦的大小

seems to have driven the evolution of the blue whale.

似乎促使了藍鯨演化成現在的樣貌。

See, krill are so small

磷蝦體型雖小

but are found in dense patches.

但大量成群出沒。

For increased efficiency,

為了提升效率，

blue whales have evolved

藍鯨演化出一種

to use a feeding strategy

特殊的覓食策略

called lunge feeding.

叫做「衝刺進食」。

Basically, the whale accelerates towards a prey patch

基本上，藍鯨覓食時會加速游向獵物

and opens its mouth wide.

並將嘴巴大大張開。

To increase the capacity, its mouth expands.

為了增加容量，它的嘴吧會不斷延展擴張。

The special, accordion-like blubber layer

從牠的鼻尖到肚臍

that extends from its snout to its belly button

有一層類似手風琴的特殊結構

enables the whale to engulf large quantities

使藍鯨可以大口吞入

of prey-laden water.

富含獵物的海水。

With each giant gulp,

這每一大口，

the whale takes in 125% of its body weight

藍鯨都吞入相當於牠體重 1.25 倍的

in water and krill.

海水和磷蝦。

The whale must then expel the water

接著牠必須排出吞入的海水，

while retaining the yummy krill.

並留住美味的磷蝦大餐。

To do this, it uses its baleen,

此時，鯨鬚便派上用場，

the comb-like structure made of the same stuff

鯨鬚是一種梳子狀的構造，

our nails and hair are made of,

成分和我們的指甲及頭髮一樣，

and its tongue.

牠的舌頭也同樣有所貢獻。

It's pretty crazy that the blue whale's heart

藍鯨的心臟跟一台小型車一樣大

is as big as a small car,

聽起來實在難以置信，

a child could crawl through its arteries,

牠的動脈大得足以讓小孩在裡頭爬行，

its tongue weighs as much as an elephant,

光是牠的舌頭，就跟一隻大象一樣重，

but its esophagus is so small,

不過牠的食管，

the whale could choke on a loaf of bread.

卻小到難以吞嚥一條麵包。

These whales are really not designed

看起來，藍鯨還真的不適合

to feed on anything larger than krill.

吃比磷蝦還大的食物。

It's estimated that blue whales eat four tons of krill per day.

根據估計，藍鯨一天可以吃下四噸的磷蝦。

Because of the incredible design,

因為這種奧妙的構造，

each dive provides the blue whale

藍鯨每一次進食

with 90 times as much energy as is used.

所獲取的能量 為其所消耗的九十倍。

Every mouthful of krill provides almost 480,000 calories,

每一口磷蝦，藍鯨都能從中攝取 四十八萬卡路里，

the same amount you get from eating 1,900 hamburgers.

相當於 1900 個漢堡的熱量。

But, why are blue whales so big?

不過，藍鯨究竟為何這麼巨大?

Blue whales are considerably larger

甚至連陸地上最大的動物──大象，

than the largest living land animal, the elephant.

跟牠比起來都是小巫見大巫。

The heavier an animal is,

動物的重量

the greater its relative surface area.

和其相對表面面積成正比。

As weight increases,

當體重增加到了某個限度，

there's a point at which the legs of that animal

動物就會因為腳承受不住重量

would simply collapse.

而摔倒在地。

That explains why elephants don't stand

這解釋了為什麼大象的四肢

on the delicate legs of a horse.

不像馬那樣纖細精緻。

They need legs shaped like stout pedestals

大象的腳必須像結實的圓柱，

to hold their bodies up against gravity.

來支撐身體的重量。

In water, the situation is quite different.

在水中，情況則大相逕庭。

Buoyancy counteracts the gravitational pull on the body

浮力會抵消地心引力，

and their great bulk is therefore partially supported

因此藍鯨龐大的身軀

by the water.

有一部份是被水的浮力支撐住的。

So, the ocean is a great place for species

海洋可以說是提供了 想要長得大一點的動物

that want to grow bigger.

一個絕佳的環境。

The other secret to their size is their diet.

飲食也在 龐大的身軀背後扮演重要的角色。

By evolving such a huge mouth,

經演化而成的巨大嘴巴，

the whale's have specialized to catch enormous quantities

使藍鯨能夠輕易地捕獲

of highly abundant and nutritious prey,

大量營養豐富的獵物，

which provides the energy needed to grow so big.

提供其長到如此巨大所需的能量。

But, now maybe you're wondering

不過，你可能納悶

why blue whales aren't any bigger?

為何藍鯨沒有繼續無限制長大?

After all, the ocean sounds like nirvana

畢竟，乍聽之下，

for any growing beast.

海洋像是 這些龐然大物的樂土。

Well, while lunge feeding may have allowed blue whales

這麼說好了， 雖然「衝刺進食」

to become the biggest animal

使藍鯨成為

to have ever roamed the planet,

地球上有史以來最大的動物，

by enabling them to feed efficiently in dense prey patches,

但這樣高效率的進食模式

it isn't cost free.

並非沒有代價。

Scientists compared all the costs involved with lunge feeding

科學家將「衝刺進食」所需代價

to the energy gained from the krill they eat.

與從磷蝦身上獲取的能量 做了比較。

What they found is that when the whale's body increases in size,

發現藍鯨隨著體型增長

the energy that body demands rises faster

身體所需能量的成長速度

than the extra energy they get from their food.

遠超過食物來源所能提供的量。

Feeding whales needs 15 times the energy required to remain still

「衝刺進食」所需能量 是維持靜止時的十五倍，

and 5 times more energy than used when swimming.

也是游泳時的五倍。

Calculations show

根據計算，使用「衝刺進食」的動物

that the largest a lunge feeder can grow is 33 meters,

最多可以長到三十三公尺長，

pretty much blue whale size.

約略是藍鯨的大小。

Turns out blue whales have a lot to thank krill for:

看起來藍鯨可是欠了磷蝦不少人情：

neat, evolutionary adaptations

若非磷蝦這麼小，

that would not have been possible if krill were not so small.

藍鯨不可能發展出 這麼細緻的、演化上的環境適應。

It's incredible that these tiny creatures

像磷蝦這麼小的生物

have allowed blue whales to really push the limits

竟能使藍鯨挑戰 地球上生物體形的最大極限，

of size on our planet.

確實令人嘖嘖稱奇。

Makes you wonder if that old adage,

不禁使人懷疑，

"You are what you eat,"

「人如其食」這句俗語

really does apply in blue whale world.

似乎不適用在藍鯨身上。