by some native cultures.

強大的神

For example, Fijians believe the shark god Dakuwaqa,

例如斐濟群島人相信鯊魚神 Dakuwaqa 能夠

could protect fisherman from the dangers at sea.

保護他們的漁民在海上安全無虞

And today, sharks are recognized as apex predators of the world's ocean

現今，鯊魚已被認為是海洋裡最頂端的掠食者

and include some of the Earth's longest living vertebrates.

也是地球上最長壽的脊椎動物 (部分種族)

What is it that makes these fish worthy of our ancient legends

是什麼讓這種魚類被我們的祖先一再稱頌

and so successful in the seas?

而且在海中又生活得這麼成功呢？

Much of their hunting prowess stems from a unique set of biological traits

鯊魚許多非凡的狩獵技術起源於

honed for more than 400 million years.

已演化超過四億年的特殊生物構造

Their cartilaginous skeletons are less dense than bony ones

牠們本身的軟骨結構密度比一般硬骨低，因此牠們

and require less energy to move.

移動所需能量比硬骨魚更少

Large oily livers lend buoyancy to their streamlined bodies,

巨大又富含油脂的肝臟提供牠們流線型的身體所需的浮力

and while trunk muscles of bony fishes attach directly to their skeletons,

硬骨魚的屈肌會連帶著骨頭一起動作

those of sharks also join to their skin.

而對鯊魚來說，這種連帶動作也會傳到牠們的皮膚上

This special design transforms them into pressurized tubes

這個特殊設計將肌力傳輸到加壓管裡

whose springy skin can efficiently transmit muscular forces to the tail.

加壓管有彈性的外皮能有效率地將肌力傳輸到尾部

Shark skin has additional remarkable features.

鯊魚的皮膚有另一個值得注意的特徵

Despite its smooth external appearance,

儘管從外面看起來它很平滑

at the micro level, it has a coarse texture

但在微觀尺度下，它卻是由成千上萬的

thanks to thousands of tiny teeth-like scales

微小齒狀鱗片組成的粗糙組織，它們

called dermal denticles.

稱為「皮齒」

Each denticle is coated in a substance called enameloid,

每個齒狀結構都被一種稱為 enameloid 的物質包覆著

which turns the skin into a tough shield.

它能將皮膚變得更堅硬

Plus the structure of denticles varies across the body

此外這些覆蓋全身的大量齒狀結構

in such a way as to reduce noise and drag

是為了在鯊魚游泳時減少

when the shark moves through water.

噪音和摩擦力

As for the teeth in their mouths,

至於說到鯊魚嘴裡的牙齒

sharks can produce up to 50,000 in a lifetime.

鯊魚一生中可以脫落五萬顆牙齒

On average, they can loose one tooth a week,

也就是說，鯊魚平均一周掉一顆牙齒

and each time that happens,

每次當鯊魚牙齒脫落時

it's rapidly replaced.

新牙很快的就會長出來填補空隙

Thanks to a layer of fluoride coating their teeth,

多虧了鯊魚牙齒上覆蓋的氟化物層

sharks also avoid cavities.

使得牠們不會蛀牙

But teeth aren't the same in all sharks.

但是並非所有鯊魚的牙齒都是相同的

They can vary across species and by diet.

不同種類和食性的鯊魚，牙齒也不一樣

Some are dense and flattened,

有些鯊魚牙齒密集而扁平

useful for crushing mollusks.

可以用來磨碎軟體動物

Others are needle-like for gripping fish.

有些則是擁有針狀牙齒，用來抓魚

The mouths of Great Whites contain pointy lower teeth for holding prey

大白鯊的嘴裡有非常尖的下齒用來固定獵物

and triangular serrated upper teeth for slicing.

而上齒則是三角鋸齒狀，用來將獵物切開

This variety enables sharks to target prey in a diversity of ocean environments.

這種多樣性讓鯊魚能夠在多樣化的海洋環境中獲取牠們的目標獵物

Many species also have another peculiar trait -

許多種族的鯊魚也有另一種特徵 —

the ability to launch their jaws out of their mouths,

讓上下顎的牙齒翻出嘴外的能力

open them extra wide,

把上下顎張得大大的

and grab prey by surprise.

並突然的咬住獵物

Over the course of evolution,

經歷了長期的演化

shark brains have expanded,

鯊魚的大腦功能以及

coupled with the growth of their sensory organs.

感知器官的功能也獲得了提升

Modern-day sharks can smell a few drops of blood

現代的鯊魚可以在800公尺遠處

and hear sounds underwater from 800 meters away.

就聞到幾滴血的味道，或是聽到水中的聲音

They're particularly well-tuned to low frequencies,

鯊魚對於低頻的聲音尤其有感應

including those emitted by dying fish.

包括垂死的魚放出的低頻，鯊魚也感應得到

And like cats, they have reflective membranes called tapeta lucida

就像貓咪一樣，鯊魚在眼球後方也有一層反射薄膜，

at the backs of their eyes

稱作「光神經纖維層」

that dramatically improve their vision in low light.

它能顯著地在昏暗的光線下增進鯊魚的視力

As if these heightened abilities weren't enough,

彷彿這些增加在鯊魚身上的能力還不夠

sharks have even honed a sixth sense.

鯊魚甚至磨練出了第六感

They're able to hunt using a network of electrosensory cells

他們能利用感電細胞網絡來打獵

called ampullae of Lorenzini.

這種感電器官稱為「羅倫氏壺腹」

These cells are filled with hypersensitive jelly

這些細胞填滿了能精密感應的膠狀物

which allows them to detect electrical signals from prey,

使得鯊魚們能偵測獵物的電場訊號

including the slightest twitch of a muscle.

連最輕微的肌肉顫動所放出的電都能感應到

Some of the most iconic shark species,

有些最典型的鯊魚種族

like Great Whites, Makos, Porbeagles, and Salmon Sharks

如大白鯊、尖吻鯖鯊、大西洋鯖鯊和太平洋鼠鯊等

owe their success to another surprising trait:

牠們的成功又歸於另一種令人驚訝的特質

warm blood inside a cold-blooded creature.

在牠們冷血生物的身體裡，竟然有溫暖的血液

Inside their bodies,

在鯊魚的身體裡

they have bundles of arteries and veins

有由多束動脈和靜脈組成的血管網絡

called rete mirabile.

稱為「細脈網」

Here, venous blood warmed up by the shark's working muscles

在這裡，鯊魚運動中的肌肉溫暖了靜脈裡的血

passes right next to arteries carrying cold, oxygen-rich blood from the gills.

並向右傳輸，靜脈的旁邊就是動脈，運送來自鰓部又富含氧氣的冷血

This arrangement transfers heat to the blood

這種排列方式將熱傳到血液裡

that gets cycled back to the body's vital organs.

並沿著循環回到鯊魚體內的重要器官中

Warmer muscles enable faster, more powerful swimming,

溫暖的肌肉讓牠們在游泳時更快更有力

while warmer bellies aid digestion,

溫暖的腹部可以幫助食物消化

and the more rapid development of young in utero.

也能讓子宮裡的寶寶發育得更快

And warmer eyes and brains keep the sharks alert in cold waters.

而溫暖的眼球和大腦則讓鯊魚在冰冷的水裡能保持警戒

With these amazing adaptations, there's more to revere than fear

有這麼多如此了不起的適應力，比起害怕，我們更應該崇敬那些

from the 500 shark species roaming our oceans.

在大洋裡漫游的500種鯊魚們

Unfortunately, one-third of these species are threatened

不幸地，由於過度捕撈，有三分之一的

due to overfishing.

鯊魚種族生存受到威脅

After millions of years in the making,

在幾百萬年來的演化後

these apex predators may be meeting their greatest challenge yet.

這些頂尖的掠食者或許正面臨牠們有史以來最大的危機