Why are sharks so awesome? - Tierney Thys

譯者: Helen Chang 審譯者: SF Huang

Sharks have been celebrated as powerful gods

某些原住民文化 頌揚鯊魚是強大的神祇。

by some native cultures.

For example, Fijians believe the shark god Dakuwaqa,

例如，斐濟人相信鯊魚神

Dakuwaqa

could protect fisherman from the dangers at sea.

能保護漁民免於海上的危險。

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

如今鯊魚被視為海洋世界裡 頂尖的掠食性動物，

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

有些種類還是地球上 壽命最長的脊椎動物。

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

什麼因素使牠們 配得上古老傳說的稱頌，

and so successful in the seas?

並且在海洋裡獨霸一方呢？

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

大多數牠們高超的獵捕技能，

源自一套錘練超過四億年的 獨特生物特徵。

honed for more than 400 million years.

他們軟骨骨架的骨質密度 比硬骨魚類來得小，

Their cartilaginous skeletons are less dense than bony ones

and require less energy to move.

所以移動時所耗費的能量較少。

Large oily livers lend buoyancy to their streamlined bodies,

充滿油脂的大型肝臟 為流線型的身軀提供浮力；

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

不同於硬骨魚類的軀幹肌肉 直接附著在骨架上，

鯊魚的軀幹肌肉不僅連結骨架， 還連結著皮膚。

those of sharks also join to their skin.

This special design transforms them into pressurized tubes

這種特殊的設計使牠們形同加壓管，

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

具彈力的皮膚可以有效地 把肌力傳遞到尾巴。

Shark skin has additional remarkable features.

鯊魚皮膚有其它顯著的特點。

Despite its smooth external appearance,

儘管外觀光滑，

at the micro level, it has a coarse texture

但在顯微鏡下卻有著粗糙的質地，

thanks to thousands of tiny teeth-like scales

因為其體表覆蓋了數千片 齒狀的微小鱗片，

called dermal denticles.

我們稱為「盾鱗」。

Each denticle is coated in a substance called enameloid,

每個盾鱗都包裹著釉質，

which turns the skin into a tough shield.

使皮膚成為堅韌的保護層。

Plus the structure of denticles varies across the body

加上盾鱗的結構因應 身體各部位而有所不同，

in such a way as to reduce noise and drag

藉以減少鯊魚游泳時 所帶來的噪音與阻力。

when the shark moves through water.

As for the teeth in their mouths,

至於嘴裡的牙齒，

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

鯊魚一生中可以長出五萬顆之多。

On average, they can lose one tooth a week,

平均每週可掉一顆牙，

and each time that happens,

每次掉牙時，

it's rapidly replaced.

新牙迅速地遞補上。

Thanks to a layer of fluoride coating their teeth,

由於牙齒上覆蓋著一層氟化物，

sharks also avoid cavities.

鯊魚也免受蛀牙之苦。

But teeth aren't the same in all sharks.

但並非所有鯊魚的牙齒都相同，

They can vary across species and by diet.

會因物種和飲食而異。

Some are dense and flattened,

有些密而扁平，

useful for crushing mollusks.

利於壓碎軟體動物；

Others are needle-like for gripping fish.

另一些則為針狀，利於咬緊魚類。

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

大白鯊下排尖尖的牙齒托住獵物，

and triangular serrated upper teeth for slicing.

上排三角形鋸齒狀的牙齒 則用來切斷獵物。

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

這樣的多樣性使得鯊魚能在 不同的海洋環境中鎖定獵物。

Many species also have another peculiar trait -

許多鯊魚品種具備另一個特點－－

the ability to launch their jaws out of their mouths,

能把顎伸展、張開到嘴巴外面，

open them extra wide,

張到極大而能出其不意地捕獲獵物。

and grab prey by surprise.

Over the course of evolution,

在進化的過程中，

shark brains have expanded,

鯊魚的腦變大，

coupled with the growth of their sensory organs.

結合感覺器官的發展，

Modern-day sharks can smell a few drops of blood

現代的鯊魚 連幾小滴的血腥味都聞得到，

and hear sounds underwater from 800 meters away.

在水裡八百公尺之遙的聲音 也能聽到。

They're particularly well-tuned to low frequencies,

牠們對低頻的聲音特別敏銳，

including those emitted by dying fish.

包括垂死魚類發出的音頻。

And like cats, they have reflective membranes called tapeta lucida

和貓一樣，

牠們有著稱為 「光神經纖維層」的反光膜，

at the backs of their eyes

位於眼睛的後方，

that dramatically improve their vision in low light.

大大提高了低光照下的視力。

As if these heightened abilities weren't enough,

好像這些強化能力還不夠用似的，

sharks have even honed a sixth sense.

鯊魚甚至還具有敏銳的第六感，

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

能夠利用名為「羅倫氏壺腹」的 電覺細胞網絡來獵食。

called ampullae of Lorenzini.

These cells are filled with hypersensitive jelly

這些細胞充滿了極敏感的膠狀物，

which allows them to detect electrical signals from prey,

讓鯊魚能偵測到獵物 所發出的微弱電流訊號，

including the slightest twitch of a muscle.

包括輕微的肌肉抽動。

Some of the most iconic shark species,

一些最具指標性的鯊魚品種，

like Great Whites, Makos, Porbeagles, and Salmon Sharks

像大白鯊、尖吻鯖鯊、鼠鯊和鮭鯊，

owe their success to another surprising trait:

則擁有另一項異乎尋常的特質：

warm blood inside a cold-blooded creature.

牠們是冷血動物中的溫血動物。

Inside their bodies,

這些鯊魚的體內

they have bundles of arteries and veins

有間隔交錯的動脈和靜脈，

called rete mirabile.

稱為「細網膜」。

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

因鯊魚肌肉運動所產生的熱 而加溫的靜脈，

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

與從鰓輸送進來 冷而富含氧的動脈交相比鄰。

This arrangement transfers heat to the blood

這樣的排列能將熱度，

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

經由血液循環 送回到身體的重要器官。

Warmer muscles enable faster, more powerful swimming,

溫暖的肌肉使其游得更快、更有力，

while warmer bellies aid digestion,

溫暖的腹部能幫助消化，

and the more rapid development of young in utero.

亦能使子宮裡的小鯊魚長得更迅速。

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

溫暖的眼睛和腦， 使鯊魚在冷水裡保持警覺。

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

擁有這些驚人的適應能力，

我們應對漫游在海域的五百種鯊魚， 給予更多的崇敬而非畏懼。

from the 500 shark species roaming our oceans.

Unfortunately, one-third of these species are threatened

不幸的是，三分之一的鯊魚

受到過度捕撈而面臨生存的威脅。

due to overfishing.

After millions of years in the making,

在經過數百萬年的洗鍊後，

these apex predators may be meeting their greatest challenge yet.

這些頂尖的獵食者

可能正面臨著最大的挑戰。