Why are sharks so awesome? - Tierney Thys

翻译人员: Ping Hu 校对人员: Amy H. Fann

Sharks have been celebrated as powerful gods

在一些土著文化中

by some native cultures.

鲨鱼被当作强大的神而崇拜

For example, Fijians believe the shark god Dakuwaqa,

例如斐济文化中所崇拜的鲨鱼神

could protect fisherman from the dangers at sea.

可以保护渔民免除海上的危险

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

现在，鲨鱼是世界海洋中的顶尖掠食者

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

包括一些在地球上存活了很久的脊椎动物在内

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

是什么使得鲨鱼这一古老的传奇

and so successful in the seas?

在今天的海洋中还能如此成功

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

鲨鱼的很多捕食技能都来源于一整套独特的生理特质

honed for more than 400 million years.

这些生理特质从4亿多年中进化而来

Their cartilaginous skeletons are less dense than bony ones

它们软骨质的骨架比硬骨的骨架更轻

and require less energy to move.

在游动时更加节省能量

Large oily livers lend buoyancy to their streamlined bodies,

它们巨大的油质肝脏为流线型的身体提供浮力

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

与其它硬骨质的鱼类不同

those of sharks also join to their skin.

鲨鱼的躯干肌肉不仅直接附着在骨架上也连接着他们的皮肤

This special design transforms them into pressurized tubes

这一特殊的生理机能增加了鲨鱼身体内部的弹性

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

它们像弹簧一样的皮肤将肌肉的力量有效的传递到尾部

Shark skin has additional remarkable features.

鲨鱼的皮肤还有别的独到之处

Despite its smooth external appearance,

虽然从外面看上去十分光滑

at the micro level, it has a coarse texture

但是在显微镜下有着粗糙的纹路

thanks to thousands of tiny teeth-like scales

鲨鱼皮肤表面布满了成千上万微小的齿状麟片

called dermal denticles.

称之为盾麟

Each denticle is coated in a substance called enameloid,

每一片盾麟都覆盖着一层釉质

which turns the skin into a tough shield.

这使表面异常坚固

Plus the structure of denticles varies across the body

而且这些盾麟的结构因身体部位不同而各异

in such a way as to reduce noise and drag

以减少鲨鱼在水中游动时

when the shark moves through water.

带来的噪音和阻力

As for the teeth in their mouths,

至于鲨鱼的牙齿

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

它们一生可以长出五万个牙齿

On average, they can lose one tooth a week,

鲨鱼可以平均一个星期掉一颗牙

and each time that happens,

而且每次掉一颗牙

it's rapidly replaced.

很快就会有新的牙齿长出来

Thanks to a layer of fluoride coating their teeth,

鲨鱼牙齿表面的氟化物涂层

sharks also avoid cavities.

还可以使它们免除蛀牙的苦恼

But teeth aren't the same in all sharks.

不同的鲨鱼牙齿通常也不同

They can vary across species and by diet.

取决于它们的种类和食物

Some are dense and flattened,

有些是紧密而平整的

useful for crushing mollusks.

用来磨碎软体类的动物

Others are needle-like for gripping fish.

还有些是针头一样尖的用来抓鱼

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

大白鲨的下牙低而突出用来捉住猎物

and triangular serrated upper teeth for slicing.

它们三角锯齿状的上牙则用来切削

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

这种多样性使得鲨鱼可以在广阔的海洋环境中选择目标猎物

Many species also have another peculiar trait -

很多种类的鲨鱼还有一个独特的本领

the ability to launch their jaws out of their mouths,

它们可以把下颌从嘴里伸出来

open them extra wide,

把嘴张得巨大

and grab prey by surprise.

突击捕食猎物

Over the course of evolution,

在不断的进化进程中

shark brains have expanded,

鲨鱼的大脑扩张了

coupled with the growth of their sensory organs.

与此同时它们的传感系统器官也更发达

Modern-day sharks can smell a few drops of blood

现代鲨鱼连几滴血液的味道都能嗅到

and hear sounds underwater from 800 meters away.

听觉达到了水下800米以远

They're particularly well-tuned to low frequencies,

尤其能够识别低频声波

including those emitted by dying fish.

包括哪些濒死的鱼类发出的声波

And like cats, they have reflective membranes called tapeta lucida

在鲨鱼的后眼角位置有一种反光膜

类似于猫眼的反光组织

at the backs of their eyes

that dramatically improve their vision in low light.

极大提高了黑暗中的视力

As if these heightened abilities weren't enough,

似乎这些高大上的特质都还不够

sharks have even honed a sixth sense.

鲨鱼还进化出了第六感

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

它们能够利用细胞网状系统的电波来捕猎

called ampullae of Lorenzini.

这个系统被称为鲨鱼的电感受器

These cells are filled with hypersensitive jelly

这些细胞充盈着高度敏感的胶状物

which allows them to detect electrical signals from prey,

而胶状物使得鲨鱼能够探测到猎物发出的电流信号

including the slightest twitch of a muscle.

即便是极其微小的肌肉颤动

Some of the most iconic shark species,

一些最具代表性的鲨鱼种类

like Great Whites, Makos, Porbeagles, and Salmon Sharks

比如大白鲨、灰鲭鲨、鼠鲨以及鲑鲨

owe their success to another surprising trait:

还拥有另一种令人惊讶的特点

warm blood inside a cold-blooded creature.

在他们冷血动物的头衔下有着恒温的内在

Inside their bodies,

鲨鱼体内

they have bundles of arteries and veins

有着相互交织的动脉和静脉

called rete mirabile.

称之为细脉网

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

在这里，被工作肌群变暖的静脉血

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

与从鳃部获得的富氧的冷动脉血擦肩而过

This arrangement transfers heat to the blood

这样就把热量通过血液传递给了

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

身体各部分的重要器官

Warmer muscles enable faster, more powerful swimming,

温暖的肌肉使鲨鱼游的更快更有力

while warmer bellies aid digestion,

温暖的腹部有助于消化

and the more rapid development of young in utero.

同时鲨鱼宝宝们在子宫里也成长的更快

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

温暖的眼睛和大脑使得鲨鱼在寒冷的水中保持警觉

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

鲨鱼这些奇妙的适应性带来的更多的应该是崇敬而不是畏惧。

from the 500 shark species roaming our oceans.

很不幸的是，在全球海洋500种的鲨鱼中

Unfortunately, one-third of these species are threatened

有高达三分之一的种类

due to overfishing.

受到过度捕捞的威胁正在消亡

After millions of years in the making,

经历了上百万年的洗礼之后

these apex predators may be meeting their greatest challenge yet.

鲨鱼这一世界海洋中的顶尖掠食者也许正在遭遇着最大的挑战