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  • Sharks have been celebrated as powerful gods

    鯊魚經常被一些本土文化描寫為

  • 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

Sharks have been celebrated as powerful gods

鯊魚經常被一些本土文化描寫為

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B2 中高級 中文 TED-Ed 鯊魚 牙齒 獵物 溫暖 靜脈

【TED-Ed】為什麼鯊魚這麼棒? (Why are sharks so awesome? - Tierney Thys)

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    沙渺 發佈於 2017 年 03 月 01 日
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