Meet the bluefin tuna, the toughest fish in the sea - Grantly Galland and Raiana McKinney

譯者: Man Chun Ma 審譯者: Amanda Zhu

What’s as big as a polar bear, swallows its prey whole,

什麼動物像北極熊這麼大， 把獵物完整吞噬，

and swims at 40 miles an hour?

又能以時速 40 英里游泳？

It’s not a shark or a killer whale.

牠不是鯊魚或殺人鯨，

It’s the Atlantic bluefin tuna.

牠是北方藍鰭鮪魚，

The largest and longest-lived of the 15 tuna species,

牠是 15 種鮪魚中最大、 最長壽的品種。

the Atlantic bluefin has a unique set of adaptations

北方藍鰭鮪魚演化出獨特的能力，

that make it one of the most dominant predators in the ocean.

令牠成爲海洋裡最強大的獵食者之一。

It starts as a tiny hatchling in the Gulf of Mexico or the Mediterranean Sea,

一開始牠們在墨西哥灣或地中海孵化，

no bigger than a human eyelash.

比人類的睫毛還小。

Within its first year of life,

在牠滿一歲前，

It develops something known as regional endothermy—

牠會發展出區域內溫性——

the ability to regulate its body temperature.

一種能調節身體溫度的能力。

An Atlantic bluefin gets oxygen from cold ocean water using its gills.

北方藍鰭鮪魚透過鰓 從冰冷的海水獲得氧氣，

This process cools its blood.

這個過程會令血液變冷，

Then, heat the tuna generates swimming and hunting warms the blood.

然後透過游泳和狩獵 產生的熱會令血液變暖。

In most fishes, this heat would be lost back out into the ocean through the gills.

就大部分魚類來說， 這些熱會透過鰓向海洋流失，

But in the Atlantic bluefin,

但北方藍鰭鮪魚

a mechanism called countercurrent exchange traps the heat.

則以一個叫做逆流交換 的機制來鎖住熱。

Cold blood on its way to the large swimming muscles

冰冷血液往大型游泳肌肉流動，

passes close to warm blood leaving those muscles

會近距離經過正要離開 那些肌肉的溫暖血液，

in a specialized network of blood vessels known as a rete mirabile.

這個血流交錯的區域構成 特有的血管網絡，稱為｢迷網｣。

Here the heat “jumps” to the cold blood and stays in the body.

熱會在這裡「轉移」到冷的血液中， 並留在體內而不流失。

This makes bluefin one of the few warm-blooded fishes,

這使藍鰭鮪魚成爲少數的溫血魚類，

a huge advantage in the marine environment.

在海洋環境中是個很大的優勢。

Cold-blooded animals whose body temperature

冷血動物的身體溫度完全取決於環境，

depends entirely on the environment become sluggish in colder waters.

使牠們在冰冷的水裡變得遲緩。

But a bluefin’s ability to keep warm means it has sharper vision,

而藍鰭鮪魚讓身體保持溫暖的能力 使牠的視野更銳利、

can better process information, and can swim faster than its prey.

處理資訊的能力更好、 比獵物游得更快。

It thrives in cold, deep, subarctic water.

牠在寒冷的亞北極水域深處茁壯成長。

Thanks to their warm bloodedness, their powerful muscles,

牠們仰賴溫血的身體、強健的肌肉，

and their streamlined torpedo shape

以及能將魚鰭收在體表溝槽內

with fins that fold into grooves to reduce drag,

以減少阻力的魚雷形流線身材，

bluefin tuna can reach speeds few other animals can match.

來達到少有其他動物 能與之比擬的速度。

Their maximum speed of 40 miles per hour

牠們的最高時速能達 40 英里，

is faster than that of a great white shark or orca whale,

比大白鯊和虎鯨的速度更快，

and even at their comfortable cruising speed,

就算以輕鬆的巡航速度，

they can cross the Atlantic in a couple months.

牠們也可以在幾個月內橫跨大西洋。

All this swimming requires a great deal of oxygen,

這樣游泳需要大量氧氣，

but the bluefin is adapted for this as well.

但藍鰭鮪魚也演化出適應的能力。

The faster it swims, the more water passes over its gills,

牠們游得越快，就有越多水流過鰓，

and the more oxygen it can absorb from that water.

也就能從水裡吸取越多的氧氣。

This need for a constant flow of water

為了有不間斷的水流，

means the tuna must always remain on the move.

牠們必須不停游動，

It also means bluefin cannot suck prey into their mouths

這也表示藍鰭鮪魚不能像 大多數其他魚類一樣，

the way most other fishes do.

將獵物吸入口中；

Instead, they must chase down their prey with their mouths open.

牠們必須張大嘴巴從後面追上獵物。

They eat smaller prey than most predators their size,

比起其他差不多身形的狩獵者， 牠們所吃的獵物更小，

including squid, crustaceans, and smaller fish species like mackerel.

包括魷魚、甲殼類 和較小型魚類，像是鯖魚。

The bluefin’s temperature-regulating ability

藍鰭鮪魚調控體溫的能力

doesn’t just make it a superior hunter— it gives it nearly unlimited range.

不僅讓牠成爲頂尖的狩獵者， 還令牠無遠弗屆。

As soon as they’re strong enough to swim against the current,

當牠們成長到能夠逆流前進時，

Atlantic bluefin leave the warm waters of their spawning grounds

北方藍鰭鮪魚會離開 牠們出生的溫暖水域，

and spend their lives hunting all over the Atlantic Ocean.

在大西洋各處狩獵。

Tunas from both the Gulf of Mexico and the Mediterranean Sea

從墨西哥灣和地中海來的鮪魚

frequent the same feeding grounds

會在相同的地點覓食——

and range from Brazil and Texas to Iceland and Senegal and beyond.

從巴西和德克薩斯州， 到冰島和塞內加爾，甚至更遠。

But when the time comes to reproduce around age 10,

但當牠們到了 10 歲的繁殖期時，

they always return to their sea of origin.

牠們總會回到自己出生的海域。

Here, groups of males and females release millions of eggs and sperm

在這裡，雄魚和雌魚會排出 成千上萬的卵子和精子到水裡。

into the water.

They’ll migrate back and forth between feeding and spawning grounds

牠們每年都會在覓食地 和繁殖地往返遷徙，

annually for the rest of their lives.

直到生命的盡頭。

Atlantic bluefin can live for over 40 years, growing all the while.

北方藍鰭鮪魚能活 超過 40 年，並不斷生長，

The largest specimens are tens of millions of times heavier than when they hatched.

體型最大者比剛出生時大上千萬倍。

The same huge size that makes bluefin tuna indomitable in the ocean

這個讓牠們稱霸海洋的龐大體積

has made them vulnerable to one predator in particular: us.

使牠們在一種獵食者前顯得特別脆弱， 這個獵食者就是我們人類。

Humans have a long history of fishing Atlantic bluefin—

人類捕獵北方藍鰭鮪魚的歷史久遠，

it’s even stamped on ancient Greek coins.

連古希臘的硬幣上也打有圖樣。

But in recent decades, demand has skyrocketed

而在近幾十年，藍鰭鮪魚的需求急增，

as bluefin are hunted for sashimi, sushi, and tuna steaks.

牠們被做成刺身、壽司和魚排。

An individual fish can sell for $10,000 or more,

單單一條魚就能賣得一萬美元以上，

promoting overfishing and illegal fishing.

使過漁和非法捕魚更爲猖獗。

But if recent conservation efforts are redoubled and quotas are better enforced,

但如果能夠加倍保育力度 和加強執行限額，

bluefin populations can begin to recover.

藍鰭鮪魚的數量可望回升。