Eli the eel: A mysterious migration - James Prosek

鰻魚伊萊：神秘的遷移－James Prosek

Transcriber: Jessica Ruby Reviewer: Caroline Cristal

譯者: Yamei Huang 審譯者: Qiwen Lu

They're long and slithery,

牠們很修長，全身滑溜溜，

and they're not very colorful.

而且沒有鮮艷的色彩。

But they do have a strange beauty of their own.

但是牠們俱有一種獨特的美感。

Their sinuous, nocturnal movements

夜裡，牠們在水中

through the water

are mesmerizing to watch.

彎曲地移動，

令人歎為觀止。

And though they may resemble underwater snakes,

雖然牠們很像水蛇，

eels are, in fact, a very interesting type of fish.

實際上，牠們是鰻魚，一種很特別的魚類。

There are several things about eels

除了修長的身形，沒有四肢外，

that make them unique

鰻魚有許多特徵

besides their elongated shape and limbless bodies.

讓牠們看起來獨一無二。

For one thing,

首先，

eels have the ability to breathe through their skin.

鰻魚可以透過皮膚呼吸。

Some can even leave the water

有的甚至可以離開水面

and move over land for short periods.

在陸地上存活一小段時間。

And, unlike most migratory fish,

不像大部分有遷移習性的魚類，

such as salmon,

如鮭魚，

which spawn in fresh water

在淡水中產卵

but live their adult lives in salt water,

卻在海水中成長，

eels of the genus Anguilla

安圭拉島的鰻魚

migrate in the opposite direction,

以相反的方向遷移，

spawning and breeding in oceans and seas,

牠們在海洋中產卵和繁殖，

while spending most of their intervening time

大部分的時間

in fresh water.

在淡水中成長。

If we were to take one such fresh water eel

如果我們跟隨一條淡水鰻魚

and follow its life story,

來了解牠的生活故事，

it would be born in the middle of the North Atlantic Ocean,

那就是牠出生於北太西洋中，

about a thousand miles east of Bermuda.

游到百慕達的東部約 1000 英哩的地方，

This area, called the Sargasso Sea,

這個區域，稱為馬尾藻海，

forms the western part

也就是亞熱帶環流

of a subtropical gyre,

的西半部，

a giant whirlpool in the middle of the ocean.

在海洋中有一個巨大的漩渦。

Our eel, let's call it Eli,

讓我們稱這條鰻魚為伊萊，

would begin as one of ten to twenty million tiny eggs,

當雌鰻魚帶著這個千萬分之一的小卵時，

carried by a female eel,

牠的生命由此開始，

hatching into a transparent leaf-shaped thing

然後孵化成透明且葉子形狀的東西

that looks nothing like an adult eel.

這看起來一點也不像鰻魚。

Eli starts to drift in ocean currents,

伊萊隨著海潮漂流，

predominantly the Gulf Stream

順著墨西哥灣流的方向

towards either Europe or North America,

依種類的不同

depending on its particular species.

游向歐洲或北美洲。

Upon reaching the coast,

當到達岸邊時，

Eli is about two inches long,

伊萊大約有兩英吋長了，

looking more eely but still transparent,

這時形狀看起來比較像鰻魚， 但仍然是透明的身體，

known at this stage as a glass eel.

這個時期，大家稱牠為玻璃鰻。

But within a couple of days in fresh water,

但生活在淡水的幾天後，

Eli's skin becomes pigmented a brownish-black,

伊萊的皮膚變成無光澤的黑褐色，

now looking more like that of an adult eel.

這時看起來比較像鰻魚。

You might notice

你也許注意到一件事

that we haven't mentioned anything

我們還沒提到

about Eli's gender yet.

伊萊的性別。

That's because this is only determined

這是因為性別是在鰻魚

once an eel enters fresh water,

進入淡水時的情況而定，

though nobody is sure exactly how that happens.

沒有人能確切知道真實的狀況。

Most of the eels that stay in the estuaries

大部分的鰻魚會停留在出海口，

and brackish water become males,

帶有微鹹的水域讓鰻魚變成雄性，

while those that go upstream become females,

那些往河流上游游去的鰻魚變成雌性，

growing up to two to three times bigger than

雌鰻魚會長到比未來的配偶

their future mates.

還要大上兩至三倍。

In this case,

在這個情況下，

it turns out that Eli was actually short for Elaine.

伊萊變成是‎伊萊恩。

As a female eel,

一條雌鰻魚，

Elaine will be quite solitary

‎伊萊恩在大部分時間

for most of her life in the stream,

獨來獨往地生活於淡水河中，

eating whatever falls in the water:

牠吃任何掉入水中的東西：

grasshoppers, crickets, small fish,

蚱蜢，蟋蟀，小魚，

insect larvae, frogs, baby birds,

幼蟲，青蛙，雛鳥，

almost anything she can get her mouth around.

任何她嘴巴能輕易取得的東西。

And she will grow quite big,

她可以長得相當大，

up to four feet long

直到四呎長

and weighing as much as thirteen pounds.

重量達十三磅。

We don't know exactly how

我們無法確切得知

fresh water eels know when it's time

在淡水中生活的鰻魚，

to return to the ocean,

怎會知道何時要回到海洋，

but something calls to them.

一定有某種力量在召喚牠們。

And their fall migration

牠們的秋季遷移

is one of the largest unseen migrations

是地球上

on the planet.

前所未見的大遷移之一。

As Elaine leaves fresh water for the ocean,

當‎伊萊恩離開淡水游往海洋，

she undergoes a shocking metamorphosis.

她經歷一個令人驚訝的蛻變。

Her eyes enlarge by about ten times,

她的眼睛變大十倍，

her skin gets thicker,

皮膚變得比較厚，

and her fins get larger.

鰭也變得更大。

These are most likely adaptations

這是為了適應牠將在海洋中的旅程

for their upcoming ocean travel,

所做的變化，

and Elaine seamlessly makes the transition

從淡水到鹹水的過程中

from fresh to salt water,

‎伊萊恩悄悄地做了轉變，

which would be toxic for most other fish.

但鹹水對大部分的魚類來說是有害的。

Once Elaine leaves the mouth of the fresh water streams,

‎一旦伊萊恩離開淡水河口，

she will disappear completely from human view.

她就完全消失在人類的視線中。

No one has witnessed,

沒有人目睹，

or been able to follow,

或跟蹤

an adult eel on their migration,

一條成人鰻魚的遷移，

nor do we know how deep they spawn.

我們不知牠們在多深的海域產卵。

But it's assumed that they can follow some signs

假設牠們能夠偵測訊號，

that they can detect,

然後隨著這些訊號游回海洋，

such as a thermal barrier between ocean currents

如：洋流之間的熱障

or a salinity front,

或是鹽度，

in order to return to the same area of the ocean

這是為了回到

where they were born.

牠們出生的海洋。

Because we don't even know exactly

我們不是很了解

what happens during an eel's migration,

在鰻魚遷移當中，發生了什麼事，

we can only imagine what the actual breeding looks like.

我們只能想像牠繁殖的情況。

But the common hypothesis

一般的假設是：

is that Elaine and thousands,

‎伊萊恩和數千個的，

or hundreds of thousands,

或成千上萬的

of other eels

其他鰻魚

gather in large, intertwined masses

聚集成一大群，互相糾纏在一起

and release their eggs and sperm

儘情地進行隨機交配，

in a giant orgy known as panmixia.

然後產出卵子和精子。

A couple of days after the eggs are laid,

卵被生下的幾天後，

they hatch,

牠們孵化了，

and the cycle begins again.

然後又再次循環這個過程。

And because we've never seen

因為我們從沒目睹過

the adult eels returning up the fresh water rivers,

成年鰻魚游回淡水河的情形，

we must assume that,

我們必需如此假設：

having completed their long and roundabout journey,

這些神奇且神秘的生物，

these amazing and mysterious creatures

在完成長途且曲折的旅程後，

finally die there,

最後消逝

in the same place where they were born.

在牠們出生的海洋中。

Goodbye, Elaine!

再見，伊萊恩！

It was a pleasure knowing you.

很高興認識你。