How giant sea creatures eat tiny sea creatures - Kelly Benoit-Bird

大魚如何吃小蝦 - Kelly Benoit-Bird

Transcriber: Andrea McDonough Reviewer: Jessica Ruby

譯者: Hao-Wei Chang 審譯者: Geoff Chen

One of the reasons that I'm fascinated by the ocean

我對海洋著迷的其中一個原因是

is that it's really an alien world on our own planet.

它是地球上陌生的區域

From our perspective,

從我們的觀點

sitting on the shoreline or even out on a boat,

坐在海灘、甚至是船上

we're given only the tiniest glimpses

我們對浪花之下

at the real action that's happening

所發生的事情

beneath the surface of the waves.

所知甚少

And even if you were able to go down there,

即使你潛入水下

you wouldn't see very much

你也看不到多少

because light doesn't travel very far in the ocean.

因為光線在海水中穿透力很差

So, to answer questions about how the ocean works,

所以為了回答我想問的問題

in my research, we use sound.

在我們的研究中是用聲音

We use sonars that send out pulses of sound

我們用聲納送出

made up of a number of different frequencies, or pitches,

由不同頻率和強度組成的音波

that are shown with different colors.

這在圖上以不同顏色標示

That sound bounces off things in the habitat

聲波撞到棲地中不同東西時

and comes back to us.

就會回傳給我們

If it were to bounce off this dolphin,

如果聲波被海豚阻擋

the signal we got back

我們收到的訊號

would look very much like the one we sent out

和發出去的相去不遠

where all the colors are represented pretty evenly.

在圖上就是不同顏色平均分佈

However, if we were to bounce

但是如果是撞到

that same sound off of a squid,

讓我們假設

which in this case is about the same size as that dolphin,

一隻和海豚一樣大的烏賊

we'd instead only get the lowest frequencies back strongly,

我們只能得到低頻率的回波

shown here in the red.

在圖上以紅色標示

And if we were to look at the prey of that squid,

讓我們看看烏賊的獵物

the tiny little krill that they're eating,

那些牠們所吃的小磷蝦（krill）

we would instead only get the highest frequencies back.

我們只能得到高頻率的回波

And so by looking at this,

所以藉此

we can tell what kinds of animals are in the ocean,

我們可以知道海中有哪些生物

we can look at how dense they are,

牠們的密度如何

where they are distributed,

以及牠們的分佈

look at their interactions

互動

and even their behavior

甚至行為

to start to study the ecology of the ocean.

藉此研究海洋生態學

When we do that, we come up with

當我在進行研究時

something sort of surprising:

我們遇到了許多驚奇

on average, there isn't very much food in the ocean.

平均而言，海中的食物不多

So even in places which we think of as rich, the coasts,

即使在被認為 食物豐富的珊瑚礁區

we're talking about two parts of every million contain food.

也只在每 5 萬分之 1 的地方有食物

So what does that mean?

這代表什麼呢？

Well, that means that in the volume of this theater,

以今天講堂大小的空間而言

there would be one tub of movie theater popcorn

只有一桶爆米花

available to be eaten.

可供大家享用

But of course, it wouldn't be collected

但這些爆米花不回集中在一起

for you neatly in this bucket.

讓你舒服的想用

Instead, you'd actually have to be swimming

事實上，你必須在其中

through this entire volume Willy Wonka style,

以威利．旺卡的方式游泳（Willy Wonka）

picking off individual kernels of popcorn,

才能吃到四散各處的爆米花

or perhaps if you were lucky,

也有可能你很幸運

getting a hold of a few small clumps.

拿到了一小塊

But, of course, if you were in the ocean,

當然如果在海洋

this popcorn wouldn't be sitting here

這些食物不會等在那裡

waiting for you to eat it.

讓你來吃

It would, instead, be trying to avoid becoming your dinner.

它們會盡力避免被捕

So I want to know how do animals solve this challenge?

我想知道動物如何克服這項挑戰

We're going to talk about animals in the Bering Sea.

我會談談在白令海中的生物（Bering Sea）

This is where you may have see "Deadliest Catch" framed,

你們可能會在致命捕撈中（Deadliest Catch）

in the northernmost part of the Pacific Ocean.

看到的太平洋最北端水域

We've been looking specifically at krill,

我們專注在磷蝦觀察上

one of the most important food items in this habitat.

牠們是這棲地中 最重要的食物來源之一

These half-inch long shrimp-like critters

這些半英尺長、長得像蝦子的動物

are about the caloric equivalent

所能提供的熱量

of a heavily buttered kernel of popcorn.

大概和一顆重奶油爆米花相同

And they're eaten by everything

而牠們是大家的食物

from birds and fur seals that pick them up one at a time

從海鳥、海狗一口一隻的吃

to large whales that engulf them in huge mouthfuls.

到大鯨魚一次吞下一大群

So I'm going to focus in the area

所以我們專注在

around three breeding colonies for birds and fur seals

白令海的東南部

in the southeastern Bering Sea.

是三個海鳥和海狗繁衍的棲地

And this is a map of that habitat

這是棲地的地圖

that we made making maps of food

這是一張依據傳統方法

the way we've always made maps of food.

所繪製出的食物分布圖

This is how many krill are in this area of the ocean.

顯示這海域內有多少的磷蝦

Red areas represent lots of krill

紅色區域有豐富的磷蝦

and purple basically none.

而紫色代表幾乎沒有

And you can see that around the northern two most islands,

你們可以看到最北邊

which are highlighted with white circles

被圓圈標示的

because they are so tiny,

兩座小島周圍

it looks like there's a lot of food to be eaten.

看起來食物充沛

And yet, the fur seals and birds on these islands

但是島上的海狗和海鳥

are crashing.

正在減少

Their populations are declining

儘管數十年來的保育

despite decades of protection.

牠們的族群依然在縮小

And while on that southern island

而在南方的小島

at the very bottom of the screen

就是地圖下方的那座

it doesn't look like there's anything to eat,

看起來十分貧脊

those populations are doing incredibly well.

但是島上生物卻未減少

So this left us with a dilemma.

這讓我們面臨一個難題

Our observations of food don't make any sense

我們對食物分佈的觀察

in the context of our observations of these animals.

和動物的狀況不服

So we started to think about how we could do this differently.

我們開始思考要換其他方法

And this map shows not how many krill there are,

這張圖不顯示磷蝦個體數

but how many clumps of krill there are,

而是顯示有幾群磷蝦

how aggregated are they.

也就是牠們集中的程度

And what you get is a very different picture of the landscape.

結果你得到了一張完全不同的圖

Now that southern island looks

現在南方小島

like a pretty good place to be,

看起來是個不錯的地方

and when we combine this

當我們結合

with other information about prey,

關於掠食者的資訊

it starts to explain the population observations.

就可以解釋族群上的觀察結果

But we can also ask that question differently.

但我們也可以用不同角度問問題

We can have the animals tell us what's important.

我們藉由標記並追蹤動物

By tagging and tracking these animals

以瞭解什麼是關鍵因子

and looking at how they use this habitat,

看看牠們如何使用棲地資源

we are able to say, "What matters to you?"

我們就可以解釋

about the prey.

獵物對掠食者的影響

And what they've told us

而這項觀察告訴我們

is that how many krill there are really isn't important.

磷蝦個體數並不重要

It is how closely spaced those krill are

重要的是牠們有多集中

because that's how they are able to make a living.

因為牠們是掠食者賴以為生的食物

We see the same pattern

我們在不同海域

when we look in very different ocean,

觀察到相同的模式

further south in the Pacific,

包含太平洋的南端

in the warm waters around the Hawaiian islands.

被溫暖海水圍繞的夏威夷群島

So a very different habitat,

這是個截然不同的棲地

and yet the same story.

但卻訴說著相同的故事

Under some conditions,

在某一些

the physics and the nutrients, the fertilizer,

物理、營養、肥料條件下

set up aggregations in the plants, the phytoplankton.

會造成浮游植物的集中

And when that happens,

這時候

these very dense aggregations of phytoplankton

密集的浮游植物

attract their predators,

吸引了掠食者

which themselves form very dense layers.

這些浮游植物形成了密密麻麻的層次

That changes the behavior and distribution

這對更高級掠食者的

of their predators as well,

行為、分佈造成影響

starting to set up how this entire ecosystem functions.

也塑造生態系運作的特性

Finally, the predators that eat

最終，那些吃

these small fish, shrimp, and squid,

小魚、小蝦或烏賊

we're talking about two- to three-inch long prey here,

這種 2 到 3 英呎長獵物的掠食者

changes how they use their habitat

改變牠們搜尋、利用

and how they forage.

棲地資源的方式

And so we see changes in the spinner dolphins

我們看到飛旋海豚行為改變（spinner dolphins）

that are related to the changes

這些改變源自於

we're seeing in the plant life.

浮游植物的改變

And just by measuring the plants,

藉由測量浮游植物數量

we can actually predict very well

我們可以預測

what's going to happen in the top predator

食物鏈往上三層

three steps away in the food web.

那些高級掠食者的行為

But what's interesting is

但有趣的是

that even the densest aggregations of their prey

飛旋海豚仍不足以

aren't enough for spinner dolphins to make it.

依賴這種密度的獵物存活

It's a pretty tough life there in the ocean.

在海中生活很困苦

So these animals actually work together

所以動物會密切合作

to herd their prey into even denser aggregations,

將最初找到的獵物群

starting with patches that they find in the first place.

驅趕成更密集的形式

And that's what you're going to see in this visualization.

你們從這張動畫中可以看到

We have a group of 20 dolphins,

上面有 20 隻海豚

you notice they're all set up in pairs,

你會看到牠們會兩兩一組

that are working together

並通力合作

to basically bulldoze prey

驚嚇、驅趕

to accumulate it on top of itself.

使獵物群更緊密

And once they do that,

一但達成目標

they form a circle around that prey

牠們會繞著獵物群打轉

to maintain that really dense patch

迫使其保持密集

that is a couple thousand times higher density

這和最早的獵物群相較

than the background that they started with

密度多出數千倍

before individual pairs of dolphins

接著成對的海豚

start to take turns feeding

會依序進入

inside this circle of prey that they've created.

牠們集中的獵物群中進食

And so, this work is showing us

這個結果告訴我們

that animals can first give us the answers

動物行為讓我們知道

that aggregation is critical to how they make their living.

獵物密集程度和牠們能否存活有關

And by looking more deeply at the ocean,

若往更深的海底看

we're starting to understand our interactions with it

我們開始瞭解我們對海洋生物的影響

and finding more effective ways of conserving it.

藉此找出更有效的保育方法

Thank you.

謝謝