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Now listen to part of a lecture on the topic you just read about.
現在來聽一段有關你剛剛聽到的話題的演講。
The truth is we don't know what the main cause of extinction of Steller's sea cow was.
真實的情況是，我們并不知道虎頭海牛滅絕的主要原因是什么。
There are problems with each of the theories that you read about.
閱讀中的每一個理論都是存在一些問題的。
First, the sea cows were massive creatures.
首先，海牛是非常龐大的生物。
They were up to nine meters long and could weigh over ten tons, just enormous.
它們通常都會達到9米長，而且重達10噸，體型巨大。
A couple of sea cows could feed a small Siberian village for months.
幾個海牛就夠一個西伯利亞小村莊吃幾個月了。
And the population of the native Siberian people wasn't very large.
況且西伯利亞本地人的人口也不是很大。
So while the Siberians certainly did hunt the sea cows, they didn't need to hunt a lot of them.
所以就算是西伯利亞人當時的確捕殺了海牛，那他們也不會捕很多。
So it's unlikely they were the ones who brought the sea cows to the point of extinction.
由此看來他們并不是造成海牛滅絕的原因。
Second, about a hypothetical decrease in kelp caused by ecological disturbances.
其次是關于生態干擾造成的海藻減少的這個假設。
Well, if something severe really happened in the ecosystem near Bering Island sometime before 1768,
如果說1768年之前，白令島附近真的發生了嚴重的生態問題，
it would have affected not just the kelp, but also other parts of the ecosystem.
那么這個問題所影響的就不僅僅是海藻了，生態系統里的其他生物一定也會受到影響。
For example, it would have caused the decline in other marine animals, like whales.
比如說它就會造成其他海洋動物，像鯨魚數量的下降。
But fishing ships in the area did not report a whale decline.
但是該地區的捕魚船只并沒有給出鯨魚數量下降的報告。
Since there is no indication of broader ecosystem problems, the kelp was probably growing just fine, and the sea cows did not experience food shortage.
由于并沒有更廣泛的生態問題，海藻很可能就生長的很好并且海牛也沒有經歷食物短缺。
Third, it might seem like the European traders were responsible because the sea cows became extinct soon after the Europeans arrived.
第三，因為海牛在歐洲人到來不久就滅絕了所以歐洲商人的這個理由看起來似乎看起來挺合理的。
But, actually, by the time that the Europeans arrived, the sea cow population was already quite small.
但是實際上，在歐洲人到來之前海牛的數量已經非常的小了。
We have evidence that the sea cow population was at its largest hundreds of years before the 1700s.
現在有證據表明海牛在16世紀之前的數量達到了它的頂峰。
So something was causing a serious and on-going decrease in the sea cow population long before Europeans arrived in the Bering Island area.
所以在歐洲人到達白令島之前，一定有一個東西引起了海牛數量嚴重、持續的下降。
Whatever this something was, it should be considered the main cause of the extinction, not the European traders who were just the last to arrive.
不管這個東西是什么，它都應該是海牛滅絕的主要原因，而不是歐洲商人。
