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When prehistoric man arrived in new parts of the world, something strange happened to the large animals: they suddenly became extinct.
當史前的人到達世界的一個新的地方時，那里的大部分動物就會發生奇怪的事情，它們突然滅絕了。
Smaller species survived.
小部分動物種族存活了下來。
The large, slow-growing animals were easy game, and were quickly hunted to extinction.
但大部分的，成長緩慢的動物則成了狩獵的目標，并且很快被狩獵到滅絕。
Now something similar could be happening in the oceans.
現在相類似的事情發生在大海中.
That the seas are being overfished has been known for years.
這些年在海中的捕撈活動太過頻繁。
What researchers such as Ransom Myers and Boris Worm have shown is just how fast things are changing.
就像 Ransom Myers 和 Boris Worm 這些年所研究的，事物在迅速地變化著。
They have looked at half a century of data from fisheries around the world.
他們研究了半個世紀以來世界上所有的魚場。
Their methods do not attempt to estimate the actual biomass (the amount of living biological matter) of fish species in particular parts of the ocean,
他們的方法不是為了試圖估算特定區域的海洋中實際動物總數（活著生物的總數），
but rather changes in that biomass over time.
而是研究單位面積中海洋生物數量的變化。
According to their latest paper published in Nature,
根據他們最近在《自然》雜志上發表的文章，
the biomass of large predators (animals that kill and eat other animals) in a new fishery is reduced on average by 80% within 15 years of the start of exploitation.
大型食肉的海洋 生物（一種捕殺獵食其它動物的生物）的總量在 15 年的時間里已經減少了平均 80%。
In some long-fished areas, it has halved again since then.
在一些大型的捕魚場，這個數量已經減半。
Dr. Worm acknowledges that these figures are conservative.
Worm 博士承認這些數字還只是保守數字。
One reason for this is that fishing technology has improved.
一個原因是今天的捕魚技術已經大大改善。
Today's vessels can find their prey using satellites and sonar, which were not available 50 years ago.
可以通過衛星和聲波來發現獵物。這些在50年前是不可能的。
That means a higher proportion of what is in the sea is being caught, so the real difference between present and past is likely to be worse than the one recorded by changes in catch sizes.
這意味著同50年前相比可以捕獲更多的海洋生物，所以現在和過去的真正差距可能會比之前在捕獲區記錄的數據所顯示的更糟糕。
In the early days, too, longlines would have been more saturated with fish.
在早期的時候，多勾的魚桿線已經對魚不起作用了。
Some individuals would therefore not have been caught, since no baited hooks would have been available to trap them, leading to an underestimate of fish stocks in the past.
因此有一些魚種沒被抓到，往后沒有魚餌的魚鉤根本捕不到魚，導致過去的捕魚業受到輕視。
Furthermore, in the early days of longline fishing, a lot of fish were lost to sharks after they had been hooked.
而且，早期用魚鉤捕魚的日子， 有許多魚在它們上鉤后被鯊魚給吃了。
That is no longer a problem, because there are fewer sharks around now.
那不再是個問題，因為現在鯊魚已經很少了。
Dr. Myers and Dr. Worm argue that their work gives a correct baseline, which future management efforts must take into account.
Dr. Myers 和 Dr. worm 聲稱說，他們的工作已經確定了一個正確的基本方針，這個方針是未來管理中必須要使用的。
They believe the data support an idea current among marine biologists, that of the “shifting baseline.”
他們認為數據恰恰體現了一個海洋生物學家都支持的觀點。這個觀點就是“改變基線”。
The notion is that people have failed to detect the massive changes which have happened in the ocean because they have been looking back only a relatively short time into the past.
這個概念就是說人們已經很難觀察得到大范圍海洋中發生的變化，因為他們只是回顧從過去以來相對短的時間。
That matters because theory suggests that the maximum sustainable yield that can be cropped from a fishery comes when the biomass of a target species is about 50% of its original levels.
這確有其事，因為理論告訴我們如果一個漁場的總儲量如果連起初的最大可承受的捕魚量的50％都不到，就應該降低捕魚數量了。
Most fisheries are well below that, which is a bad way to do business.
大多數漁場遠遠低于這個數，這是對以后的捕魚業非常不利的。
