2006年考研英语 阅读真题 第3篇: Over fishing |
考研英语阅读真题
1 / 3
They have looked at half a century of data from fisheries around the world.
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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.
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Now something similar could be happening in the oceans.
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What researchers such as Ransom Myers and Boris Worm have shown is just how fast things are changing.
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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,
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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.
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but rather changes in that biomass over time.
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According to their latest paper published in Nature,
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That the seas are being overfished has been known for years.
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In some long-fished areas, it has halved again since then.
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Smaller species survived.
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The large, slow-growing animals were easy game, and were quickly hunted to extinction.
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2006年考研英语 阅读真题 第3篇: Over fishing |
考研英语阅读真题
2 / 3
Today's vessels can find their prey using satellites and sonar, which were not available 50 years ago.
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One reason for this is that fishing technology has improved.
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Dr. Worm acknowledges that these figures are conservative.
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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.
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In the early days, too, longlines would have been more saturated with fish.
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Furthermore, in the early days of longline fishing, a lot of fish were lost to sharks after they had been hooked.
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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.
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That is no longer a problem, because there are fewer sharks around now.
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They believe the data support an idea current among marine biologists, that of the "shifting baseline."
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Dr. Myers and Dr. Worm argue that their work gives a correct baseline, which future management efforts must take into account.
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2006年考研英语 阅读真题 第3篇: Over fishing |
考研英语阅读真题
3 / 3
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.
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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.
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Most fisheries are well below that, which is a bad way to do business.
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