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历年考研英语阅读理解2006年03

所属教程:历年考研英语阅读理解

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[00:05.82]2006 Text3

[00:08.14]When prehistoric man arrived in new parts of the world,

[00:12.17]something strange happened to the large animals:

[00:15.51]they suddenly became extinct.

[00:18.03]Smaller species survived.

[00:20.54]The large, slow-growing animals were easy game,

[00:24.07]and were quickly hunted to extinction.

[00:27.09]Now something similar could be happening in the oceans.

[00:31.42]That the seas are being overfished

[00:33.96]has been known for years.

[00:36.18]What researchers such as Ransom Myers

[00:38.95]and Boris Worm have shown

[00:40.86]is just how fast things are changing.

[00:43.79]They have looked at half a century of data

[00:46.92]from fisheries around the world.

[00:49.46]Their methods do not attempt to estimate the actual biomass

[00:53.68](the amount of living biological matter)

[00:56.48]of fish species in particular parts of the ocean,

[00:59.86]but rather changes in that biomass over time.

[01:03.98]According to their latest paper published in Nature,

[01:07.50]the biomass of large predators

[01:10.04](animals that kill and eat other animals)

[01:12.96]in a new fishery is reduced on average by 80%

[01:17.37]within 15 years of the start of exploitation.

[01:21.42]In some long-fished areas,

[01:23.52]it has halved again since then.

[01:26.55]Dr. Worm acknowledges that these figures are conservative.

[01:31.20]One reason for this is that fishing technology has improved.

[01:35.83]Today's vessels can find their prey using satellites and sonar,

[01:41.07]which were not available 50 years ago.

[01:44.91]That means a higher proportion of

[01:47.23]what is in the sea is being caught,

[01:49.86]so the real difference between present and past

[01:52.88]is likely to be worse than the one recorded

[01:55.14]by changes in catch sizes.

[01:58.68]In the early days, too, longlines would have been

[02:01.68]more saturated with fish.

[02:03.88]Some individuals would therefore not have been caught,

[02:07.21]since no baited hooks would have been available to trap them,

[02:10.93]leading to an underestimate of fish stocks in the past.

[02:15.28]Furthermore, in the early days of longline fishing,

[02:18.90]a lot of fish were lost to sharks after they had been hooked.

[02:23.05]That is no longer a problem,

[02:25.36]because there are fewer sharks around now.

[02:28.78]Dr. Myers and Dr. Worm argue

[02:31.33]that their work gives a correct baseline,

[02:34.13]which future management efforts must take into account.

[02:38.47]They believe the data support an idea current

[02:41.70]among marine biologists,

[02:43.71]that of the "shifting baseline".

[02:46.13]The notion is that people have failed to detect

[02:48.26]the massive changes which have happened in the ocean

[02:51.69]because they have been looking back

[02:53.14]only a relatively short time into the past.

[02:57.07]That matters because theory suggests

[02:59.49]that the maximum sustainable yield

[03:01.61]that can be cropped from a fishery comes

[03:04.13]when the biomass of a target species

[03:06.77]is about 50% of its original levels.

[03:10.36]Most fisheries are well below that,

[03:13.00]which is a bad way to do business.

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