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英['lɪs(ə)n] 美['lɪsn]
vi. 听,倾听;听从,听信
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草莓小菇凉:说的非常好,十分有道理,棒棒棒!

06-08 15:44:55

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TPO 40-L2 .Cape Cod 点击收藏

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    Listen to part of a lecture in an Environmental Conservation class.

    Next I want to talk about the collapse of the North American Cod population.

    Let's look at Cape Cod in the northeastern United States.

    the area was named Cape Cod because there was so many Cod fish in the waters just off its shores,

    so many that the first Europeans who fished there in the 17th century reported it was better than in New Finland, Canada.

    At that time, New Finland's Cod fishery was so rich that people said it was possible just to lower a bucket in the water,

    pull it out and it would be full of cod,

    but Cape Cod was even better,

    so the fishing industry there did great until after the 1940s. Uh, there were simply too many fishing vessels,

    sophisticated vessels, competing for fewer and fewer fish.

    In the 1940s there were still about four hundred million pounds of fish caught at Cape Cod every year.

    Just 50 years later though, by the 1990s,

    commercial cod fishing there had become unprofitable.

    The annual catch had gone down about 5% of its 1940s' level.

    And here's what's so fascinating:

    as more and more fishing vessels with better and better fishing technology were competing for cod,

    this competition was causing changes to the biology of the fish and these changes were making it more and more difficult for the cod population to sustain itself.

    Changes to the biology of the fish?

    Well, if a cod fish could reproduce earlier than usual,

    it'd have a better chance of passing on its genes to the next generation before being caught, right?

    And sure enough, biologists noticed that around Cape Cod,

    the cod were beginning to mature at an earlier age than normal.

    Prior to the population collapse, cod usually took about 8 to 10 years to fully mature, to start to reproduce,

    and they lived around 40 years total.

    So cod had about 30 years of active reproductive life.

    But now, cod were beginning to reproduce at a younger age, at 3 to 4 years old,

    and they were living shorter lives because they were being caught,

    so they had fewer years within which to reproduce.

    Additionally, even though some fish in the population were maturing at an earlier age,

    none was actually growing faster.

    No cod has a way of speeding up its rate of growth.

    So the younger reproductive age actually meant that smaller fish were reproducing.

    And when you're a small cod reproducing,

    you produce fewer eggs than a large cod.

    The smaller cods simply don't have the body mass to reproduce as many eggs.

    The overfishing pressure on the cod population was pushing the cod into an evolutionary corner.

    They were having a harder and harder time surviving.

    But what can be done to prevent other scenarios like this?

    I mean obviously we need a better way to manage environmental resources.

    Well, what do you guys suggest? Carol?

    Hmm, uh, maybe privatize the resource?

    A private owner would want to manage the resource efficiently in a sustainable way.

    Ok, but the problem is privatization doesn't necessarily result in better management of an environmental resource.

    Any ideas why it wouldn't?

    Well, an individual owner might not properly assess the limits of the resource.

    So they could be just as prone to overexploiting that resource as a group where lots of people have access to it.

    Yes. Well, like in the 1970s,

    when it was already clear the North American cod population was declining dramatically,

    the US and Canada declared a 200-mile exclusive economic zone in the waters around Cape Cod.

    By declaring an exclusive economic zone, you see,

    these two countries were trying to extend their territorial waters.

    Basically it was as if they were saying: 'we're the private owners. We own these waters. So we own the rights to the fish in them too.

    Essentially the two countries told fishing vessels, trollers from all other nations, to get out of the cod fishing area.

    You'd think that would be good news for the cod because there'd be less fishing.

    However, The US and Canada wanted to expel foreign trollers only in order to increase the number of their own fishing fleets.

    The total number of fishing trawlers actually increased.

    Another possible solution, pass laws that regulate use of the resource.

    But for regulation to be effective, penalties for breaking the law have to be large enough to deter violators.

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