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第1段
1 .Well, ongoing investigations have revealed that predation is the most likely cause of sea otter decline after all.
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2 .First, the pollution theory is weakened by the fact that no one can really find any dead sea others washing off on Alaskan beaches.
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3 .That's not what you would expect if infections caused by pollution started killing a lot of otters.
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4 .On the other hand, the fact that it's so hard to find dead otters is consistent with the predator hypothesis.
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5 .If an otter is killed by a predator, it's eaten immediately so it can't wash up on shore.
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6 .Second, although orcas may prefer to hunt whales, whales have essentially disappeared from the area because of human hunters.
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7 .That means that orcas have had to change their diet to survive and since only smaller sea mammals are now available, orcas have probably started hunting those.
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8 .So it probably is the orcas that are causing the decline of all the smaller sea mammals mentioned in the passage - the seals, the sea lions and the sea otters.
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9 .And third, the uneven pattern of otter decline is better explained by the orca predation theory than by the pollution theory.
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10 .What happens to otters seems to depend on whether the location where they live is accessible to orcas or not.
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11 .In those locations that orcas can access easily, the number of sea otters has declined greatly.
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12 .However, because orcas are so large, they can't access shallow or rocky locations.
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13 .And shallow and rocky locations are precisely the types of locations where sea otter populations have not declined.
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