2016託業考試閲讀資料：海獺數量減少的原因

阿拉斯加州的海獺數目在削減?是情形污染?仍是天敵捕食?

閲讀材料：

The sea otter is a small mammal that lives in waters along the western coast of North America from California to Alaska. When some sea otter populations off the Alaskan coast started rapidly declining a few years ago, it caused much concern because sea otters play an important ecological role in the coastal ecosystem. Experts started investigating the cause of the decline and quickly realized that there were two possible explanations: environmental pollution or attacks by predators. Initially, the pollution hypothesis seemed the more likely of the two.

海獺是一種餬口在北美西海岸從加州到阿拉斯加沿線的小型海洋哺乳動物。幾年前，阿拉斯加海岸的海獺數目急劇削減。因為海獺對於維持海岸沿線生態平衡有很是主要的浸染，所以其數目下降引起了普遍的關注。專家起頭研究海獺數目下降的原因，而且很快發現了兩個可能的原因，分袂是情形污染和天敵捕食。最初，情形污染説看起來更為可託。

The first reason why pollution seemed the more likely cause was that there were known sources of it along the Alaskan coast, such as oil rings and other sources of industrial chemical pollution. Water samples from the area revealed increased levels of chemicals that could decrease the otters’ resistance to life-threatening infections and thus could indirectly cause their deaths.

為侍趵碹染説更為可託呢?這是因為阿拉斯加海岸確實有污染源，好比石油帶或者其他的工業污染物。該地的水樣顯示水中化學物的含量增添，其數目可以導致海獺對於對於一些致命傳染損失蹤抵當力，進而借居導致數目下降。

Second, other sea mammals such as seals and sea lions along the Alaskan coast were also declining; indicating that whatever had endangered the otters was affecting other sea mammals as well. This fact again pointed to environmental pollution, since it usually affect the entire ecosystem rather than a single species. Only widely occurring predators, such as the orca (a large predatory whale), could have the same effect, but orcas prefer to hunt much larger prey, such as other whales.

第二，在阿拉斯加海域，蒐羅海豹和海獅在內的其他海洋哺乳動物的`數目也有所下降。這剖明造成海獺數目下降的原因也對其他海洋哺乳動物造成了影響。原因再次指向了情形污染，這是因為情形污染問題經常不是僅僅影響某個特定物種，而是影響整個生態系統。除此之外，只有像逆戟鯨(一種大型肉食鯨)那種食性普遍的動物才能經由過程捕食呈現不異的效不美觀。可是，逆戟鯨更喜歡捕食像鯨類這種的大型獵物。

Third, scientists believed that the pollution hypothesis could also explain the uneven pattern of otter decline: at some Alaskan locations the otter populations declined greatly, while at others they remained stable. Some experts explained these observations by suggesting that ocean currents or other environmental factors may have created uneven concentrations of pollutants along the coast.

第三，科學家認為污染説同時可以詮釋海獺數目轉變的不平衡性。所謂不平衡性是指在阿拉斯加某些區域海獺數目下交窬淘，而在其他處所海獺的數目連結不決。一些專家指出這樣的不雅察看結不美觀剖明洋流和其他情形身分導致了海岸線上污染物的不平衡聚積。

閲讀部門需要提取的不雅概念是：

- Main point: 海獺數目下降的原因是情形污染

- Sub point 1:阿拉斯加海域確有污染源

- Sub point 2:除海獺外，還有其他哺乳動物的數目下降

- Sub point 3:分歧區域海獺數目下降情形分歧，可以詮釋為污染物聚積情形分歧導致的。

聽力材料：

Well, ongoing investigations have revealed that predation is the most likely cause of sea otter decline after all.

今朝的研究剖明天敵捕食是最可能導致海獺數目削減的原因。

First, the pollution theory is weakened by the fact that no one can really find any Dead Sea otters washing off on Alaskan beaches. That’s not what you would expect if infections caused by pollution started killing a lot of otters. On the other hand, the fact that it’s so hard to find dead otters is consistent with the predator hypothesis. If an otter is killed by a predator, it’s eaten immediately so it can’t wash up on shore.

首先，因為沒有人發現有海獺屍身被衝上阿拉斯加海灘，所以污染理論捕食那麼站得住腳的。如不美觀污染造成的疾病傳染導致了海獺數目的劇減，那麼情形不應如斯。而且，很少發現海獺屍身也恰恰説了然天敵捕食假説。捕食者殺死了海獺後，會很快地吃失蹤它，那麼我們也就不會再岸上發現海獺屍身了