【英语时差8,16】珍稀淡水豚

 Most of us are familiar with those clever ocean dwelling¹ mammals, the dolphins. But did you know that there are a few rare species of dolphins that live exclusively in rivers?

    Sadly, one of the five species of river dolphins, the Chinese, or Yangtze River Dolphin, was declared “functionally extinct” in 2007 after intensive searches failed to locate even a single individual. The other four species, two in southern Asia and two in South America are critically endangered.

    Besides living in freshwater, river dolphins have other traits that make them unique among dolphins. The Ganges and Indus River Dolphins are almost completely blind. Their tiny eyes don’t even have lenses.

    Like their marine² cousins, river dolphins use echolocation to find prey³ and navigate⁴ around obstacles. But unlike oceanic dolphins, the Ganges and Indus River Dolphins rely almost entirely⁵ on echolocation to sense their surroundings. In the murky⁶ dark waters in the rivers where they live, sight wouldn’t be much use anyway.

    The Amazon River Dolphin, or Boto, also has special traits to help it live in rivers. It can turn its head! The neck vertebrae of all other dolphins are fused. If they want to see an object beside or below them, they must orient their whole body in that direction.

    The Boto’s flexible neck allows it to hunt and move more easily in narrow waterways. The Boto also has stiff hairs along its long snout. The sensitive hairs help it detect prey in muddy river bottoms.

    These beautiful and unique creatures face an ever increasing threat of extinction⁷ due to habitat loss, hunting by humans, underwater noise pollution, river damming, and lethal⁸ encounters with boats or fishing nets.

1 dwelling   

n.住宅，住所，寓所

参考例句：

• Those two men are dwelling with us.那两个人跟我们住在一起。
• He occupies a three-story dwelling place on the Park Street.他在派克街上有一幢3层楼的寓所。

2 marine   

adj.海的；海生的；航海的；海事的；n.水兵

参考例句：

• Marine creatures are those which live in the sea. 海洋生物是生存在海里的生物。
• When the war broke out,he volunteered for the Marine Corps.战争爆发时，他自愿参加了海军陆战队。

3 prey   

n.被掠食者，牺牲者，掠食；v.捕食，掠夺，折磨

参考例句：

• Stronger animals prey on weaker ones.弱肉强食。
• The lion was hunting for its prey.狮子在寻找猎物。

4 navigate   

v.航行，飞行；导航，领航

参考例句：

• He was the first man to navigate the Atlantic by air.他是第一个飞越大西洋的人。
• Such boats can navigate on the Nile.这种船可以在尼罗河上航行。

5 entirely   

ad.全部地，完整地；完全地，彻底地

参考例句：

• The fire was entirely caused by their neglect of duty. 那场火灾完全是由于他们失职而引起的。
• His life was entirely given up to the educational work. 他的一生统统献给了教育工作。

6 murky   

adj.黑暗的，朦胧的；adv.阴暗地，混浊地；n.阴暗；昏暗

参考例句：

• She threw it into the river's murky depths.她把它扔进了混浊的河水深处。
• She had a decidedly murky past.她的历史背景令人捉摸不透。

7 extinction   

n.熄灭，消亡，消灭，灭绝，绝种

参考例句：

• The plant is now in danger of extinction.这种植物现在有绝种的危险。
• The island's way of life is doomed to extinction.这个岛上的生活方式注定要消失。

8 lethal   

adj.致死的；毁灭性的

参考例句：

• A hammer can be a lethal weapon.铁锤可以是致命的武器。
• She took a lethal amount of poison and died.她服了致命剂量的毒药死了。