VOA慢速英语2021--鲨鱼会利用地球磁场导航

Scientists have found that sharks use the Earth's magnetic field as a sort of natural GPS. This permits them to swim across great distances in the world's oceans.

GPS, or Global Positioning System, is a United States government-owned service that provides users with their location on Earth. A GPS device can tell users directions from any point to another point in real-time.

Researchers held experiments with a small kind of shark in a sea laboratory. They confirmed the theory that sharks use magnetic fields to guide their travels. This behavior is seen in other sea animals as well. Their study was published this month in the journal Current Biology.

Bryan Keller, an expert on sea life, is one of the researchers. He said the study explained how sharks can travel the seas and find their way back to feed and produce offspring¹.

Keller said, "We know that sharks can respond to magnetic fields." But scientists did not know that they use magnetic fields to help direct them. He noted² that "You have sharks that can travel 20,000 kilometers and end up in the same spot."

Researchers have questioned how sharks perform long-distance traveling for years. Sharks make their trips in the open ocean where they pass few physical features such as corals that could serve as landmarks³.

Looking for answers, scientists based at Florida State University decided⁴ to study a small kind of shark called a bonnethead. The bonnethead shark they studied lives on both American coasts and returns to the same waters every year.

Researchers created magnetic conditions to make 20 bonnethead sharks think they were hundreds of kilometers away from where they were caught off Florida. The scientists found that the sharks began to swim north. This was due to the magnetic conditions that made them think they were south of where they should be.

Robert Hueter, who was not involved with the study, is a scientist at Mote⁵ Marine⁶ Laboratory & Aquarium⁷. Hueter said more studies are needed to find out how the sharks use magnetic fields to know their location. Also, studies are needed to find out if larger, long-distance traveling sharks use a similar system to find their way.

He said the question has always been: if sharks are sensitive to magnetic fields, do they use this sense to travel the oceans and how? He said the researchers are making some progress at answering this question.

Keller said the study could help inform the protection of certain sharks. A study this year found that the number of sharks dropped more than 70 percent between 1970 and 2018.

Researchers say that, like bonnetheads, other sharks probably also use the Earth's magnetic field. This includes large sharks that make cross-ocean trips. Keller said that it is very unlikely that the shark they studied developed this sense and other traveling sharks did not.

Words in This Story

shark – n. a large and often dangerous sea fish with very sharp teeth

offspring – n. the young of an animal or plant

respond – v. to do something as a reaction to something that has happened or been done

spot – n. a particular space or area

location – n. a place or position

sensitive – adj. able to sense very small changes in something

1 offspring   

n.子女，子孙，后代，（动物的）崽

参考例句：

• Jack is her only offspring.杰克是她唯一的后代。
• This device is the offspring of his inventive mind.这一装置是他那长于发明的头脑的产儿。

2 noted   

adj.著名的，知名的

参考例句：

• The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。
• Jim is noted for arriving late for work.吉姆上班迟到出了名。

3 landmarks   

n.陆标( landmark的名词复数 )；目标；（标志重要阶段的）里程碑 ~ (in sth)；有历史意义的建筑物（或遗址）

参考例句：

• The book stands out as one of the notable landmarks in the progress of modern science. 这部著作是现代科学发展史上著名的里程碑之一。 来自《现代汉英综合大词典》
• The baby was one of the big landmarks in our relationship. 孩子的出世是我们俩关系中的一个重要转折点。 来自辞典例句

4 decided   

adj.决定了的，坚决的；明显的，明确的

参考例句：

• This gave them a decided advantage over their opponents.这使他们比对手具有明显的优势。
• There is a decided difference between British and Chinese way of greeting.英国人和中国人打招呼的方式有很明显的区别。

5 mote   

n.微粒；斑点

参考例句：

• Seeing the mote in one's neighbor's eye,but not the beam in one's own.能看见别人眼里的尘埃，看不见自己眼里的木头。
• The small mote on her forehead distinguishes her from her twin sister.她额头上的这个小斑点是她与其双胞胎妹妹的区别。

6 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。

7 aquarium   

n.水族馆，养鱼池，玻璃缸

参考例句：

• The first time I saw seals was in an aquarium.我第一次看见海豹是在水族馆里。
• I'm going to the aquarium with my parents this Sunday.这个星期天，我要和父母一起到水族馆去。