VOA慢速英语--鲨鱼数量自1970年以来下降了71%

Scientists have known for decades that the numbers of some shark species¹ are decreasing. But a new study shows just how severely² worldwide populations have dropped in the past 50 years.

The numbers of oceanic sharks and rays fell more than 70 percent worldwide between 1970 and 2018. The information comes from a study that appeared recently in the publication Nature.

Stuart Sandin is a marine³ biologist who works at the Scripps Institution of Oceanography. He says that sharks are great hunters, fast swimmers and have extraordinary senses.

Sandin adds that they can identify any changes in the ocean from a great distance, such as smells or tiny changes in water flow.

Their ability to quickly sense anything outside the norm⁴ in their environment helps them find food in the open ocean. But it also makes them especially at risk in the face of increased international fishing pressure.

"You drop a fishing line in the open ocean, and often it's sharks that are there first — whether or not they're the primary target," said Sandin.

Twenty-four of the 31 species of sharks and rays are threatened with extinction⁵. Three species — oceanic whitetip sharks, scalloped hammerhead sharks and great hammerhead sharks — are considered critically endangered.

Nathan Pacoureau is a biologist at Simon Fraser University in Canada and one of the writers of the study. He said, "The last 50 years have been pretty devastating⁶ for global shark populations."

Sometimes sharks are caught on purpose by fishing boats. But more often they are caught while fishing for other species such as tuna and swordfish.

Sharks and rays are both fish with skeletons⁷ made of cartilage, not bone. Unlike most other kinds of fish, they are not able to reproduce⁸ for several years, and also produce fewer young.

Pacoureau said sharks reproduce more like mammals than fish, so "their populations cannot replenish⁹ as quickly as many other kinds of fish."

The number of fishing boats in the open ocean has risen sharply¹⁰ since the 1950s. Climate change and pollution also place shark survival¹¹ at risk. But increased fishing pressure is the greatest threat for every oceanic shark species.

Stuart Pimm is an ecologist at Duke University and was not involved in the study. He said the removal of top hunters like sharks from the ocean affects all sea life.

"Sharks are like the lions, tigers and bears of the ocean world, and they help keep the rest of the ecosystem¹² in balance," Pimm said.

Words in This Story

cartilage – n. a strong but flexible material found in some parts of the body (such as the nose, the outer ear, and some joints)

devastating – adj. causing great damage or harm

ecosystem – n. everything that exists in a particular environment

extinction – n. the state or situation that results when something (such as a plant or animal species) has died out completely

mammals – n. types of animals that feed milk to its young and that usually have hair or fur covering most of its skin

primary – adj. most important

replenish – v. to fill or build up (something) again

species – n. a group of animals or plants that are similar and can produce young animals or plants; a group of related animals or plants that is smaller than a genus

1 species   

n.物种，种群

参考例句：

• Are we the only thinking species in the whole of creation?我们是万物中惟一有思想的物种吗？
• This species of bird now exists only in Africa.这种鸟现在只存在于非洲。

2 severely   

adv.严格地；严厉地；非常恶劣地

参考例句：

• He was severely criticized and removed from his post.他受到了严厉的批评并且被撤了职。
• He is severely put down for his careless work.他因工作上的粗心大意而受到了严厉的批评。

3 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。

4 norm   

n.标准，规范，平均数

参考例句：

• Of his age,the child is above the norm in arithmetic.在他那个年龄，这个孩子的算术能力是超过标准的。
• These events were aberrations from the norm.这些事件不合常规。

5 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。

6 devastating   

adj.毁灭性的，令人震惊的，强有力的

参考例句：

• It is the most devastating storm in 20 years.这是20年来破坏性最大的风暴。
• Affairs do have a devastating effect on marriages.婚外情确实会对婚姻造成毁灭性的影响。

7 skeletons   

n.（建筑物等的）骨架( skeleton的名词复数 )；骨骼；梗概；骨瘦如柴的人（或动物）

参考例句：

• Only skeletons of buildings remained. 只剩下了建筑物的框架。 来自辞典例句
• It looks like six skeletons in front of that stone door! 在这石头门前看上去就象有六副骨骼！ 来自辞典例句

8 reproduce   

v.生育，繁殖，复制，重做

参考例句：

• The machine can reproduce a key in two minutes.这机器能在两分钟内复制一把钥匙。
• The picture will reproduce well.这照片会印得很清楚。

9 replenish   

vt.补充；(把…)装满；(再)填满

参考例句：

• I always replenish my food supply before it is depleted.我总是在我的食物吃完之前加以补充。
• We have to import an extra 4 million tons of wheat to replenish our reserves.我们不得不额外进口四百万吨小麦以补充我们的储备。

10 sharply   

adj.锐利地，急速；adv.严厉地，鲜明地

参考例句：

• The plane dived sharply and rose again.飞机猛然俯冲而后又拉了起来。
• Demand for personal computers has risen sharply.对个人电脑的需求急剧增长。

11 survival   

n.留住生命，生存，残存，幸存者

参考例句：

• The doctor told my wife I had a fifty-fifty chance of survival.医生告诉我的妻子，说我活下去的可能性只有50%。
• The old man was a survival of a past age.这位老人是上一代的遗老。

12 ecosystem   

n.生态系统

参考例句：

• This destroyed the ecosystem of the island.这样破坏了岛上的生态系统。
• We all have an interest in maintaining the integrity of the ecosystem.维持生态系统的完整是我们共同的利益。