VOA慢速英语--科学家估算世界上最大鱼的年龄

Scientists have recently discovered how to compute¹ the age of whale sharks, Earth's largest fish.

Researchers used information about radioactivity levels from Cold War-era atomic bomb testing. They determined² that bands form in the shark vertebrae every year, like a tree's growth rings.

They reached their conclusion by measuring levels of carbon-14. The naturally occurring radioactive element is also a product of nuclear explosions.

It was already known that these bands existed and increased in number as sharks aged³. But it was unclear whether new rings appeared yearly or every six months.

The researchers compared carbon-14 levels in the rings to data on changes in carbon-14 levels over time. They compared them, especially, to the years of atmospheric⁴ nuclear tests in the 1950s and 1960s.

Joyce Ong is a marine⁵ scientist at Rutgers University in New Jersey⁶. She was the lead author of the study that was published recently in the journal Frontiers in Marine Science.

"These elevated levels of carbon-14 first saturated⁸ the atmosphere, then oceans and moved through food webs into animals, producing elevated levels in structures such as the vertebrae of whale sharks," Ong said.

Whale sharks have a brownish-grayish color on the back and sides with white spots. The largest ones measure some 18 meters in length. They swim great distances through the world's tropical oceans to find food and feed on small organisms taken out of the water.

The discovery enables scientists to measure a whale shark's age after its death. But just as importantly, it shows that these endangered marine giants grow slowly.

Mark Meekan, a co-author, is with the Australian Institute of Marine Science in Perth. He said, "For the management of any marine species, knowledge of growth rate is critical as it determines the resilience of populations to threats such as fishing."

Meekan said, "We thought that it was possible that they could reach ages of as much as 100 years, but we weren't really sure..."

The researchers tested carbon-14 levels in long-dead whale sharks whose remains⁹ were stored in laboratories. The oldest one tested, stored in Pakistan, had lived 50 years.

I'm John Russell.

Words in This Story

vertebrae – n. one of the small bones that are linked together to form the backbone¹⁰

data -- n. facts or information used usually to calculate, analyze¹¹, or plan something

atmospheric -- adj. of or relating to the atmosphere of the Earth or another planet

elevated -- adj. higher than normal

saturate⁷ – v. to fill (something) completeljy with something

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

resilience – n. the ability to become strong, healthy, or successful again after something bad happens

1 compute   

v./n.计算，估计

参考例句：

• I compute my losses at 500 dollars.我估计我的损失有五百元。
• The losses caused by the floods were beyond compute.洪水造成的损失难以估量。

2 determined   

adj.坚定的；有决心的

参考例句：

• I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
• He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。

3 aged   

adj.年老的，陈年的

参考例句：

• He had put on weight and aged a little.他胖了，也老点了。
• He is aged,but his memory is still good.他已年老，然而记忆力还好。

4 atmospheric   

adj.大气的，空气的；大气层的；大气所引起的

参考例句：

• Sea surface temperatures and atmospheric circulation are strongly coupled.海洋表面温度与大气环流是密切相关的。
• Clouds return radiant energy to the surface primarily via the atmospheric window.云主要通过大气窗区向地表辐射能量。

5 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。

6 jersey   

n.运动衫

参考例句：

• He wears a cotton jersey when he plays football.他穿运动衫踢足球。
• They were dressed alike in blue jersey and knickers.他们穿着一致，都是蓝色的运动衫和灯笼短裤。

7 saturate   

vt.使湿透，浸透；使充满，使饱和

参考例句：

• We'll saturate California with the rise in its crime rate.我们将使加利福尼亚州的犯罪案件增长率达到饱和点。
• Saturate the meat in the mixture of oil and herbs.把肉浸泡在油和作料的卤汁里。

8 saturated   

a.饱和的，充满的

参考例句：

• The continuous rain had saturated the soil. 连绵不断的雨把土地淋了个透。
• a saturated solution of sodium chloride 氯化钠饱和溶液

9 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

10 backbone   

n.脊骨，脊柱，骨干；刚毅，骨气

参考例句：

• The Chinese people have backbone.中国人民有骨气。
• The backbone is an articulate structure.脊椎骨是一种关节相连的结构。

11 analyze   

vt.分析，解析 (=analyse)

参考例句：

• We should analyze the cause and effect of this event.我们应该分析这场事变的因果。
• The teacher tried to analyze the cause of our failure.老师设法分析我们失败的原因。