墨尔本PTE素材库——This Shark Is the Vertebrate Methuselah

墨尔本PTE素材库——This Shark Is the Vertebrate Methuselah

中文批注

这段Podcast主题是格陵兰岛一种长寿的鲨鱼，科学家们对它们并没有太多了解，但研究表明它们的寿命非常长，作为研究对象的这条鲨鱼就至少活了390岁，而考虑到研究存在的误差，它也有可能已经活了500岁以上。

澳大利亚语言学院整理的PTE素材库，旨在用最贴近PTE Official Question Criteria的材料，给大家提供一系列不同话题的PTE素材！让大家可以在平时练习听力、阅读、口语、写作，不至于陷入“题荒”的境地！

这段材料有大量的科学词汇，科技类词汇薄弱的同学赶紧累积起来！可以用于练习Dictation和Re-tell Lecture，不怕难的同学也可以试试Summarize spoken/written text，不过这段材料作为这PTE考试的两个题型的练习难度就有些高了。

【Key Vocabulary】

vertebrate n. 脊椎动物

longevity n. 寿命，长寿

tortoise n. 乌龟

Bowhead whale 北极露脊鲸

conservative adj. 保守的

marine biologist 海洋生物学家

vessel n. 小船，舰

observation n. 观察

investigate v. 调查，研究

gauging n. 测定，测量

radiocarbon dating 放射性碳测定年代法，碳同位素年龄测定

uncertainty n. 不确定性

upper limit 上限

sexual maturity 性成熟

bycatch n. 渔获物

inadvertently  adv. 非故意的，无心的

adolescence n. 青春期

Full Transcript

Individual Greenland sharks appear to live perhaps a century longer than any other vertebrate, and might have life spans approaching 500 years.

By human standards, a few vertebrate species have incredible longevity. Some tortoises live for nearly 200 years. Bowhead whales can live even a decade or two longer. But now there’s a new champion: the Greenland shark—which conservative estimates have swimming in the seas for almost three centuries.

Julius Nielsen is a marine biologist and PhD student at the University of Copenhagen. While on a research vessel in Greenland where such sharks were accidentally caught, Nielsen became curious about the creatures.

“And perhaps the biggest of all the mysteries were how long do these sharks actually live. Because it has been expected that they can get very old, and that’s based on some observations of very, very slow growth…so the longevity could be exceptional and extreme, but it has just never been possible to investigate.”

That’s because Greenland sharks don’t have the same body structures used for gauging the age of most fish or even other sharks. So Neilsen and colleagues used a new technique based on the lens of the eye. The centers of the lenses can be analyzed by radiocarbon dating to determine about when the shark was born. They tested 28 female sharks.

“And what we found was that the biggest shark in our analysis, and also the oldest shark, was estimated—the most likely single year age was almost approximately 390 years.”

Nielsen stresses that the estimate contains a fair amount of uncertainty. Though the likeliest age is 390, the shark could be as young as a mere 272. “That still makes the Greenland shark the longest-living vertebrate known to science.” And at the upper limit, it’s possible that the shark is more than 500 years old. The study is in the journal Science. [Link to come]

Also shocking: the researchers estimate that the sharks live at least a century before they reach sexual maturity. “And of course it is absolutely amazing and difficult for a human mind to understand that sexual reproduction begins so late in life.”

In the paper Nielsen and his colleagues stress the importance of caution and conservation. “And the thing about Greenland sharks is just we don’t know how many sharks are out there. But it’s clear that if you reach sexual maturity above 100 years then you are potentially sensitive to any kind of high bycatch rate and any kind of future commercial exploitations.”

With a century to do it, humans could inadvertently wipe out the entire next generation of these sharks during their long, slow adolescence.

—Cynthia Graber

(Source: http://www.scientificamerican.com/podcast/episode/this-shark-is-the-vertebrate-methuselah/)