美国国家公共电台 NPR--Why hammerhead sharks 'hold their breath' in deeper, colder waters

Why hammerhead sharks 'hold their breath' in deeper, colder waters

Transcript¹

Research shows some hammerhead sharks hold their breath when diving deep under water. They do it to keep their bodies from getting too cold. (Story aired on All Things Considered on May 11, 2023.)

MARY LOUISE KELLY, HOST:

Sharks are among the best swimmers on the planet, but a new study in the journal Science shows that one species may be diving deep using a trick common to humans. NPR's Geoff Brumfiel has more.

GEOFF BRUMFIEL, BYLINE²: The scalloped hammerhead shark lives in oceans all over the planet.

MARK ROYER: It's one of the larger but not the largest hammerhead species.

BRUMFIEL: That's Mark Royer, a shark researcher at the University of Hawaii at Manoa. Scalloped hammerheads have a really unusual skill. They can dive to over 2,500 feet below the surface. At those depths, even the most sunny, tropical oceans become dark and frigid³.

ROYER: Imagine you're on a warm, sunny beach, and you hop⁴ out of the warm water and then immediately plunge⁵ into an ice bath.

BRUMFIEL: It'd be unpleasant for a human, but it's potentially deadly for a shark. A shark can't generate its own body heat. If it gets too cold, it can't swim. And if it stops swimming, water doesn't flow across its gills. It can't breathe. It dies. So here's the question.

ROYER: How is it that a coastal⁶, warm, tropical species is able to go down into these deep depths and survive?

BRUMFIEL: To find out, Royer and his colleagues went to a bay where the hammerheads swim.

ROYER: We do this all in a small 17-foot Boston whaler, so it's almost, like, the size of a dinghy.

BRUMFIEL: You don't think you need a bigger boat?

ROYER: We don't, no. It's like the smaller, the better because we want to be able to lean over and get as close as possible.

BRUMFIEL: In order to attach a bunch of electronics to each shark's fin⁷.

ROYER: This is essentially⁸ like putting a Fitbit on the shark.

BRUMFIEL: When Royer and his colleagues later analyzed⁹ that sharky Fitbit data, what they found amazed them. The sharks dive, spend just a few minutes at the bottom, probably hunting squid.

ROYER: And then they pitch themselves at an 80-degree angle and then shoot towards the surface.

BRUMFIEL: But what's really wild is their body temperature doesn't drop. It stays steady until they start coming back from the deep. Royer quickly realized what was going on.

ROYER: They were closing their gill slits¹⁰ and preventing that water from flowing across their gills that would cool their body down.

BRUMFIEL: They're holding their breath. The sharks are holding their breath.

ROYER: Yes, they're holding their breath.

BRUMFIEL: Remember; unlike humans, sharks use gills to breathe underwater. This is all about temperature. Passing cold water over the gills would cool the shark's blood, putting it in danger. It makes sense, Royer says, but he still can't quite believe it.

ROYER: After doing this study, it still shocks and baffles me.

BRUMFIEL: That a shark would need to hold its breath underwater. Geoff Brumfiel, NPR News.

1 transcript   

n.抄本，誊本，副本，肄业证书

参考例句：

• A transcript of the tapes was presented as evidence in court.一份录音带的文字本作为证据被呈交法庭。
• They wouldn't let me have a transcript of the interview.他们拒绝给我一份采访的文字整理稿。

2 byline   

n.署名；v.署名

参考例句：

• His byline was absent as well.他的署名也不见了。
• We wish to thank the author of this article which carries no byline.我们要感谢这篇文章的那位没有署名的作者。

3 frigid   

adj.寒冷的，凛冽的；冷淡的；拘禁的

参考例句：

• The water was too frigid to allow him to remain submerged for long.水冰冷彻骨，他在下面呆不了太长时间。
• She returned his smile with a frigid glance.对他的微笑她报以冷冷的一瞥。

4 hop   

n.单脚跳，跳跃；vi.单脚跳，跳跃；着手做某事；vt.跳跃，跃过

参考例句：

• The children had a competition to see who could hop the fastest.孩子们举行比赛，看谁单足跳跃最快。
• How long can you hop on your right foot?你用右脚能跳多远？

5 plunge   

v.跳入，(使)投入，(使)陷入；猛冲

参考例句：

• Test pool's water temperature before you plunge in.在你跳入之前你应该测试水温。
• That would plunge them in the broil of the two countries.那将会使他们陷入这两国的争斗之中。

6 coastal   

adj.海岸的，沿海的，沿岸的

参考例句：

• The ocean waves are slowly eating away the coastal rocks.大海的波浪慢慢地侵蚀着岸边的岩石。
• This country will fortify the coastal areas.该国将加强沿海地区的防御。

7 fin   

n.鳍；(飞机的)安定翼

参考例句：

• They swim using a small fin on their back.它们用背上的小鳍游动。
• The aircraft has a long tail fin.那架飞机有一个长长的尾翼。

8 essentially   

adv.本质上，实质上，基本上

参考例句：

• Really great men are essentially modest.真正的伟人大都很谦虚。
• She is an essentially selfish person.她本质上是个自私自利的人。

9 analyzed   

v.分析( analyze的过去式和过去分词 )；分解；解释；对…进行心理分析

参考例句：

• The doctors analyzed the blood sample for anemia. 医生们分析了贫血的血样。 来自《简明英汉词典》
• The young man did not analyze the process of his captivation and enrapturement, for love to him was a mystery and could not be analyzed. 这年轻人没有分析自己蛊惑著迷的过程，因为对他来说，爱是个不可分析的迷。 来自《简明英汉词典》

10 slits   

n.狭长的口子，裂缝( slit的名词复数 )v.切开，撕开( slit的第三人称单数 )；在…上开狭长口子

参考例句：

• He appears to have two slits for eyes. 他眯着两眼。
• "You go to--Halifax,'she said tensely, her green eyes slits of rage. "你给我滚----滚到远远的地方去！" 她恶狠狠地说，那双绿眼睛冒出了怒火。