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Sharks Head Straight Home by Smell 嗅觉——鲨鱼导航秘诀

Some sea creatures can find their way through thousands of miles of seemingly featureless oceans. Even more impressive is the route that they take.

一些海洋生物能够在茫茫的大海中找到方向，而最让人印象深刻的是它们的航线。

“Well, we’ve known for a long time that sharks are capable of long-distance migrations¹, and in some cases those migrations occur along very straight paths.” Scripps Institution of Oceanography biologist Andy Nosal. “And this has always begged the question: how exactly do they know where they’re going?...So, there have been a lot of hypotheses floated over the last several decades, including the idea that these sharks are using, for example, geomagnetic cues, chemical cues and others. But none of these have really been systematically² tested in the field.”

“很久以前我们就知道，鲨鱼能够长途迁移，并且在某些情况下，它们的的迁徙路线是直的。” 斯克瑞普思研究生海洋生物学家安迪·诺萨尔说到。“一直以来人们都未探讨问题的实质：鲨鱼究竟是怎样知道自己的去向呢?因此，过去几十年来，人们有无数的假设，例如鲨鱼在利用地磁信号、化学信号等等。但是，所有这些假设都尚未得到系统地检测。”

Nosal and his team suspected that the navigational secret of some sharks might be their sense of smell. They use their keen noses to find food, of course. And other fish, like salmon³, are known to use olfaction to navigate⁴.

诺萨尔和他的团队猜测，鲨鱼的导航秘诀可能是嗅觉。鲨鱼可以使用自己灵敏的鼻子来寻找食物。人们知道鲑鱼等其他鱼类利用嗅觉进行导航。

To see if his hunch⁵ was right, Nosal scooped⁶ up some adult female leopard⁷ sharks in their preferred environment, waist-deep water off the San Diego coast. He attached a small radio transmitter behind their dorsal⁸ fins⁹. And he half of the sharks by shoving cotton balls soaked with petroleum¹⁰ jelly blocked the sense of smell inin their nostrils¹¹.

为了验证猜测是否正确，诺萨尔在圣地亚哥海岸齐腰深的海水处，圈养观察一些成年雌性豹鲨。这里的环境为这些豹鲨所喜爱。诺萨尔在豹鲨的背鳍出装上小型的无线电发射器。并利用占有凡士林的棉花堵塞了一半鲨鱼的鼻孔，通过这种方法来阻塞鲨鱼的嗅觉。

Nosal and his crew dropped the sharks about six miles away at a spot in the open ocean. The researchers then tracked the sharks as they tried to swim back home. Four hours later, the sharks that could smell were two-thirds of the way back home—and had swum in very straight paths. But the ones with stuffed noses took erratic¹² routes and only made it about half as far.

诺萨尔和同事们将这些鲨鱼放到六公里外的开放海域中。研究人员对这些鲨鱼进行跟踪记录，因为这些鲨鱼试图游回家。四小时后，嗅觉正常的鲨鱼距离家园只有1/3的路程，并且，它们游的路径是直的。但是，鼻子被堵塞的鲨鱼行程不稳，只游了约一半的距离。

Nosal thinks they all eventually got back home. “And we know that because even though their movements, even though they didn’t get as close to shore and even though their paths were more wind-y, their movements were still biased¹³ towards shore. On average they still finished closer to shore than when they started.” And those jelly-soaked cotton balls eventually disintegrate¹⁴, returning the sharks to normal. The experiment is the first to show that sharks can indeed sniff¹⁵ their way back home.

诺萨尔认为这些鲨鱼最终都能够回到家。“即使这些嗅觉受到限制的鲨鱼并未靠近海岸，同时它们的航线非常曲折，但他们仍在向海岸游行。总体而言，它们比开始时离海岸的位置近了。”这些棉花球最终会失效，鲨鱼的嗅觉就会恢复正常。此实验首次验证鲨鱼是靠嗅觉找到回家的路。

But it also shows that they must have some kind of back-up system that lets them that lets them navigate non-nasally. For Nosal, the next questions are: What’s the back-up system? And if sharks navigate by smell, what exactly is it they’re smelling that leads them—by the nose.

但是，此实验也表明，鲨鱼必须拥有一些在嗅觉失灵时进行导航的备用系统。诺萨尔的下一个问题是，那么这些备用系统是什么?如果鲨鱼利用嗅觉导航，它们利用鼻子到底在闻什么。