Sharks Head Straight Home by Smell
鲨鱼可以闻到回家的路
Sharks that could smell headed straight back home when taken a few miles away whereas some that had their senses of smell blocked took slower, more erratic paths to their old haunts
鲨鱼离家几英里远的时候可以闻到直接回家的路，不过一些嗅觉失灵的鲨鱼会走更多弯路才能回去。

撰文：杰森·高盛
翻译：惠丹丹
审核：乔虹

Some sea creatures can find their way through thousands of miles of seemingly featureless oceans. Even more impressive is the route that they take.
一些海洋生物可以在看似毫无特征的海洋中跋涉千万里远找到回家的路。更让人吃惊的是它们回家所走的路线。

“Well, we’ve known for a long time that sharks are capable of long-distance migrations, 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 systematically tested in the field.”
“我们早就知道鲨鱼可以进行远距离的迁徙，而且有时是很长的直线迁徙。”斯克瑞普斯研究所的海洋生物学家安迪?诺萨尔（Andy Nosal）说，“这一点一直引起我们的争论：鲨鱼们到底是怎样知道它们要去哪里？.....因此，近几十年里有很多假设被提出来，包括鲨鱼用的是地磁线索或化学方式等想法。然而，这些假设没有一个被真正系统地验证过。”

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 salmon, are known to use olfaction to navigate.
诺萨尔和他的团队怀疑某些鲨鱼导航的秘密可能是在于它们的嗅觉。当然了，它们用敏锐的鼻子来寻找食物。其它鱼类如鲑鱼就是以嗅觉导航著称的。

To see if his hunch was right, Nosal scooped up some adult female leopard sharks in their preferred environment, waist-deep water off the San Diego coast. He attached a small radio transmitter behind their dorsal fins. And he blocked the sense of smell in half of the sharks by shoving cotton balls soaked with petroleum jelly in their nostrils.
为了验证他的猜想是否正确，诺萨尔把一些成年母猫鲨聚集到它们所喜欢的圣地亚哥海岸齐腰深的水域处。他在所有鲨鱼的背鳍绑上小型无线电发射机。并在一半鲨鱼的鼻孔里塞上用凡士林浸泡过的棉花球。

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 erratic routes and only made it about half as far.
诺萨尔和他的同事把这些鲨鱼放在六英里远处的开放海域中。然后研究人员追踪鲨鱼们回家的路线。四小时后，仍有嗅觉的鲨鱼已经走了2/3回家的路——而且走的直线路线。但是鼻子被塞住的鲨鱼却只走了一半的路程，而却走的是毫无规律的路线。

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 biased towards shore. On average they still finished closer to shore than when they started.” And those jelly-soaked cotton balls eventually disintegrate, returning the sharks to normal. The experiment is the first to show that sharks can indeed sniff their way back home. [Andrew P. Nosal et al, Olfaction Contributes to Pelagic Navigation in a Coastal Shark, in PLoS ONE]
诺萨尔认为鲨鱼们最终都会回到家里。“我们知道这是确定的，因为即使它们没有靠近海岸，即使它们的路线更加弯曲，它们依旧是向着海岸游去的。总的来说，它们都比刚开始往回游更加靠近海岸了。”那些凡士林泡过的棉花球最终也被分解不起作用了，被塞住鼻子的鲨鱼也回归了正常嗅觉。这一实验首次证实了鲨鱼们可以闻到回家的路。[Andrew P. Nosal et al, Olfaction Contributes to Pelagic Navigation in a Coastal Shark, in PLoS ONE]

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.
但实验也表明鲨鱼们肯定有其它备用手段来导航。对诺萨尔来说，下一个要解决的问题就是：它们的备用手段是什么？而且如果鲨鱼是通过闻味道来导航，那么到底是什么气味引领它们回家的。