[E329]Sharks Head Straight Home by Smell
Sharks Head Straight Home by Smell
Some sea creatures can find their way through thousands of miles of seemingly featureless[无特征的;无特色的] oceans. Even more impressive is the route that they take.
“Well, we’ve known for a long time that sharks are capable of[能够;有能力] long-distance migrations[移居,迁移;(鸟等的)迁徙,移栖;(鱼类的)回游], and in some cases those migrations occur along very straight paths[沿着直线].” Scripps Institution of Oceanography[斯克里普斯海洋研究所] biologist Andy Nosal. “And this has always begged the question[不禁提出一个问题]: how exactly do they know where they’re going?...So, there have been a lot of hypotheses[haɪ'pɒθɪsiːz][假定;臆测] floated over the last several decades, including the idea that these sharks are using, for example, geomagnetic cues[地磁信号], chemical cues[化学物质] and others. But none of these have really been systematically tested[系统验证/测试/检验] in the field.”
Nosal and his team suspected that the navigational secret of some sharks might be their sense of smell[嗅觉]. They use their keen[敏锐的,敏捷的] noses to find food, of course. And other fish, like salmon[鲑鱼;大马哈鱼], are known to use olfaction[ɑl'fækʃən][嗅觉]to navigate.
To see if his hunch[hʌntʃ][预感;大块;肉峰] was right, Nosal scooped up[用铲子取;兜接,舀上来] some adult female leopard sharks[豹纹鲨] in their preferred environment, waist-deep[齐腰深的] water off the San Diego coast[圣地亚哥海岸]. He attached a small radio transmitter[小型无线电发射器] behind their dorsal fins[背鳍]. And he blocked the sense of smell[嗅觉] in half of the sharks by shoving[推挤] cotton balls[棉球] soaked with[用…浸泡;使…充满] petroleum jelly[凡士林] in their nostrils['nɑstrəl][鼻孔].
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[鼻子被堵的] took erratic[不稳定的;古怪的] routes and only made it about half as far.
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[偏向] shore. On average they still finished closer to shore than when they started.” And those jelly-soaked cotton balls[浸泡(凡士林)的棉球] eventually disintegrate[瓦解;碎裂;衰变], 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]
But it also shows that they must have some kind of back-up system that lets them that lets them navigate non-nasally[没有鼻子地]. 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.
—Jason Goldman
From 60-Second Science
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