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Fish Sense

When it comes to the scariest movie of all time, Jaws ranks near the top. The most terrifying scene is at the beginning when some unsuspecting vacationer paddles a few hundred feet from shore. As the camera follows the swimmer from below, you know something bad is about to happen. And sure enough, we hear the famous two-note Jaws theme and a massive, terrifying shape appears from the murk.

This classic Jaws moment raises a question: how was the shark always able to know when a victim was in the water? Was it able to see the body, or perhaps hear splashing near the water’s surface?

Sharks can of course see and hear, but the real answer is more exotic. All fish have an organ called the lateral line system. It stretches along the outside length of their bodies, consisting of many hair-like sensors that detect motion in surrounding water. This organ allows fish to sense movement even when they can’t see.

Since much of the motion in water is made up of currents, until recently it was unclear how fish distinguish between flowing water and moving prey or predators. German scientists at the University of Bonn may have found an answer.

According to their research, the lateral line system has two kinds of sensors: superficial ones on the skin’s surface, and ones within the skin. The superficial sensors respond to general currents and stream flow, while the ones in the skin detect sudden changes in the water’s speed–a sure sign of a predator approaching.

So the next time you find yourself in shark infested waters, here’s a word of advice: stay still.

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