Shark Behavior - Searching for Food
Sharks have an extraordinary sense of long-range hearing. Their hearing is acute and enables them to detect sounds from hundreds of meters away. A shark can hear or detect vibrations in the water with its whole body. They are attracted to the rapid and irregular, low frequency sounds produced by struggling or injured fish.
In this experiment we wanted to test the hearing sense in reef sharks (Carcharhinus perezii). We used rattles under water to produce intermittent bursts of low-frequency sound to attract sharks. These worked like a dinner-bell and attracted sharks from a wide area within minutes.
We started our dive in an area where we did not see any sharks for the first hour. After that I shook the rattles for about 5 minutes. Suddenly the first shark showed up, rapidly displaying searching behavior. We stopped shaking the rattles. The shark continued to look for food, circled us 3 times, and left. We waited for 5 minutes, went into a hiding place behind a big rock, and start shaking the rattles again. This time three sharks showed up, well oriented to the sound source, but displayed more searching behavior looking for food. They found us in 2 minutes. We stopped the rattles as soon we saw the sharks. This time they came closer, more determined to find were the food was.
It was amazing how fast they responded, displaying the behavior associated with selective attention to the sound stimuli. Reef sharks perform a wide variety of behavioral activities in the vicinity of a source of sound. This provides an opportunity to repeatedly observe various patterns of movements. This behavior makes them dangerous to swimmers, especially if the swimmer splashes about a great deal and makes considerable noise.
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Postcards from the Field: Shark Watching