鲨鱼能听到近 250 英尺外的声音

Sharks are famous for their sense of smell, but new research shows that their hearing is impressive too. Scientists from Florida Atlantic University studied wild blacktip sharks in the clear, shallow waters off south-east Florida. They lowered an underwater speaker into the sea and played a series of low-pitched sounds. A drone hovering high above filmed how the sharks reacted, while special microphones measured exactly how loud the sounds were. The sharks responded to sounds coming from as far as 74 metres away – around 243 feet. That is a greater distance than had ever been recorded for free-swimming sharks. Often, they made a sharp turn away from the speaker, which suggests they could tell which direction the noise was coming from. They were most sensitive to the lowest sounds. When the researchers played a high-pitched sound that sharks are not thought to hear, the animals ignored it. Unlike most fish, sharks do not have a swim bladder, so the scientists believe they rely on their inner ears to pick up the movement of water caused by sound. The team also argues that testing sharks in tanks can give misleading results, because sound bounces off the walls. Studying them in the open ocean, they say, gives a much more natural picture.