Killer whales can hear more than you thought

Washington, May 2: Marine mammals, including whales and dolphins, may hear more than previously thought as researchers have now discovered that these animals can hear sound emitted by commercial sonar systems, which are designed to create signals beyond the range of hearing of such animals.

Used for exploring and mapping the ocean, active sonar (short for sound navigation and ranging) devices emit pulse of sound into the water and if an object is in the path of the sound pulse, the sound bounces off the object and returns an "echo" to the sonar device.

How do the sonar signals actually sound to marine mammals?

Since high-frequency sonar pings several times per second, it is possible that it sounds like one continuous, high-pitched hum or ping, said the study.

Although the signals would not cause any actual tissue damage, they may affect the behaviour of some marine mammals, which rely heavily on sound to communicate, navigate, and find food.

"These sounds have the potential to affect animal behaviour, even though the main frequency is above what they primarily hear," said Brandon Southall of Southall Environmental Associates in the US.

For the study, researchers evaluated the signals from three commercially available sonar systems designed to transmit signals at 200 kilohertz.

The team found that while most of the energy is transmitted near the intended frequency of 200 kilohertz, some of the sound leaks out to lower frequencies within the hearing range of killer whales and other animals such as dolphins and beluga whales.

"These signals are quiet, but they are audible to the animals, and they would be relatively novel since marine mammals do not encounter many sounds in this range," Southall noted.

The study appeared in the journal PLOS ONE.