Sensitive Hearing

August 13, 2017
By Damond Benningfield
Episode:

450717-sensitive hearing.jpg

A sonar transmitter/receiver being lowered into the water from a helicopter. Credit: US Navy

To a whale, sonar can be the equivalent of a heavy metal concert. The sonar can overpower other sounds, so the whale can’t hear its companions or prey. If the sonar is especially close, it can cause hearing loss. And not to carry the metaphor too far, but the sound may lead to confusion that causes the whales to flee in terror -- and perhaps even strand themselves on the beach.

Sonar sends out pulses of sound, then records the “echo” from submarines, sunken ships, or even the ocean floor. And the sound can travel across hundreds of miles.

But whales and dolphins send out their own pulses of sound. They use the echoes to find mates, follow prey, and navigate. Anything that interferes with those sounds can cause problems.

And sonar appears to do just that. Studies have shown that loud sonar can cause whales to stop feeding and speed away from the sound. Biologists have seen bleeding in the ears and brains of whales subjected to loud sonar, and some whales have even developed the “bends” -- the affliction that can kill divers who rise too quickly.

Many whale strandings are also associated with sonar -- the whales swim up on the beach and die. Most of the strandings are by a rarely seen species known as Cuvier’s whale. But pilot whales, dolphins, and others have also been known to strand themselves.

A couple of years ago, the U.S. Navy agreed to limit sonar testing around Hawaii and southern California to protect the marine mammals there -- keeping their habitat a little quieter.