Today’s Moment of Science is about the damage done to fish ears by very loud man-made sounds. I mean sounds like those of seismic air-guns, which are regularly used to search for underwater oil deposits.
The inner ears of fish are similar to those of other vertebrates, including mammals; what’s different is that fish don’t have a middle or outer ear. Fish use their hearing in order to detect predators, find prey, and to communicate in order to find mates. So a loss of hearing makes fish quite vulnerable.
In order to examine what damage may be done to fish hearing by loud, man-made noises, researchers placed pink snappers in cages at varying distances from a seismic air-gun so that they were exposed to various levels and repetitions of sound. When the fish were examined, researchers found holes where there should have been sensory hair cells. The hair cells were either ripped away or dying. Normally, sensory hair cells repair themselves when damaged, but even months later the fishes’ hearing had improved little if at all.
The sound of the seismic air-gun is sent repeatedly through the water, where it travels to sub-sea rock strata and back up. It could very well be, scientists say, that fish in the wild might swim away from the source of the sound, suffering less hearing damage than the pink snapper, who hadn’t a choice but to endure the sound repeatedly. However, studies have also shown that some fish exposed to the sound of a seismic air-gun display disoriented swimming behavior and may be unable to swim away.