Loud Noise Can Injure Fish Hearing

In the first ever study of the effects of loud man-made, or anthropogenic, sound on fish in the wild, University of Maryland professor Arthur N. Popper and his colleagues found that the injury to fish ears, and thus hearing, was even greater than they had anticipated. Their study appears in the January issue of the "Journal of the Acoustical Society of America."

"Studies have shown that loud noise affects marine mammals' hearing, so we had every reason to think we would see effects in fish too," Popper says. "But we were surprised that the trauma was so extended and so great."

With ears similar to those of other vertebrates, including mammals, most fish use hearing to sense their acoustic environment. Many use sounds to detect predators, find prey and communicate to find mates. Loss of hearing can leave fish very vulnerable to predators or with a loss of ability to find mates.

In his years of studying fish hearing, Popper has seen that fish sensory hair cells -- the cells that enable hearing in all vertebrates -- repair themselves if damaged, something human sensory hair cells cannot do. But in this experiment in an Australian harbor, Popper and his colleagues found evidence that the fishes' hearing not only was badly damaged, but that the sensory hair cells didn't grow back, even over a two-month period.

Popper's research took place in Jervoise Bay in Western Australia. The fish were pink snapper, a commercially important species that runs about 12-14 inches in length.

The noisemaker was a seismic air-gun, a tool routinely used to search for underwater oil deposits. The air-gun sound is sent repeatedly through the water, where it travels to sub-sea rock strata and back up. Fish within hearing distance of the air-gun literally get an ear full.

The pink snapper were placed in a cage at varying distances from the air-gun and exposed to different levels and repetitions of sound from the air-gun.

"When we examined the ears of the fish, we found holes in the hearing part of the ear, in the regions where we expected to find sensory hair cells," Popper explained. "The hair cells had either been ripped away, or we found evidence that the cells were dying."

The researchers examined fish at different intervals after their exposure to the air-gun sounds. The last group, examined after 58 days, had the most advanced damage. "Normally fish continue to produce sensory hair cells for much of their lives," Popper said. "However, the damage in the ears of the pink snapper suggests that regeneration, even if it occurred over the 58 days, didn't counteract the loss of cells that resulted from the sonic damage."

Popper says that in a setting where fish are able to swim away from the sound, they may flee the source of the sound. "However, behavioral studies have shown that some fish exposed to air-gun signals display disoriented swimming behavior.

"There's no doubt that we need more studies to understand everything in this process," Popper said. "But our results suggest caution in using devices that make intense sounds in environments inhabited by fish and marine mammals. It's not unrealistic to say that loss or reduction in hearing of a species could lead to a reduction in the population."

Popper served on the National Research Committee on the Potential Impact of Ambient Noise in the Ocean on Marine Mammals, which is slated to release its report on Feb. 10. He also is co-director of the University of Maryland's Center for Comparative and Evolutionary Biology of Hearing and director of the university's Neuroscience and Cognitive Science program.

Popper's collaborators on this research were Robert D. McCauley and Jane Fewtrell, Curtin University, Perth, Western Australia.

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For more on Popper's fish research, visit: http://www.life.umd.edu/biology/popperlab/