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Fish audio sensory cells damaged by seismic airgun tests; lower image is a close-up of square area (Pic: University of Maryland) |
The intense high-energy sound made by seismic airguns used in underwater oil exploration damages the audio organs of fish, the first ever study of their impact on fish in the wild has found.
The degree of injury to fish hearing was even greater than expected, according to a joint American-Australian research team led by Professor Arthur Popper of the University of Maryland published in the current 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 said. "But we were surprised that the trauma was so extended and so great."
The team included marine biologist Dr Rob McCauley and Jane Fewtrell of Curtin University of Technology in Perth, Western Australia.
Because most fish use hearing to detect predators, find prey, communicate and find mates, a loss of hearing can have profound - perhaps even fatal - effects for them. Oil explorers routinely use seismic air-guns to send intense sound pulses through the water column to the sea floor, then analyse the returning echoes to help gather information about the underlying rock strata.
Popper points out that fish have an ability that humans don't have: the capacity to repair damage to the sensory hair cells that enable all vertebrate animals to hear.
But in experiments conducted in Jervoise Bay, in Western Australia, the team found evidence that the airgun sound not only badly damaged the sensory hair cells, but that the cells did not grow back even after two months.
"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 said. "The hair cells had either been ripped away, or we found evidence that the cells were dying."
The fish used in the experiments were pink snapper, a commercially important species. They were placed in cages in the bay at varying distances from an air-gun, and exposed to different levels and repetitions of sound from it.
The researchers microscopically examined the fishes' ears at different intervals after their exposure. Those examined after just 18 hours already had holes evident where the sensory cells had been lost. The last group, examined after 58 days, had the most advanced damage.
"While we know that fishes can regenerate hair cells in the ear, the damage in the ears of the pink snapper suggests that regeneration, even if it occurred over 58 days, did not counteract the loss of cells resulting from sonic insult," the team concluded.
Popper cautions that it is not known whether pink snapper are more - or less - sensitive than other species to intense sound, and that the fish studied were caged and could not swim away from the sound source.
"However, behavioural studies have shown that some fish exposed to air-gun signals display disoriented swimming behaviour," he said.
Bob Beale - ABC Science Online
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