In a recent study with Robert McCauley and Jane Fewtrell of Curtin University in Perth Australia ,we examined damage to the ears of fishes exposed to an operating air-gun that was moved towards and away from the animals. The damage was regionally severe and there was no evidence of repair or replacement of damaged sensory cells up to 58 days after exposure. This work was published in the following paper.
The following three figures provide an overview of the results.
Our results show that exposure to an air gun will cause statistically significant damage to the saccule of the ear of at least one species, the pink snapper (the other end organs were not examined). 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. Either damage continued to accrue well after insult, regeneration was slowed or ceased, or significant regeneration did not occur until beyond the 58-day sample period.
We are cautious to point out the caveats in considering the implications of these results.
(1) The fish studied were caged and could not swim away from the sound source.
(2) We only examined a single species and it is possible that pink snapper are more or less sensitive to intense stimulation than other species.
(3) The impact of exposure on ultimate survival of the fish is not clear. Fishes with impaired hearing or vestibular senses would have reduced fitness, potentially leaving them vulnerable to predators.
(4) Although the full exposure regime was accurately quantified, the approach-departure nature of trials meant a precise air-gun exposure required to produce the damage observed, was not obtained. Was it the few high level signals or the accumulation of many moderate to high level signals?
Our study shows for the first time that exposure of fish to seismic air guns can result in significant damage to the ears of fishes. Clearly, we need to undertake further studies to better understand the response to the intense sounds, the repair process (if any), the impact on behavior and fitness, and the kinds of exposures that lead to maximum (and minimum) damage to the fish.
Our results lead us to suggest that one must show caution in the application of very intense sounds in environments inhabited by fish.