There is concern that high intensity air-guns could have a deleterious effect on fish.  As demonstrated in a morphological study that we did in 2003, there is potential for damage to the sensory cells of the inner ear. More recently, we conducted a physiological study of the effects of air-guns on hearing in three species of fish. The work was conducted in   Inuvik, Northern Territories, Canada. We sought to determine if exposure of endemic fishes to a riverine seismic survey would impair hearing. The work was published as follows:

• Popper, A. N., Smith, M. E., Cott, P. A., Hanna, B. W., MacGillivray, A, O, Austin, M. E, Mann, D. A. (2005).  Effects of exposure to seismic airgun use on hearing of three fish species. J. Acoust. Soc. Am., 117:3958-3971.

The results of the study show that any effects on fish from exposure to repeated blasts of an air-gun are temporary, and recovered from, within 24 hours of exposure.  As in our LFA study, the signal level was probably well above the level that any individual fish would encounter. 

Experiments were done on three species, lake chub, broad whitefish, and northern pike, and there were differences in results for these species. We found some temporary hearing loss (Temporary Threshold Shift) in adult northern pike and in lake chub, but not in juvenile northern pike or broad whitefish. But, there was no apparent effect on the swim bladder of these fishes, and either no hearing loss or complete recovery in less than 24 hours of exposure.

We have also analyzed the structure of the ears of the fish exposed to seismic sounds and have found that there was no damage to any of the otolithic end organs when examined with scanning electron microscopy (Song et al., submitted).

Several important results come from this study:

1. This was the first study on any anthropogenic sound that examined changes in hearing sensitivity and in effects on the ear.
2. We found no damage to any non-auditory tissue -- though we recognize that unlike in our LFA study, we did not have access to a pathologist to examine histopothology.
3. There was rapid recovery for hearing loss, even when the loss was fairly large in the hearing specialist lake chub.
4. It is apparent that temporary loss of hearing can occur without damage to the sensory structures of the inner ear.

 In a companion study, we examined hearing in several additional species available to us in Inuvik.  These were published as:

• Mann, D. A., Cott, P. A., Hanna, B. W., and Popper, A. N. (2006). Hearing in eight species of northern Canadian freshwater fishes: implications for seismic surveys. J. Fish. Biol., 70:109-120.