Physical effects of sound exposure from underwater explosions on Pacific mackerel (Scomber japonicus): Effects on the inner ear

Studies of the effects of sounds from underwater explosions on fishes have not included examination of potential effects on the ear. Caged Pacific mackerel (Scomber japonicus) located at seven distances (between approximately 35 and 800m) from a single detonation of 4.5kg of C4 explosives were exposed. After fish were recovered from the cages, the sensory epithelia of the saccular region of the inner ears were prepared and then examined microscopically. The number of hair cell (HC) ciliary bundles was counted at ten preselected 2500 mu m(2) regions. HCs were significantly reduced in fish exposed to the explosion as compared to the controls. The extent of these differences varied by saccular region, with damage greater in the rostral and caudal ends and minimal in the central region. The extent of effect also varied in animals at different distances from the explosion, with damage occurring in fish as far away as 400m. While extrapolation to other species and other conditions (e.g., depth, explosive size, and distance) must be performed with extreme caution, the effects of explosive sounds should be considered when environmental impacts are estimated for marine projects.

Automated summary

This study found that underwater explosion sounds have significant negative effects on the inner ear hair cells of Pacific mackerel, with the extent of damage varying with distance and location. Extrapolation to other species and conditions must be done cautiously, but the effects of explosive sounds should be considered in assessing environmental impacts of marine projects.