A potential explanation for marine mammal strandings

The stranding of whales following naval exercises has been a topic of increasing interest. A recent article [P. D. Jepson et al., ‘‘Gas‐bubble lesions in stranded cetaceans,’’ Nature (London) 425, 575–576 (2003)] has suggested that some version of decompression sickness may be involved. Considerable additional evidence has been presented that indicates both acute and chronic effects of these bubbles. We suggested some time ago [L. A. Crum and Y. Mao, ‘‘Acoustically enhanced bubble growth at low frequencies and its implications for human diver and marine mammal safety,’’ J. Acoust. Soc. Am. 99, 2898–2907 (1996)] that the acoustic fields produced by naval sonars could induce bubble formation under certain conditions, particularly if there were a high level of nitrogen supersaturation in these animals. Recent evidence of high supersaturation levels [D. S. Houser, R. Howard, and S. Ridgway, ‘‘Can diving‐induced tissue nitrogen supersaturation increase the chance of acoustically driven bubble growth in marine mammals?,’’ J. Theor. Biol. 213, 183–195 (2001)] has stimulated us to perform a series of experiments that suggests that even modest acoustic intensities can trigger bubble formation under supersaturated conditions. Once bubbles are nucleated, these local supersaturation levels then result in bubble growth to macroscopic sizes, and their potential deleterious bioeffects. The results of these preliminary experiments will be presented. [Work supported by APL IR&D funds.]