How loud is loud?
The New Scientist raises an interesting question in its 11th November edition. The article notes that 'Sounds thought to cause only temporary hearing loss have destroyed nerve cells in the ears of mice.' It would appear that '... noises that aren't loud enough to affect hearing thresholds can still cause permanent damage to ear cells.'
The article goes onto note that when mice were exposed to a 100-decibel noise source, roughly equivalent to a motorcycle engine, several tests indicated that this noise level caused no long-lasting changes in hearing threshold. 'Under the gaze of a microscope, however, damage was seen to the part of hair cells that transmits sound via chemical interactions with nearby nerves. A year later, the damage had seemingly spread to nerves that
transmit sound to the brain (Journal of Neuroscience, DOI: 10.1523/jneurosci.2845-09.2009).
But what is the importance of this study for cetacean research? It would appear that a lot of research on ocean noise appears to concentrate on minimizing loud underwater noises to estimated thresholds. But what is really happening to whales and dolphins exposed to such noise? We may not be able to make such a leap from specially bred mice that have similar hearing characteristics as humans as used in this study to extrapolate to cetaceans, but lets also not dismiss our questions simply because we are talking of mice and men.
If long term damage is being caused to cetaceans are we yet to see long term conservation impacts? For such creatures that rely on sound to communicate, feed and generally 'exist' in a world of sound we may be storing up problems for the future.
WDCS has always called for a precautionary approach when it comes to noise pollution, yet we are often told mitigation methods employed by the extractive industries and the world's navies are 'appropriate'. Well it may be that there is not always an immediately evident impact, but this study may make us wonder what legacy we are leaving in our oceans.
There is a new feature film on Noise pollution just launching in Germany
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