Energy and the Environment-A Coastal Perspective

When interpreting the effects of sound on underwater species, it is important to account for the frequency range differences that marine organisms are sensitive to. Fish, for example, are lower frequency hearers than marine mammals. The only metric for converting a spectral audio graph into a decibel measurement that denotes species-specific noise level is the dB_ht (Species) metric described in Nedwell et al 2007. This metric is useful for understanding the effects of loud sounds on organisms because it translates any sound spectrum into a level humans can identify with.

Both humans and other organisms avoid loud sounds because extended exposure can cause permanent hearing damage. The following sound levels cause behavior altering effects.

This species-sensitive metric has its weaknesses. Though loudness is one acoustic effect that could affect the behavior of a marine animal, these organisms also flee when exposed to sounds they perceive as a threat, regardless of the sound level. Though anthropogenic sounds rarely simulate the sounds of a predator, incidental biomimicry does occur. For example, some fish are thought to flee from high frequency sonar because they perceive the sound to be dolphin echolocation clicks. In these cases, an organism’s behavior could be affected at a sound level below the 75 dB_ht, the threshold for sound avoidance due to loudness.

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