Marine Mammals and Ocean Noise

Abstract

Humans generate sounds in the ocean intentionally (e.g., sonar, seismic) and as a consequence of other activities (e.g., shipping). These sounds increase the noise level in the acoustic spectrum which one or more species of marine mammals utilize. Different marine mammal species are sensitive to sound at frequencies between 10Hz and 180kHz and thus all human-generated sounds have the potential to impact some marine mammals. Any sound that rises to the level of detectability has the potential to alter behavior. Louder sounds can interfere with acoustic communication or detection of relevant acoustic cues from the environment. Still louder sounds can lead to physiological changes such as temporary or permanent threshold shifts in hearing sensitivity with extremely loud sounds at very close range causing acoustic trauma. Continued exposure to noise causes stress reactions in humans and other terrestrial species and is likely to cause stress reactions in marine mammals. Determining the significance of any of these effects of human-generated sounds on marine mammal populations is exceedingly difficult, although exposure-response studies have resulted in some estimates of population impact.