Sound travels 4.5 times faster in water than in air and low frequency sounds (<100 Hz) can travel vast distances (>1000 km) with very little attenuation (NRC 2003). This transmission efficiency is likely why most marine animals, including whales and dolphins, are adapted to use sound the way terrestrial animals use vision: to navigate, detect prey, avoid predators, and to communicate. However, increasing industrialization means that the oceans are getting noisier. In the open waters of the North Pacific, anthropogenic noise has generally been increasing in intensity at a rate of approximately 3 dB/decade, largely due to increases in commercial shipping (Andrew 2002, McDonald 2006). Other noise sources include but are not limited to underwater explosions, seismic surveys, pile driving, sonars (both commercial and military) and underwater extraction industries. Consequentially, underwater noise has emerged as a conservation concern.

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