Marine mammals live in environments where navigation is very difficult. They constantly have to find their way through their environment in the dark of night, the darkness of the deep ocean, ice covered waters, and the murky waters of rivers and coastal waterways. Marine mammals have demonstrated amazing abilities to navigate their way through even the harshest marine conditions. How are they able to accomplish such a feat? Many questions of how marine mammals navigate are still being investigated, but some answers have become clear. Sound plays an important role in navigation of marine mammals. Marine mammals also may use other cues for navigation. For example, in areas where marine mammals spend lots of time, they may use spatial memory to "map" their surroundings. Bats have a highly developed spatial memory that helps them travel through familiar locations; dolphins may use a similar technique.

The simplest manner in which marine mammals use sound to navigate is to listen to sounds in their environment. The sound of waves crashing on beaches conveys information about where coastlines are. This is important to large baleen whales (mysticetes) trying to navigate around small islands during migrations. In polar regions, where ice covers a large area of water, seals use sound to find holes in the ice. Ringed seals and Weddell seals listen for the sound of ice cracking and sounds being transmitted to the water from the air above ice holes to help find breathing hole locations. Blindfolded seals were able to locate breathing holes based on acoustic cues from up to 100 m away!

Weddell seals locate breathing holes by listening for cracking ice at the surface. Photo courtesy of Michael Van Woert, NOAA, NESDIS, ORA

Accurately detecting and localizing sound is also very important to marine mammals such as manatees and dolphins, which live close to the coast and encounter large number of boats. Being able to hear which direction boats are coming from provides these animals with information on the direction to swim to safely avoid them.

Some marine mammals also actively use sound to aid in navigation. The ability to use echolocation helps toothed whales detect and avoid objects that are too far away to see. Sperm whales and other deep diving toothed whales may also use echolocation to detect the sea floor in the darkness of the deep-sea. Baleen whales may also use low frequency sound to aid in navigation. It has been suggested that large whales may be able to orient or navigate in relation to features on the seafloor using returning echoes of their low frequency vocalizations. The low frequency sounds are different from high frequency echolocation clicks, but they may serve the same purpose in reference to navigation. It has also been suggested that bowhead whales can detect pack ice in polar regions by listening to the echo returns of their vocalizations.

References
• Ellison, W.T., Clark, C.W. and Bishop, G.C. 1987. Potential use of surface reverberation by bowhead whales, Balaena mysticetus, in under-ice navigation: Preliminary considerations. Report of the International Whaling Commission 37:329-332.
• Elsner, R. 1999. Living in water: solutions to physiological problems. Pages 73-116 in Reynolds, J.E. III and Rommel, S.A., (eds.). Biology of Marine Mammals. Smithsonian Institution Press, Washington D.C.
• Payne, R.S. and Webb, D. 1971. Orientation by means of long range acoustic signaling in baleen whales. Annals of the New York Academy of Science 188:110-141.
• Tyack, P.L. 1999. Communication and Cognition. Pages 287-323 in Reynolds, J.E. III and Rommel, S.A., (eds.). Biology of Marine Mammals. Smithsonian Institution Press, Washington D.C.
• Wartzok, D., Elsner, R., Stone, H,. Kelly, B.P. and Davis, R.W. 1992. Under-ice movements and the sensory bias of hole finding by ringed and Weddell seals. Canadian Journal of Zoology 70:1712-1722.