Acoustics

Sound propagates effectively through seawater and many cetacean species (especially the odontocetes) have evolved a highly developed acoustic capability as a result of this. Sound is used for foraging, in reproductive behaviour and for general communication. Early work included the discovery that the “songs” of humpback whales could be heard over hundreds of kilometres during migrations to their breeding grounds. More recent studies have shown how dolphins and porpoises use series of high frequency “clicks” to search for and hunt down fish prey, and how dolphins use “whistles” to communicate with each other.

Because sound is the primary sense used by cetaceans, acoustic methods can be very effective in the study of cetacean ecology and behaviour. Acoustic surveys are increasingly being used to investigate the distribution and abundance of sperm whales, porpoises and dolphins. In these surveys, a hydrophone (underwater microphone) is towed behind a ship on the end of a long cable. The sounds heard are recorded on computers onboard the ship and used to calculate measures of relative abundance. Hydrophones attached to so-called sonobuoys moored in remote locations are used to record the low frequency sounds of baleen whales, and an acoustic recording device known as a POD (‘porpoise detector’) is a commonly used tool to monitor the use of coastal areas by porpoises and dolphins.

 


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