The mysterious cry of the fin whale

There is a curious sound in the sea - almost a pure tone with a very low frequency of just 20 Hz. equal to the lowest recorded note sung by a human being. The song is heard in pulse sequences that last about 15 minutes, with 2.5 minutes' silence between. For years the sound was a mystery, until it was discovered that the '20 Hz. signal', as it became known, is produced by the fin whale.

With a body length of up to 85 ft. (26 m), the fin whale is second in size only to the blue whale, and is the fastest of the baleen (filter feeding) whales. Fin whales are gregarious creatures and their long distance calls, audible 500 miles (800 km) away, are thought to be the means by which relations and acquaintances keep in touch with on another.