Sonar heard under water

Listening stations on the seabed all over the world are streaming sound in real time to websites that anyone can access, allowing people to hear everything from male humpback whales singing off Hawaii, to last year's Japanese earthquake.

Conscious of security, the US Navy has brokered a deal with scientists in the north Pacific which allows the navy to delete any sounds of US or Canadian military shipping before the audio is sent out across the internet.

It now wants to do similar deals with other scientists around the world, but some experts say that is both improbable, and in this new age of internet accessibility, unreasonable.

This is the sound of a sonar system in operation, best known for being used by submarines to determine the position, nature and speed of objects under the water.