How do fish hear?

In the ocean it's rare to see more than 100 metres, but distinct sounds can be heard for many kilometres.

Scientists now know that as man-made noise travels, it drowns out the natural ocean soundscape and makes it difficult for fish to hear each other.

This affects their ability to find food and mates, causes them stress and changes their behaviour.

"The sound level under the ocean has gone up, so rather than being in the quiet countryside, it's now like being in a city," said scientist Dr Steve Simpson.

In areas busy with boats and ships, scientists have even found physical damage in large mammals, like whales.

Watch scientist Dr Steve Simpson explain what fish 'ears' are like and how different fish hear.