It isn’t some ‘silent world’ as some have envisaged it. Rather, from the crashing waves and rumbling earthquakes to the incessant snapping shrimp and calls of whales, the underwater ‘soundscape’ is as vivid and dynamic as any rainforest or alpine meadow.

These sounds can provide answers to questions about the marine environment such as depth, bottom type, and the power of wind and waves. They can unveil features of oceanography, like thermal structure and even ocean acidity. So too can they tell us much about animals that live both near and far – some individual whales can be detected many hundreds of miles away by people and presumably by one another. We can use this underwater soundscape to unlock migration patterns and breeding behaviour of species rarely seen and little known, if we listen in the right ways and places for long enough. In the past half-century, humans have made major advances in listening to our underwater world in order to better understand and use it.

People have converged upon some of the same physical realities and solutions to operating and communicating in the ocean realm that marine animals have been evolving to deal with for tens and even hundreds of millions of years. Namely, sound is the most effective means of transferring information underwater because of how quickly light dissipates and chemicals mix. Marine animals preferentially use the acoustic channel, thus the vividness of the biological players in the ocean soundscape. Humans use it as well, through active imaging of sonar systems and sub-surface seismic visualisations. We also add our own noise pollution through the rumbling of massive ships, ocean industry and offshore construction.

We stand at a crossroads in understanding and managing our ocean soundscapes. We can see clearly how important the use of natural sounds are in key biological functions for many different species. From whales and seals to turtles, fish, and many invertebrates, ocean animals use sound for critical aspects of living. Our listening technologies are helping us measure and monitor populations. But we’re also now measuring and beginning to appreciate the expanding scale of our own noise pollution of the oceans.