Below the waves, there’s a chorus of sound. Clicks, calls, whistles, songs, trills – sounds of all kinds. Many marine species, but notably cetaceans (whales, dolphins and porpoises), have evolved over millions of years to produce, transmit and receive an array of complex sounds to understand their environment, navigate, communicate, socialise, find prey and attract mates. This allows them to thrive in their underwater world where sound carries fast and far, much more so than in air, due to water’s high density. The distances that sound can travel in water can be vast, even across entire ocean basins.

Cetaceans are divided into two groups: toothed whales (Odontocetes) and baleen whales (Mysticetes). They use sound quite differently. Toothed whales use clicks for echolocation and various sounds for communication. Baleen whales, though, have developed one of the most sophisticated forms of communication in the animal world as far as we know: the whale song. A true evolutionary wonder, whale songs are enchanting, haunting and beautiful and can travel thousands of kilometres and last for hours, following complex melodic phrases and themes. Each population has their own song, but when populations are within earshot of one another, they often borrow phrases from the other population and add to and alter their songs.

Much about whale songs remains somewhat of a mystery to us, including how they create the sounds – believed to be through passing air between their organs – and why they sing. Both male and female whales make vocalisations, but only the male whales are known to sing, suggesting that it relates to mating. But of course, there could be other reasons, including, much like for us humans, pleasure and enjoyment and to be expressive.

The soundscape of the ocean is rapidly changing. In pre-industrial times, ocean soundscapes were bountiful with organic sounds – not just from whales but also fish and invertebrates. Marine animals would move and migrate throughout the ocean, interacting with their environments and one another with sound, having conversations across vast distances and singing to themselves and others. Today, the ocean is afflicted by a barrage of anthropogenic sounds from shipping, fishing, underwater construction, deep-sea mining, seismic surveys and the use of sonar. In addition to direct human-caused noise, there’s new noise from sea ice and storms due to climate change. Unsurprisingly, this cacophony is negatively impacting marine species: altering their behaviours; causing a stress response; impeding hearing or afflicting hearing loss; driving them away from their habitats and migratory routes; and disrupting their mating, breeding, feeding, nursing, socialising and communicating. Research has shown that whales reduce their singing in response to noise created 200 kilometres away.

The Anthropocene is defined by humans impacting and reshaping planetary systems; in a short time, we’ve rewired and dismantled living systems that are the product of aeons of evolutionary process. The ocean is no exception to this. But sound disruption to marine systems is only just entering public discourse despite marine species’ reliance on sound for all major life functions.

Many people are now calling for human-caused sound in the ocean to be considered similar to other environmental pollutants and for national and international policy to reflect this. Noise-causing activities should be reduced in or removed from critical habitats and migratory routes of marine species. With considered strategies and existing technologies, we can return the ocean soundscape to one that is healthy for its inhabitants.

It’s sad to think how drastically the soundscape of the ocean has changed during the lifetime of some whales still swimming in the ocean today, who may be over 100 years old. But now with scientific understanding and public and governmental support, they could swim and sing in less disrupted waters once again.

Sources upon request.