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.

Most marine life is actually quite robust and resilient – not surprising given the challenges of living in the dynamic and challenging ocean environments. But there are limits to the kinds of sounds that these animals can tolerate, both physically and in terms of interference with their communication and normal behaviour. Some of our initial concerns about direct harm, hearing loss, and mortality appear to be more limited than we might have initially feared. But other measured impacts such as sound ‘masking’ of important noises, such as disturbance of feeding, breeding and navigation, and physiological stress impacting immune function, are increasingly being revealed. These may be far more widespread than we originally appreciated.

I’ve spent the last three decades working on these issues with a wide range of marine mammals in the field, in the lab, within regulatory agencies and Congressional audiences, and more recently in efforts to inform and inspire the general public to care about them. I began as an academic researcher studying sound communication because I thought sea lion sounds were amazing. I was fortunate to work with one of the few research facilities in the world working on communication and noise impacts for marine mammals. We measured hearing and noise impacts on hearing using incredibly well-trained seals in some of the first-of-a-kind studies evaluating things like hearing loss and masking. We used those measurements together with recordings and observations of free-ranging animals to make predictions about communication ranges in natural settings and what would happen when we introduced noise pollution into the environment. These early research insights serve as the foundation of my career that has in some ways tracked the progress of the whole issue.

I came to Washington DC to run the ocean acoustics program for the US National Oceanic and Atmospheric Administration (NOAA) in the early 2000s. While NOAA had been faced with the issue of noise impacts for well over a decade at that point (in terms of how oil and gas seismic surveys might impact endangered whales in Alaska) the issue soon went in a different direction. Following a major whale stranding event in the Bahamas in 2000 and increasing evidence from other places that military sonar was causing mortal whale strandings, various navies and regulatory agencies, including NOAA, were presented with difficult questions and pressures about what was being done to prevent future strandings. These well-documented debates and struggles made their way from scientific meetings and public hearings to the courts to the U.S. Supreme Court. I had a chance, as a relatively young scientist fresh out of graduate school, to be immersed in the progression of this debate and in the scientific area surrounding it. From serving as an expert witness for the US government in that Supreme Court case to briefings on at the White House, I had a unique vantage on how the ocean noise pollution issue rose meteorically to the highest levels of government and regulatory attention.

Even while the sonar debate was raging, some of us working the science-policy interface on the ocean noise issue discovered that there was more to it than the public realised. Much more mundane noise sources such as the low-frequency rumbling of ships were adding vastly more noise globally than military sonar. And because they make these very low frequencies, their noise (like whale calls) can travel much further than active sonars and echosounder pings. NOAA initiated a series of meetings to increase awareness and technological approaches to reducing the noise from ships. Though a long and slow march, given the scale of the problem and complexity of the industry, we managed to bring this issue to the attention of the industry and ultimately to the United Nation’s International Maritime Organisation, who issued voluntary recommendations on the reduction of shipping noise to protect marine soundscapes.

In parallel with this broadening of the issue, much of the science inspired by questions around military sonar and seismic testing began to reveal the importance of sub-lethal effects on marine life and the ways in which noise could have cascading effects through ecosystems. Researchers began to focus on the interactions of stressors, cumulative effects, and how noise could increase stress hormones. The field began to ask more complex questions that revealed more complex aspects of responses. For instance, recent science has shown that what animals are doing at the time of disturbance can have massive implications for how they respond. Animals that are motivated and hunting are much less likely to leave an area than animals with less reason to remain – even if the noise exposure is similar or more intense. Animals are able to determine the range of a source and respond to things closer to them. Animal responses to noise interact with their consideration of other variables, such as the distribution of prey. These and other advances in our understanding are increasingly highlighting the importance of noise impacts on marine animals, but also the nuance required in addressing it.

We’ve also seen major strides in the international recognition of the issue within government and non-governmental organisations. New partnerships have formed to try and break down conventional barriers. There are now private-public efforts to monitor and reduce noise pollution from ships in several ports, notably the port of Vancouver. New certification programs for efficiency and noise pollution reduction provide incentives for reducing speed and noise, which has implications for both auditory impacts and vessel strikes.