How Underwater Noise Affects Whales and Marine Mammals

Put your head underwater on a busy morning in a harbour and listen. Long before you see a boat, you hear it: a low hum, then a whine, then a churning that seems to come from everywhere at once. Now imagine your whole life depends on hearing. That, in short, is how underwater noise affects whales and other marine mammals. Human sound can mask their calls and echolocation, trigger stress and changed behaviour, push them away from places they need, and, from the loudest sources, sometimes cause physical harm.

Sound behaves differently underwater

Sound and light do not travel the same way in water as in air, and that one fact shapes almost everything about how whales experience the ocean. Sound moves several times faster in seawater than in air, and it carries much further. That is why a ship you cannot see can still be loud.

Underwater, visibility is often poor. It is limited by depth, by particles, or simply by the lack of light below a certain point. So many marine species rely on sound the way we rely on sight. For whales, dolphins and other marine mammals, hearing is not a backup sense. Often it is the main one.

Why whales and dolphins depend on sound

Toothed whales, such as dolphins, orcas and sperm whales, use echolocation. They send out clicks and read the returning echoes to build a picture of what is around them, even in complete darkness. It is a remarkable natural sonar, used to find prey and to navigate.

Baleen whales, like humpbacks and blue whales, do not echolocate. Instead they make long, low-frequency calls that can travel great distances, probably to stay in contact with each other and, in some species, as part of mating behaviour. Both groups need a reasonably quiet ocean to do this well.

How does underwater noise affect whales? Three main ways

Research points to a few separate effects, not one general "noise hurts whales" effect.

Masking. When background noise overlaps the frequencies a whale or dolphin uses, it becomes harder for the animal to hear others of its kind, its prey, or the echoes of its own clicks. A 2019 study on Ganges river dolphins, an endangered and functionally blind species that finds its way by echolocation, combined field recordings with modelling. It found that boat noise heavily masked their clicks, changed how they vocalised, and at least doubled their estimated metabolic stress. Shallow water in the dry season made the effects worse (Dey and colleagues, Scientific Reports).

Stress and changed behaviour. Noise can trigger stress responses and interrupt feeding, breeding and communication. A well-documented example comes from Blainville's beaked whales in the Bahamas exposed to mid-frequency active naval sonar. Researchers estimated a 50 percent probability that foraging dives would be disrupted at a received level of about 150 decibels (Moretti and colleagues, PLOS ONE, 2014; a later correction gives 149.5 dB for the fitted curve). Closer to whale watching, Sprogis and colleagues approached 42 humpback mother and calf pairs in Exmouth Gulf, Western Australia, in 2020, with a boat playing back different levels of engine noise. At the loudest level, the mothers' resting time fell by about 30 percent and their breathing rate roughly doubled.

Displacement, and, rarely, physical injury. Constant or very loud noise can push animals away from the places where they prefer to feed or breed. At the extreme end, sound sources that are loud enough and close enough, especially certain military sonar exercises, have been linked to serious harm. After a 2002 mass stranding of beaked whales in the Canary Islands following naval exercises, Fernández and colleagues (Veterinary Pathology, 2005) described a "gas and fat embolic syndrome" in the animals' tissues and proposed a possible link with the sonar. This kind of sudden physical harm is documented but uncommon. Masking and changed behaviour are by far the more common, everyday effects of ocean noise.

Where does the noise come from?

The ocean has always had natural sounds: waves, rain, earthquakes, and the calls of marine life itself. What has changed is the human part. NOAA's Ocean Noise Strategy Roadmap (2016) names commercial shipping, naval sonar and seismic airgun surveys for oil and gas among the main human sources, together with activities like pile-driving for offshore construction.

Large ships are a particular worry. They produce constant, low-frequency engine and propeller noise, in the range many baleen whales use to communicate, and there are so many of them on more or less permanent routes around the world. One of the Roadmap's case studies looks specifically at chronic noise from commercial ships in large whale habitat.

Not every species is affected the same way

Hearing varies a lot between species, shaped by their biology and how they use sound. Baleen whales are generally most sensitive to low frequencies, which overlap heavily with ship noise. Toothed whales and dolphins rely more on mid- and high-frequency clicks for echolocation, which puts them at risk from different sources, including some types of sonar. This is one reason scientists study noise effects species by species, instead of assuming one effect for all.

What is being done, and what travellers can do

NOAA's Ocean Noise Strategy is a ten-year plan built on science, management, better assessment tools and public outreach. It moves attention from single loud events towards monitoring and predicting the whole soundscape, including everyday boat traffic. It is a serious, evidence-based effort: not a fix, but a real one. Critics have argued that it should also keep strong protections for specific loud sources, so it is worth following how it is applied.

For travellers, the lesson is simple. A quieter, slower boat is kinder to whales, even at the same legal distance. It is part of why, on our own trips, we treat sound the same way we treat distance: no chasing, slow approaches, and boats that hold back instead of crowding an animal that is clearly moving on. We rely on the judgement of our local experts, who know a bay's currents and wildlife patterns far better than any visitor. Our pages on how tourism boats can stress whales and on why mother whales are sensitive to boats look at the same research from the boat's point of view.

Wildlife encounters are unpredictable. Whale watching should always follow local regulations and experienced professional guidance.

On a boat day, the most useful gear is the kind that lets you stay back and still enjoy the moment. An underwater or action camera lets you film from the surface without moving closer, and a roll-top dry bag keeps it dry between sightings.

In short

Sound is not a minor sense for whales and dolphins. For many species, it is closer to the way we rely on sight. Human noise interferes with it in specific, well-studied ways: it masks signals, triggers stress and changed behaviour, pushes animals away, and sometimes, from the loudest sources like military sonar, causes real physical harm. None of this is a reason for alarm dressed up as certainty. It is a reason to keep following the research, and to think about the noise we personally add to the water. If this made you curious about meeting the ocean in a quieter way, you can explore our upcoming retreats.

Questions people ask

How does underwater noise affect whales?

Mainly by masking their calls and echolocation, and by causing stress and changes in behaviour such as interrupted feeding. Physical injury is documented but rare, and linked to very loud sources such as naval sonar.

What are the main human sources of ocean noise?

NOAA's Ocean Noise Strategy Roadmap names commercial shipping, naval sonar and seismic airgun surveys among the main sources, along with construction such as pile-driving.

Can sonar kill whales?

Beaked whales that stranded in the Canary Islands after naval exercises in 2002 showed gas and fat emboli, and researchers proposed a possible link with sonar. Such cases are uncommon, but they are taken seriously.

Does whale-watching boat noise matter?

Yes. A 2020 study off Western Australia found that humpback mothers and calves reacted more strongly to louder boat approaches, even when the approach itself was the same.

Do all marine mammals respond to noise the same way?

No. Baleen whales are most sensitive to low frequencies like ship noise, while toothed whales and dolphins rely on higher-frequency clicks and are affected by different sources.

Wildlife encounters are never guaranteed and never forced. Ocean Calling works only with vetted, ethical local operators, and every animal is free to approach, or not, entirely on its own terms.

Sources & further reading

1. NOAA. Ocean Noise Strategy Roadmap, 2016.
2. NOAA CetSound. Ocean Noise Strategy Roadmap overview.
3. Dey, Krishnaswamy, Morisaka & Kelkar. Interacting effects of vessel noise and shallow river depth elevate metabolic stress in Ganges river dolphins. Scientific Reports 9: 15426, 2019.
4. Moretti et al. A risk function for behavioral disruption of Blainville's beaked whales (Mesoplodon densirostris) from mid-frequency active sonar. PLOS ONE, 2014.
5. PLOS ONE, 2014. Correction to Moretti et al. risk function for Blainville's beaked whales.
6. Fernández et al. "Gas and fat embolic syndrome" involving a mass stranding of beaked whales exposed to anthropogenic sonar signals. Veterinary Pathology 42: 446-457, 2005.
7. Sprogis, Videsen & Madsen. Vessel noise levels drive behavioural responses of humpback whales with implications for whale-watching. eLife 9: e56760, 2020.

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