Ocean Noise

If you have ever had your head underwater while swimming in the ocean, you can probably appreciate how differently sound travels in water than in air; that motorboat you hear underwater is probably not directly on top of you. It only sounds that way. This is because sound travels roughly four to five times faster in water than in air depending on the water’s salinity, temperature and hydrostatic pressure. Sound also travels much farther in water. Even though Jacques Cousteau was a renowned explorer and filmmaker who introduced millions of viewers to the wonders of undersea life with his iconic 1970s TV show, he made several mistakes during the making of his early documentary The Silent World including the choice of its title. The ocean is anything but silent.

Human-generated sounds from the expanding marine economy since the Industrial Revolution have made the ocean noisier¹. As described below, it has now reached levels harmful to marine life, and it’s only getting worse. Ocean noise pollution became widely known to many people a decade ago through the release of Sonic Sea, an award-winning documentary by the Natural Resources Defense Council. I was invited to serve on a panel discussion following a local screening of the film. Seeing the expressions on the audience’s faces while they watched was amazing—the video is powerful. Yet many people today are unaware of the growing problem. I would recommend you stop reading this white paper and watch the documentary on YouTube at the link below², then return here for an update.

Background on Properties of Underwater Sounds

Sound can be thought of as vibrations moving through a gas, liquid or solid. When it moves through air, the gas molecules, having been excited by a vibrating object, are moving and bouncing and transferring energy to one another in a chain reaction. It is thus traveling as both the back-and-forth motion of particles and as a mechanical pressure wave. When located near the sound source, it is particle motion that is likely the primary acoustic stimulus for fishes and invertebrates; in some species it may be the only sound they can detect³. Many benthic invertebrates are also capable of sensing seabed vibration. When a pressure wave impinges on a solid structure like the cochlea of your ear, it is perceived as sound.

Sound waves can be described by their amplitude or intensity, frequency or pitch, and their wavelength. Sound waves with greater amplitude or higher intensity are perceived to be louder. Sound intensity level is measured in decibels (dB) which is a logarithm scale. The sound level of quiet conversations is roughly 50 dBs while the sound from a jet aircraft is roughly 120 dBs and exceeds a person’s pain threshold depending on their distance from the jet.

Frequency, or pitch, is the number of times per second that one wavelength repeats itself and is expressed as hertz (Hz). Most people are familiar with stereo settings for the bass sounds of drums and bass guitars that are low frequency waves (roughly 20 Hz to 500 Hz) versus the treble sounds from acoustic guitar strings, violins and flutes that are higher frequency waves (roughly 4,000 Hz to 20,000 Hz). When the radio’s equalizer is turned one way, the speakers are booming; turned the other way, they are piercing. Humans can hear a range in frequencies between 20 Hz and 20,000 Hz (or 20 kHz); whales can detect sound frequencies ranging from about 10 Hz to 200,000 Hz (or 200 kHz) with baleen whales thought to be the low frequency specialist at 10 Hz to 5 kHz and toothed whales and dolphins up at 200 Hz up to 150 kHz; fishes <50 Hz to 4 kHz³, and invertebrates 0.1 Hz to 25 kHz⁴. However, under laboratory conditions fishes respond to particle motions down to a frequency of 0.1 Hz, thereby showing that many fish are also sensitive to infrasound (i.e., < 20 Hz)⁵.

Sound waves lose energy and intensity as they travel away from their source as a function of the medium in which they are traveling. Water is denser and less compressible than air, meaning that although creating a wave takes more energy, the wave will travel faster once it begins than it would in air. Energy loss rate also depends on the wave’s frequency. High-frequency sound waves lose energy more quickly than low-frequency waves (due to heat loss from the more rapidly moving molecules). Loss over distance also depends on obstacles and reflections that can absorb, reflect or scatter the sound. As a result, sound travels faster and farther underwater than in air. Research by the Monterey Bay Aquarium Research Institute shows that their underwater microphone (hydrophone) can pick up sperm whale clicks from 160 km away (~100 mi)⁶. Combined, these properties make the ocean an acoustic environment.

Why Hearing is So Important to Marine Organisms

Think of a time when you were standing near the speakers at a rock concert or when you were in your car sitting at a light next to a car owned by some jerk blasting his subwoofers—you felt not just heard the low-frequency bass sound waves. Because their tissues are so similar to the surrounding medium, marine organisms can feel underwater sound through their bodies. Yet to capture and pinpoint the directionality of sound waves, sea creatures have evolved specialized sensory systems. Examples include the statolith and chordotonal organs of invertebrates; the otolith organs, lateral line system and gas-filled swimbladder of some fishes; and the macula neglecta in sharks; and the melon and highly specialized mandibular fat channels of whales and dolphins ⁴,⁷,⁸. Many marine organisms can also make various sounds. They rely on sounds produced by themselves or others to acoustically sense their surroundings, locate food, in territorial defense or to deter predators, initiate social interactions and to broadcast sexual readiness.

One of the earliest investigations into ocean sounds centered on determining the source of noise coming out of the hydrophone that sounded like frying fat or crackling bacon. A U.S. submarine operating in the Makassar Strait in 1942 reported the sound and suggested it was a “newfangled gadget dropped in by the Japanese”. The University of California, Division of War Research at the U.S. Navy Electronics Laboratory discovered the sound was being produced by thousands of tiny snapping shrimp closing their oversized claws at extreme speeds⁹; subsequently it’s been determined that it is actually the sound of cavitation from collapsing bubbles produced when the claw is closed¹⁰. The sonic blast of snapping shrimp is thought to stun prey and deter predators. The same sound has also been found to attract larval oysters looking for a reef on which to settle¹¹. Pelagic larvae of certain coastal fishes and crabs have also been found to orient towards sounds when seeking suitable settlement habitat⁴. Most people are probably more familiar with and frightened by the idea that sharks and other fishes are attracted to the thrashing sounds of injured or struggling animals in the water³. At least 800 species of fishes have been shown to produce various sounds, including grunts, croaks, clicks, and snaps⁷. One impressive example is the sound made by the oyster toadfish by rapidly vibrating specialized muscles against its swim bladder that reportedly sounds like a foghorn and serves as its mating call.

However, it may be the haunting sounds of whale songs that most people are familiar with. The public got their first taste of whale songs when an album of humpback vocalizations was released by Capitol Records in 1970 (open this link in another tab https://www.youtube.com/watch?v=AXCYrXdJpTA). The recordings were made by a U.S. Navy sonar engineer, Frank Watlington, while he was attempting to track submarines off Bermuda in the 1950s and 60s, and remastered by the bioacoustician Roger Payne. Sperm whales are reported to produce the loudest sound of any animal at 230 dB to 236 dB¹². It is a high-frequency click similar to that used by other toothed whales (e.g., orca, dolphins) and functions like the sonar systems on navy ships to find prey. However, it is the blue whale that produces the most powerful sustained vocalizations at 188 dB¹³. Vocalizations of blue whales consist of a combination of two low-frequency, long-duration sounds: pulsed A calls and tonal B calls¹⁴. Rhythmic, repeated sequences of A and B calls that have different pitches have been classified as songs¹⁵. Only males (of blue, fin and humpback whales) have been recorded producing A and B calls, i.e. singing¹⁴. Initially they were thought to be calling females; however, playback studies involving humpbacks consistently showed females did not approach the singer and instead males approached¹⁶. This led to a theory that songs were being directed at other males to form a lek¹⁶. A lek refers to a location where males assemble to exhibit, sing, or fight to demonstrate their genetic fitness to females. Whale songs can differ both diurnally and seasonally¹⁷. In Monterey Bay, whales sing during the evening and stay relatively quiet during the day, but this pattern reverses when the whales begin their migration. Blue whales—of both sexes—also produce short, low-frequency vocalizations termed D. These shorter calls are thought to maintain cohesion or attract individuals to patches of food. Sound clearly serves an essential function in multiple aspects of marine life.

Sources of Noise Pollution

Human activities, such as shipping, military and industrial activities (e.g. seismic surveying, resource extraction, aquaculture, fishing) generate sounds over a wide range of amplitudes and frequencies (10 Hz to 10 kHz) much of which overlaps with the low to mid frequencies utilized by marine animals. One of the most ubiquitous anthropogenic sounds is from large vessel traffic associated with commercial shipping (10–500 Hz). The world’s commercial fleet has roughly tripled over the past fifty years¹⁸. The sound from these large vessels and those from smaller vessels (like the one that seems to be right on top of you when swimming) are low-frequency continuous sounds from the propeller but can also include the much louder sound of cavitation, the violent collapse of bubbles just like those produced by snapping shrimp. Some of the loudest and most intense anthropogenic sounds in the marine environment are from impulsive sounds from industrial (e.g., pile driving, drilling, tunnel boring and airguns used in oil exploration) and military activities (e.g., explosives, sonar).

The U.S. navy has exploited the acoustic properties of the ocean for transmitting and monitoring sound as far back as World War II when the Sound Fixing and Ranging Channel (SOFAR) was discovered (e.g., SOFAR bombs used by downed pilots¹⁹ and as part of their Sound Surveillance System tracking submarines).

The SOFAR is a natural ocean “channel” for sound waves often located at a depth of a few hundred meters, where low-frequency sound waves can travel long distances by bending or refracting off the steep temperature gradient near the surface and the steep pressure gradient deeper down. An experiment in 1991 to assess if acoustic transmissions could measure ocean warming clearly demonstrated the speed and vast distances that sound can travel within the SOFAR channel. Using suspended acoustic sources lowered from a ship on loan from the U.S. Navy near Heard Island in the southern Indian Ocean, scientists transmitted low-frequency signals that were detected only hours later by receiving stations ranging up to 20,000 km (>12,000 mi) away²⁰.

Biological sounds can also travel great distances in the ocean depending on amplitude and frequency. A study using the U.S. Navy’s Sound Surveillance System reported that under the proper conditions, and using the correct filters, blue whale calls may be reliably detected from 400 km to 600 km (250 mi to 375 mi) away²¹. But as discussed above, due to its density and incompressibility, sound can travel great distances in the ocean even outside the SOFAR channel. The high-intensity, low-frequency calls of the Antarctic blue whale have been detected at distances of up to 200 km (124 mi)²². Airgun sounds were recorded in the North Atlantic almost continuously during the summer months, having originated at locations over 3,000 km (>1,800 mi) from the receiving hydrophones²³.

Adverse Effects of Noise on Marine Organisms

There are four general categories of noise impacts on marine life: physical injury, physiological effects, behavioral changes and masking. This update is not intended to summarize all the research conducted and will only mention a select few papers. The type of effect will depend on the sound pressure level at the source, the pitch (frequency), the distance between source and receiver, and the amount of background noise. The nature of the impact will also be determined by the characteristics of the impinged auditory system. Put simply, does the produced sound coincide with frequencies that marine organisms can hear? As stated above, the frequency of anthropogenic sounds generally overlap with the hearing and acoustic communication ranges of many animals²⁴,²⁵. However, in humans, noise has been found to have an adverse effect even at frequencies that cannot be heard. A group at MacEwan University reports that infrasound (frequencies below 20 Hz) can cause elevated cortisol levels, irritability and sadness in humans without being detected as sound²⁶. It is not unreasonable to assume the same for marine organisms.

Invertebrates, both adult and early-life stages, have been found to exhibit physical and behavioral effects from anthropogenic noise⁴. Larval stages of crustaceans, bivalves and gastropods have been found to delay hatching, have impaired development and higher mortality when exposed to anthropogenic noise⁴. High-amplitude noise, such as that from a seismic survey airgun, has also been found to cause mortality of marine zooplankton, including krill. These effects extended out to at least 1.2 km from the source, which was the maximum range monitored²⁷. Adults of many invertebrate taxa have been found to exhibit alarm behavior (startle responses), elevated stress hormone levels, higher oxygen consumption rates, and, in bivalves, increased rates of valve closures⁴. In an experiment using primacord detonation as a high-amplitude impulsive sound, blue crabs had up to 60% mortality depending on distance from the detonation center²⁸.

Pressure waves from distant sources can cause marine fish to change their behavior, resulting in impaired spawning, interference in foraging and feeding, or disruption in migrations and habitat selection²⁷. Catch rates of cod and herring were reduced out to 33 km (> 20 mi) due to the noise from seismic surveying; however, based on the hearing sensitivities of the fish some have suggested they would be able to perceive pile driving at distances, possibly up to 80 km (50 mi) away²⁷. They can also experience elevated stress hormone levels and temporary hearing loss⁷. Even non-lethal effects could cascade and result in changes in population structure.

Greater attention has been paid to the harmful effects of noise on marine mammals, and since ship noise peaks at low frequencies, initial research mainly concentrated on baleen whales. Due to the inherent difficulties in observing fast-moving, wide-ranging, and often submerged animals, most accounts of altered behavior in wild marine mammals emphasize physical behavioral changes visible at the surface instead of acoustic behavior. Of the whale species that have been studied (e.g., bowhead, humpback, fin) most move away from ship noise ⁸,²⁴. North Atlantic right whales seem to be the exception to the rule, however. They reportedly rarely flee from low-amplitude vessel noise. Researchers speculate that this may account for the higher number of vessel collisions involving these slow-moving whales⁸. However, it is not just ship noise that is of concern. Naval sonar has received a great deal of public attention in terms of its impacts on whales²⁹. Mass strandings of beaked whales have been associated with the operation of military mid-frequency active sonars³⁰. Some have speculated that swimming away from active sonars in shallow water may lead whales to become stranded or may cause them to ascend rapidly, which would produce decompression sickness³¹. Likewise, the impact that impulsive sounds of airguns used in seismic surveys have on whales has also received a great deal of attention³². After airgun activation, some whales have been observed suddenly diving or slapping their flukes on the ocean surface.

Gray, humpback, and fin whales not only move away from ship noise but also modify the pitch, duration, and rate of vocalizations—some vocalizations increase while others decrease—when exposed to elevated background noise from large vessels or airguns⁸. Humpback whales have been shown to increase the amplitude of their vocalizations with increasing background noise from ships, but vocalize less frequently⁸. In a controlled study using a passenger-cargo liner that was operated once per day distant from shipping lanes, humpback whales temporarily reduced singing or ceased singing altogether until after the ship passed to a minimum distance of 1,200 m³³. Studies of bowhead whales have found them to initially increase vocalization when exposed to airgun noise, but as the amplitude of the noise increased, individual call rates decreased⁸. Although North Atlantic right whales may not flee ship noise, they do exhibit a vocal response to it. At higher levels of noise, right whales vocalized less often but increased the rate of higher-frequency calls termed screams (400–3,200 Hz) that are mostly produced by females interacting at the surface⁸.

One way to assess the causal relationship between a stressor and its purported effect is to remove the stressor and see what happens. After the attacks on September 11, 2001, ship traffic in the Bay of Fundy decreased, leading to a 6 dB drop in background noise, particularly below 150 Hz. During this same period a study monitoring stress-related hormones in North Atlantic right whales in the bay found levels decreased³⁴. During the COVID-19 lockdown when there were fewer boats in Caño Island Biological Reserve in Costa Rica, diurnal patterns of humpback singing activity changed as compared to before and after the lockdown; singing increased during the day when fewer boats were on the water³⁵. Similarly, a shift in the type of boat activity during COVID-19 lockdown in Dolphin Bay, Bocas del Toro, Panama resulted in lower ambient noise levels and more frequent detections of dolphin sounds during the day that included a more diverse whistle repertoire than in the pre-lockdown period³⁶.

Obviously, it is difficult to determine whether the whales’ response in these studies was due to noise (or its absence) or to the presence of the boats (or their absence). The majority of these studies examined animals’ responses to real vessels in situ, with only a few using playback of pre-recorded sounds. Many have argued for more controlled experiments using playbacks³⁷. However, the limited studies that have employed playbacks generally find similar reactions to those described above. For example, playback of mid-frequency sounds simulating sonar has been shown to significantly affect blue whale behavior, especially during deep feeding modes³⁸. Gray whales exposed to playback sounds (of large tourist vessels and fishing skiff noises recorded elsewhere) varied their calling behavior depending on source, duration, and presentation of the sound³⁹. Resting mother-calf humpback pairs exposed to high noise playbacks of a 4-stroke Yamaha 100 hp outboard engine (simulating a whale watching boat) spent less time resting, increased their respiration rates two-fold, and swam faster compared to control and low noise treatments⁴⁰.

Naturally, some studies found animals exhibited minimal or no response to noise (or its removal). As cautioned by several of the authors referenced here, it is important to understand the outcome of animal behavior studies are often mixed or conflicting because an animal’s reaction is likely influenced by the type of activity it is involved in at the time of exposure (e.g., foraging, travelling with a calf, or resting), the habitat it occupies, the ambient noise levels (both natural and human-made), and prior exposure, including habituation or sensitization. Nevertheless, the evidence is generally considered sufficient to show that marine organisms can experience harmful effects from human-generated noise (see reviews referenced here).

Deep-Sea Mining (DSM)

Ocean noise pollution is only going to escalate with seafloor mining. Commercial shallow seafloor mining has been authorized by various nations within their exclusive economic zones, such as the Republic of Nauru, Papua New Guinea, Namibia, and South Africa, among others. There is growing momentum internationally and within the U.S. to commence deep-sea mining (DSM), particularly for polymetallic nodules from the Clarion-Clipperton Zone (CCZ) located 800 km (500 mi) southeast of Hawaii, as well as metal-rich massive sulfide deposits within the Semenov cluster along the Mid-Atlantic Ridge. These regions that are areas beyond national jurisdiction (ABNJ), fall under the regulation of the International Seabed Authority (ISA), a UN agency. The ISA has already granted 31 exploration contracts for DSM, including 17 within the CCZ, and was anticipated to publish the “Mining Code” (with regulations) in July 2026 that would have enabled mining to commence, but did not meet the deadline. The U.S., however, never ratified the 1982 United Nations Convention on the Law of the Sea (UNCLOS) that granted authority to the ISA. On April 24, 2025, Executive Order 14285 instructing federal agencies to fast-track the evaluation and granting of seabed mineral exploration licenses was signed by Trump. The National Oceanic and Atmospheric Administration (NOAA) is expected to grant a final exploration license to The Metals Company USA by October 2026, also within the CCZ. Considering the present interest and possible economic benefits, DSM is likely to expand quickly.

DSM will involve surface vessels acting as “mother ships,” overseeing networks of vehicles working above the seabed, remotely operated vehicles on the seabed thousands of meters below, a series of riser pumps for lifting the slurry up to the surface, all operating 24 hours a day. This is expected to generate continuous noise pollution across multiple depth zones, possibly becoming entrained and channeled within the SOFAR. In addition, mined materials will be transported by ships to processing plants on land, or potentially, ships might process the materials at sea to circumvent environmental regulations on waste disposal onshore. 

Noise from mining activities is expected to result in both near-field and far-field effects similar to those described above. A model estimating noise from nodule mining equipment predicted that noise from a single operation will surpass ambient levels in calm weather up to about 500 km (~310 mi) away but would exceed NOAA’s 120 dB threshold for potential behavioral effects on marine mammals up to 6 km away⁴¹. Imagine the combined noise produced by numerous operators mining around the clock. The continuous low-frequency sounds produced by ships and mining equipment could interfere with the communication and feeding behaviors of resident and migrating whales, possibly resulting in the abandonment of feeding grounds and migration routes. Impulsive sounds may trigger startle reactions and rapid ascents or cause whales to lose contact with offspring. Invertebrates and fishes are likely to detect substrate vibration or the particle motion aspect of sound up to more than 1 km away⁴². Unlike marine mammals, these animals cannot escape quickly from these disturbances.

It’s important to remember that sound usage is even more crucial to organisms living at this depth due to the constant darkness within the aphotic zone. Additionally, keep in mind this environment will have low background noise prior to the mining activities. Any effect at the population level would be particularly important because animals living at this depth grow slowly, reproduce at low rates, and therefore have limited resilience⁴².

While there is growing momentum to impose a moratorium on DSM⁴³, universal participation seems unlikely—particularly for U.S. firms—given the current administration’s forceful unilateral actions. Even if the moratorium is established, it seems inevitable that DSM will happen, eventually. For that reason, we should be working on developing strategies and technologies now that would lessen its environmental footprint⁴²,^44-46. The ISA has drafted a mitigation hierarchy that would include avoidance, minimization, restoration or rehabilitation, and offset⁴⁷. Some have expressed skepticism as to whether these actions will be successful in achieving the declared goal of no net loss of biodiversity⁴⁸,⁴⁹. Given the potential for far-field impacts from noise pollution, strategies will need to prioritize avoidance and minimization. The draft ISA mitigation hierarchy references established techniques for reducing noise from current activities, e.g., commercial shipping and piling driving, but acknowledges these measures are untested in deep water, and the sensitivities of the species therein are virtually unknown. Accordingly, significant investments should be made in advancing quieting technology, such as state-of-the-art propellers⁵⁰, and ensuring these technologies are incorporated into equipment before DSM operations begin⁴⁵. This effort should extend to quieting the sound from grinding hard surfaces and rattling of ores and slurry within riser pumps and pipes. It will be essential to restrict noise-producing actions close to the SOFAR channel⁵¹. Emphasis has also been placed on the necessity of researching the sensory ecology and behavior of deep-sea fishes and aquatic invertebrates⁴². The results of those studies should facilitate the establishment of noise exposure limits and acoustic impact thresholds tailored to different species. Results might also advocate for designating mitigation windows where noise-generating actions would be controlled or limited during peak animal density times, like migrations or breeding seasons. An onsite acoustic monitoring network that is standardized and calibrated will be essential for adaptive management⁵². Incorporating an adaptive management design should not, however, rule out adopting a precautionary approach at the outset. Finally, transparency from representatives of industry, government agencies, and the participating scientists will be crucial for continuous re-assessment of implemented measures’ effectiveness and to direct possible adjustments in management⁴¹,⁴⁶,⁴⁹.

Because these areas are so remote that public oversight is all but impossible, we must either trust that industry and governments will behave ethically or be prepared to finance watchdog non-governmental organizations. We must also hope that U.S. companies granted unilateral licenses by U.S. agencies under Executive Order 14285 will cooperate with mining interests awarded contracts by the ISA, and this does not turn into a geopolitical flash point. It seems that some designated areas are already overlapping⁵³. If conflict arises, and there is a rush to exploit the seafloor (akin to a new gold rush), the environment will surely be the biggest loser.

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