Education hub //
Section 3. Sources and impacts of underwater noise
How do vessels produce noise?
Ships generate underwater noise – known as Underwater Radiated Noise (URN) – that spans a broad range of frequencies, from roughly 2Hz to 100kHz (OSPAR Commission, 2009). This noise includes:
- Tone-like sounds at specific frequencies (often associated with propeller rotation and machinery)
- Broadband noise spread across a wide frequency range (often produced by cavitation, turbulent flow, and vibrations from onboard machinery)
Together, these sounds contribute to the background noise that now dominates many coastal and offshore environments.
Main sources of ship noise
1. Propellers (cavitation)
When a ship’s propeller rotates rapidly, areas of low pressure form on the back of its blades, causing thousands of tiny bubbles of water vapour to form and then collapse – a process known as cavitation (Hildebrand et al., 2009).
When the bubbles implode, they generate a loud noise. Cavitation is often the dominant source of underwater noise from powered vessels and can account for up to 80-85% of total radiated noise from large commercial ships (Ross D. 1976).
2. Machinery
Engines, pumps, generators and other onboard machinery create vibrations that are transmitted through the ship’s hull and radiated into the surrounding water (Smith et al., 2022).
This type of noise is often:
- more continuous,
- concentrated at lower frequencies, and
- strongly influenced by ship design and maintenance.
3. Flow noise
As a vessel moves through the water, water flowing over the hull and appendages (like rudders, keels, and stabilizer fins) creates turbulence that generates noise.
Flow noise:
- increases at higher speeds, and
- can be amplified when turbulent flow from one structure interacts with another.
Why some vessels are noisier than others
Noise levels vary widely among vessels and depend on several key factors:
- Vessel type (e.g., cargo ship, ferry, fishing vessel, recreational boat)
- Ship design, including propeller type and hull shape
- Ship speed (noise often increases with speed)
- Maintenance of the hull and propeller
These factors mean that noise reduction is possible through improved design, maintenance, and operational choices – an important point for management and policy.
Boat noise source
Major human sources of underwater noise
Commercial shipping: the dominant noise source
Large commercial vessels generate predominantly low-frequency noise (typically 10-1000 Hz) that travels long distances underwater. These frequencies overlap directly with the communication frequencies used by baleen whales, including endangered species such as North Pacific right whales and blue whales that frequent British Columbia waters (Richardson et al., 1995).
At close range (within a few kilometers), noise from large ships can also mask higher frequency sounds, affecting species such as killer whales and other odontocetes that rely on sound to find food, navigate and communicate (Veirs et al., 2016)
Passenger vessels
Ferries and cruise ships create consistent and predictable noise patterns as they travel fixed routes multiple times daily. Although often quieter than large cargo ships, their frequent schedules and proximity to shore can result in chronic acoustic disturbance in near-shore habitats critical to marine mammals, fish, and many other marine organisms.
Recreational boating
Individual recreational boats may be quieter than large ships, but their cumulative impact can be substantial –especially in ecologically sensitive coastal habitats.
Industrial activities and marine construction
Industrial and coastal development are major contributors to underwater noise pollution. Key industrial noise sources include:
- Pile driving and marine construction. Major port expansions, bridge construction, and waterfront development projects generate some of the loudest underwater sounds, with pile driving producing intense, impulsive noise that can be heard over long distances.
- Dredging operations. Ongoing maintenance dredging creates continuous broadband noise over extended periods.
- Aquaculture facilities. Localized noise from increased vessel traffic, feeding systems, and maintenance activities
- Offshore energy exploration. Seismic surveys for oil and gas exploration generates extremely loud sounds that can affect marine life across vast areas.
Military and government activities
Naval exercises and training activities also contribute to underwater noise, particularly through the use of sonar systems, which can produce powerful sounds that propagate over long distances.
Why this matters
Together, these sources have transformed many marine environments from places dominated by natural sounds into soundscapes shaped largely by human activity. Understanding where underwater noise comes from is a critical first step toward reducing its impacts on marine life.
Hearing ranges of marine species
Sound production and hearing ranges vary widely among marine species. In general, animals tend to produce sounds within the frequency ranges where their hearing is most sensitive.
Estimating hearing ranges in marine species can be challenging. Researchers rely on a combination of behavioural tests, physiological measurements, anatomical studies, and predictive modelling to estimate what are often referred to as functional hearing ranges – the frequencies an animal is likely able to hear and use in real-world conditions (Southall et al. 2019)
Baleen whales (mysticetes)
Large whales produce and hear low-frequency sounds.
Examples: Blue whale, Fin whale, Bowhead whale.
Estimated functional hearing range: 7Hz – 36,000Hz
Low-frequency hearing allows baleen whales to communicate and detect sounds across vast ocean basins, but it also means their hearing overlaps strongly with commercial shipping noise, making them particularly vulnerable to masking.
Toothed cetaceans (odontocetes)
Toothed whales, including dolphins and porpoises, use sound extensively for both communication and echolocation, but their hearing abilities vary widely amongst species.
Estimated functional hearing ranges differ substantially across odontocetes, reflecting different ecological strategies and acoustic niches. Some species, such as killer whales, are most sensitive to mid-frequency sounds, while others, including beluga whales, have broad hearing ranges that extend into high frequencies. Harbour porpoises are extreme specialists, with hearing tuned to very high frequencies used for narrow-band echolocation.
Because of this diversity, odontocetes may be affected by human-generated noise in different ways, depending on the frequencies involved and the context of exposure.
Examples: killer whale, bottlenose dolphin, beluga whale, harbour porpoise.
Estimated functional hearing range: ~0.25 kHz to well above 100 kHz, though sensitivity peaks vary by considerably by species.
Sources: National Research Council, 2003; Mooney et al. 2012.
Pinnipeds
These semi-aquatic fin-footed marine mammals have a wide hearing range adapted for both air and water.
Examples: Harbour seals, Steller Sea lions, Northern elephant seals.
Estimated hearing range: approximately 150Hz – 40,000Hz, varying by species and medium .
Because pinnipeds rely on sound in both environments, they may be affected by noise both underwater and at the surface, particularly in nearshore habitats. Notably, harbor seals and California sea lions show aerial hearing sensitivity comparable to terrestrial carnivores, while also hearing nearly as well underwater as fully aquatic mammals – suggesting they have not sacrificed hearing in one medium to gain sensitivity in the other.
Source: Reichmuth et al., 2013.
Fish
Hearing abilities in fish vary greatly among species and depend strongly on anatomy – particularly whether a gas-filled body such as a swim bladder is coupled to the inner ear, which can extend hearing sensitivity. Research on fish hearing, including in elasmobranchs (sharks and rays), is more limited than for marine mammals, and existing data should be interpreted with caution due to significant methodological challenges in measuring fish hearing accurately. Available studies suggest most species hear primarily at low frequencies, with hearing typically extending to no more than 800–1000 Hz, though this varies considerably by species.
Examples: Atlantic cod, salmon, dab.
Estimated range: up to ~800–1000 Hz for most species, though this is highly species-dependent (Popper et al., 2019).
These low-frequency ranges overlap extensively with vessel noise, raising concerns about masking, stress, and behavioural disruption.
Source: Popper et al. 2019
Invertebrates
Marine invertebrates are sensitive to underwater noise, even though many lack structures that resemble vertebrate ears. Rather than detecting sound pressure, invertebrates primarily sense particle motion – the physical movement of water particles – through specialized organs such as statocysts and superficial hair cells.
Examples: Mantis shrimp, spiny lobster, ghost crabs, barnacles, squid, and bivalves.
Estimated hearing range: generally below 3,000 Hz, with some species sensitive up to ~5,000 Hz.
Although less studied than vertebrates, noise impacts on invertebrates may include physical damage to sensory organs, disrupted development, altered behaviour, and increased mortality, with potential cascading consequences throughout marine food webs.
Sources: Solé et al., 2023; Nedelec et al., 2016)
Why hearing ranges matter
The overlap between human-generated noise and the hearing ranges of marine species determines how disruptive that noise can be. When noise overlaps with frequencies used for communication, navigation, or foraging, it can interfere with an animal’s ability to survive and reproduce.
This overlap sets the stage for acoustic masking, behavioural change, and long-term population-level impacts – explored in the next section.
Impacts of underwater noise on marine life
Underwater noise can affect marine animals in multiple ways, depending on the source, intensity, frequency, duration, and distance from the noise, as well as the biology and behaviour of the species exposed.
Impacts range from short-term behavioural changes to long-term consequences that may affect survival and reproduction.
1. Acoustic masking
Masking occurs when one sound makes it harder to hear another sound of interest by overlapping in frequency, timing, or both.
Masking is often described as “acoustic fog.” Just as visual fog makes it harder to see important landmarks or visual cues, acoustic fog makes it harder for animals to detect and interpret sounds they rely on. The sounds are still present, but they are blurred or obscured by background noise, reducing how far and how clearly signals can be perceived.
For marine animals that depend on sound to communicate, find food, and navigate, masking can thus reduce access to critical information, even when the noise itself is not loud enough to cause physical harm.
Examples include:
- Baleen whales, whose low-frequency calls overlap strongly with noise from commercial shipping
- Toothed whales, whose communication signals or echolocation clicks may be masked by nearby vessel noise
- Fish, whose low-frequency hearing often overlaps with boat and engine noise
Because masking reduces the communication range or listening space of animals, it can:
- interfere with coordination between individuals
- make prey harder to detect
- disrupt navigation cues
Because masking depends on relative sound levels (the signal-to-noise ratio), even moderate increases in background noise can create significant acoustic fog and substantially reduce the distance over which animals can hear and be heard.
What does masking sound like? Try it yourself
The Noise-O-Meter below presents real underwater audio recordings at different noise levels, alongside the real listening space reduction that those noise levels cause for killer whales. Each sound clip is a real, unedited 8-second recording from Boundary Pass, randomly selected from a full year of acoustic data collected by SIMRES at Monarch Head on Saturna Island in 2025. The sounds are played at their true relative volumes: louder recordings genuinely are louder, not artificially amplified. As you move up the noise scale, watch the Available Listening Space shrink – this is the real, calculated reduction in the acoustic space available to a killer whale at that noise level for communication – measured in the frequency range of 500 Hz to 15 kHz, the band killer whales use to communicate with one another.
2. Behavioral disturbance
Many marine species change their behaviour in response to underwater noise. These responses may be brief or prolonged and can include:
- altering vocal behaviour (e.g., calling louder or changing call structure)
- interrupting feeding or resting
- changing dive patterns or movement paths
- avoiding noisy areas altogether
In some cases, animals exhibit what is known as the Lombard effect — increasing the amplitude of their calls in noisy conditions. While this can help maintain communication, it may also increase energetic costs, reduce communication efficiency, and increase detectability to predators or competitors.
Repeated or chronic disturbance can reduce the time animals spend feeding, resting, or caring for young.
3. Displacement and habitat degradation
When noise levels remain high over time, animals may avoid or abandon otherwise suitable habitat.
This can effectively reduce the amount of usable habitat available, even in areas that appear healthy based on food availability or physical conditions.
Displacement has been documented or inferred in:
- marine mammals avoiding busy shipping lanes or ports
- fish altering habitat use near noisy infrastructure
- changes in species distribution in chronically noisy areas
From a conservation perspective, this represents a form of habitat degradation that is invisible but biologically meaningful.
4. Physiological stress
Noise exposure can activate stress responses in marine animals, leading to changes in stress hormone levels and other physiological processes.
Chronic stress may:
- suppress immune function
- reduce reproductive success
- impair growth or development
While measuring stress in free-ranging marine animals is challenging, growing evidence suggests that persistent noise exposure can contribute to long-term health effects, particularly when combined with other stressors such as food limitation or contaminants.
5. Hearing injury
Very loud sounds (particularly impulsive noises such as pile driving or certain sonar signals) can cause temporary or permanent hearing damage in marine animals.
Potential effects include:
- Temporary Threshold Shift (TTS): a reversible reduction in hearing sensitivity
- Permanent Threshold Shift (PTS): irreversible hearing loss
Hearing injury is most likely:
- close to the sound source
- at high sound levels
- when animals cannot move away
Although these effects are relatively rare compared to masking or disturbance, they are of serious concern due to their potential severity.
6. Population level consequences
Most individual noise impacts — masking, disturbance, stress, and displacement — do not act in isolation. Over time, repeated exposure can lead to population-level effects by:
- reducing foraging efficiency
- lowering reproductive success
- increasing vulnerability to other threats
These cumulative effects are particularly concerning for:
- endangered or small populations
- species with slow reproduction
- animals already stressed by reduced prey or habitat loss
WATCH:
Why cumulative effects matter
Underwater noise is often chronic, widespread, and increasing, meaning that many marine animals are exposed repeatedly over long periods rather than in isolated events.
Over time, repeated masking, behavioural disturbance, and displacement can reduce feeding efficiency, increase energetic costs, and limit access to critical habitat. These effects may not be immediately visible, but they can accumulate and affect survival and reproduction.
Noise also interacts with other stressors such as reduced prey availability, chemical pollution, and climate-driven habitat change, potentially amplifying their combined impacts on marine life.
Understanding and managing underwater noise is therefore an essential part of protecting marine ecosystems and supporting long-term species recovery.