About ocean noise and its impacts

On this page

• Notes
• Importance of sound in the ocean
• The science of sound
• Understanding sound in the marine environment
• Human activities and sources of ocean sound
• Categories of impacts on marine wildlife
• How different marine species respond to ocean noise
• Impacts of ocean noise on human cultural and societal practices
• Reducing complex ocean noise impacts
• Glossary
• References

Notes

Although the physics of sound in the ocean is well understood by the scientific community, the manner in which sound functions in the marine environment and the associated effects of noise on marine animals can be a very complicated issue to describe. In fact, many aspects related to impacts are not fully known. Readers may wish to consult the list of references in this document for more information on ocean noise.

While this document was primarily informed by western scientific findings associated with ocean sound, noise and its impacts, the Government of Canada acknowledges the need for and importance of Indigenous Knowledge systems in understanding and managing ocean noise management. Readers may wish to consult the draft Canada's Ocean Noise Strategy for more information on the Government of Canada's efforts to better understand and manage ocean noise.

Linked terms identified in text are glossary terms. For the definition of these terms, please click to go to the Glossary section of the document.

Importance of sound in the ocean

Sound is crucial to life under water. Although acoustic communication is important for many terrestrial animals, it is even more important for marine animals because sound travels very efficiently underwater.^{Footnote 1} The ocean has a rich natural soundscape that is made up of natural biotic and abiotic sounds. Natural biotic sounds include:

• whale calls
• dolphin whistles
• fish grunts
• other sounds that are produced by marine wildlife

These biotic sounds are used for:^{Footnote 2}

• communication
• foraging
• mating
• avoiding predators

Abiotic sounds include those from non-living sources, such as:

• waves
• cracking ice
• undersea volcanos

This combination of sounds makes the ocean an extremely dynamic environment where the ability for marine animals to send and receive sound signals is vital for their survival.^{Footnote 3},^{Footnote 4},^{Footnote 5}

The science of sound

Sound is a type of energy created by the vibration of molecules. As energy is transferred between molecules, the movement generates sound-pressure waves that can travel through a medium, such as air or water. In short, sound is the term used to describe what is heard when these pressure waves are received and interpreted by recipients.

Sound is often described by its amplitude (or loudness) and frequency (or pitch). To the human ear, higher frequencies are perceived as higher-pitched sounds; larger amplitudes are perceived as louder sounds. As sound travels through a medium, it loses energy which limits its travel distance.^{Footnote 6} Loud sounds have more acoustic energy than quieter sounds. Low-frequency sounds lose less energy while they travel, allowing them to travel further than higher-frequency sounds.^{Footnote 7} That is why loud and low-frequency devices such as foghorns are commonly used to communicate over long distances. Similarly, a blue whale call, which is also very loud and low frequency, can be detected hundreds of kilometres away.^{Footnote 8}

Understanding sound in the marine environment

Sound behaves differently in water as compared to air due to the difference in physical properties of these 2 media. Sound can travel approximately 4.5 times faster in seawater than in air (1450 to 1550 metres per second in saltwater compared to 343 metres per second in air).^{Footnote 7} Sound speed also increases with the salinity of the water making the ocean an extremely efficient transmitter of sound. This characteristic makes sound a highly effective and reliable means of communication in water, especially when compared to sight (vision is often limited to tens of metres at best underwater)^{Footnote 9},^{Footnote 10} or smell (odours are often intermingled because of the turbulence of ocean waters).^{Footnote 11}

Other factors such as water temperature and pressure (which varies with depth), salinity, seafloor compositions and structure and other oceanographic conditions, including the amount of ice cover and sea state, can also influence how fast and how far sounds travel. Studying these relationships allows scientists to better understand the characteristics of sound in the marine environment.

Temperature, salinity and pressure

Temperature, salinity and pressure impact the speed that sound travels underwater. Sound speed increases with increases in temperature and pressure, and these vary greatly depending on depth (Figure 1). The interacting effects of temperature and pressure mean that sound travels the slowest at approximately 500-1000 metres in depth where temperature and pressure are relatively low. This horizontal zone of minimum speed is called the SOFAR (SOund Fixing And Ranging) channel. Similarly, sound travels faster in water with increased salinity. In areas where freshwater inputs (such as estuaries or from the melting of glaciers) are present, sound in water would travel slower than the other marine areas if all other factors are the same.

Water depth, seafloor composition, ice cover and other oceanographic conditions

Sound travels differently depending on water depth. Every time the sound waves interact with either the ocean surface or seafloor, some or all of the acoustic energy gets reflected or absorbed.^{Footnote 13} In shallow waters, sound waves have an increased number of interactions with the surface and seafloor, which results in increased loss of acoustic energy. The amount of absorption or reflection of sound depends on the bottom composition of the seafloor and the sea state.^{Footnote 13} In ice-covered conditions, sound is partially absorbed by sea ice and is reflected or scattered based on the smoothness of the underside of the ice. As a result, sound loses energy more rapidly and does not travel as far in polar regions when sea ice is present.^{Footnote 14},^{Footnote 15}

Human activities and sources of ocean sound

The development of the global marine economy over the last 200 years has increased the number of sources and overall loudness of human-generated (or anthropogenic ) ocean sounds, completely changing the coastal and offshore underwater ocean soundscape (Figure 2).^{Footnote 17}

While there are many human activities in the marine environment that produce sound over a wide range of frequencies, there are 6 main categories of activities that produce the majority of underwater ocean sound, which are described below.

When examining the sounds created by these activities, it is important to consider 4 aspects of the noise source:

1. the amplitude (or loudness) of the source
2. the frequency range of the source
3. whether the source is producing continuous or impulsive noise
4. the extent of source, including how common the activity is in an area at which it can impact marine life

Large vessels

Large ocean-going vessels, such as container ships, bulk carriers, coastal freighters, ferries and cruise ships are, collectively, the largest human source of low-frequency underwater sound.^{Footnote 17} While these vessels produce a variety of sounds, the most significant sound source is the low-frequency continuous sound from the ship's propeller.^{Footnote 18},^{Footnote 19} This low-frequency range is critical for many marine species as they use it to communicate with and locate each other, sometimes over great distances.^{Footnote 17} These sounds contribute to the background of anthropogenic sound over large geographical areas.^{Footnote 20},^{Footnote 21}

Small vessels

Smaller vessels, such as, fishing vessels, pleasure craft and tourism vessels (excluding cruise ships), are another significant source of continuous sound that span a broad range of frequencies. These vessels are plentiful and often found close to shore in waters of less than 200 metres where there is significant absorption and reflection of sound. Some small vessels, such as tugs, produce comparable levels of sound to large vessels; whereas other small vessels, such as tourism vessels and pleasure craft, produce less sound individually than large crafts, but the high number of these vessels and their presence in shallower waters can contribute to significant increases in anthropogenic sound in coastal areas.^{Footnote 22},^{Footnote 23},^{Footnote 24},^{Footnote 25},^{Footnote 26},^{Footnote 27}

Seismic surveying

Marine seismic surveys are often used for geological research and oil and gas exploration. These surveys use airguns that rapidly release compressed air. The collapsing air bubbles create a very loud and intense impulsive sound directed towards the seafloor; the reflected sound waves are used to identify subsurface geological features.^{Footnote 28} Seismic surveys can vary in intensity and frequency range depending on the purpose of the surveys.^{Footnote 29},^{Footnote 30}

Industrial activities and construction

Pile driving, dredging, drilling, tunnel boring, marine renewable energy and canal-lock operations are all examples of industrial and construction activities that contribute to underwater sound in the ocean and along shorelines. This diverse group of activities can release both high-intensity and impulsive sound (e.g., impact pile driving) as well as low-intensity and continuous sound (e.g. dredging, vibratory pile driving) into the marine environment.^{Footnote 9},^{Footnote 31}

Military activities

Military operations, such as ship-shock trials (where explosives are purposely detonated near a vessel to simulate a near miss during battle), live-fire exercises and operations using military sonar, all result in very high sound levels. Operations involving explosions are impulsive sounds, whereas naval sonar is a short continuous sound that is often repeated frequently. These activities contribute some of the loudest and most intense anthropogenic sound in the marine environment.^{Footnote 21},^{Footnote 32}

Echosounders and sonars

The use of echosounders for scientific, industrial, and recreational purposes is steadily increasing. These systems typically create an impulsive acoustic signal to seek information about objects (such as fish) within the water column, at seafloor or within the sediment. Unlike seismic airguns, these signals use a transducer to create a sound wave rather than using compressed air. Moreover, echosounders and sonars typically transmit signals in much higher frequency bands than seismic airguns (Figure 3). The use of these systems in the marine environment is pervasive and they can operate in a wide range of frequencies.^{Footnote 33}

Categories of impacts on marine wildlife

At any given time and place, the combination of natural and anthropogenic sounds can create a highly variable soundscape. While marine animals have adapted to changes in natural marine sounds, loud and intense anthropogenic ocean noise is relatively new.^{Footnote 17},^{Footnote 21},^{Footnote 34} While sound is any vibration that travels through a medium, noise is specifically unwanted or harmful sound.^{Footnote 35} Ocean noise can interfere with essential biological and ecological functions and can cause a wide range of impacts on marine wildlife.^{Footnote 36},^{Footnote 37} It is important to note that the behavioural impact of noise on marine animals is likely context-driven.^{Footnote 38} For example, age, sex, location, activity and prior noise exposure of the individual animal can all influence how that animal responds to anthropogenic noise.^{Footnote 39},^{Footnote 40},^{Footnote 41}

There are 4 general categories of ocean noise impacts on marine life:

Masking

Sounds from different sources at similar frequencies can interfere with one another making accurate interpretation of sound signals difficult. Masking occurs when noise interferes with a sound or signal of interest and decreases the animal's ability to detect, recognize or understand that sound. Anthropogenic ocean noise may mask sounds, such as those from prey, predators and mates that are vital to marine animals. Researchers have found that animals have trouble using sound for communication when anthropogenic noise is loud and occurs in similar frequencies, time and space as the animal's own acoustic signals (Figure 3).^{Footnote 42},^{Footnote 43} Given the widespread nature of human activities, masking may be one of the most extensive and significant impacts on the acoustic communication of marine organisms.^{Footnote 44}

Physical injury

Intense noise exposure may cause physical injury, including temporary or permanent hearing impairment and potentially even death. While all animals have different hearing ranges, animals exposed to intense sound have been shown to be unable to detect signals in their entire hearing range for a period of time following exposure.^{Footnote 46},^{Footnote 47} Although the magnitude of this impairment normally decreases over time, noise exposure can sometimes result in permanent hearing damage.^{Footnote 48} This permanent inability to detect signals at particular frequencies could impair vital life functions to the point where the animal's survival is jeopardized.

Physiological impacts

Noise may have various physiological impacts, including increased stress,^{Footnote 49},^{Footnote 50},^{Footnote 51} changed metabolic rates,^{Footnote 52} weakened immune system responses,^{Footnote 53} and reduced reproductive rates.^{Footnote 54} Extended exposures and repeated increases in stress could have long-term health impacts on marine animals.^{Footnote 55}

Behavioural changes

Noise exposure may cause behavioural changes and interruptions of normal activities,^{Footnote 56},^{Footnote 57} including changes in acoustic communication (or vocalizations), withdrawal from feeding or social interactions, changes in movement or diving behaviour and temporary or permanent habitat abandonment.^{Footnote 58},^{Footnote 59},^{Footnote 60} Over the long term, any permanent behavioural change could impact an animal's ability to find food and reproduce.^{Footnote 61} In severe cases, noise can also cause acute and severe reactions, such as panic, flight, stampeding or stranding, which can result in the animal's injury or death.^{Footnote 10}

How different marine species respond to ocean noise

A growing list of scientific studies confirms that noise generated by human activities in or near the ocean can cause a multitude of negative impacts on many different marine species. While most of the research to date has centred on cetaceans,^{Footnote 62} there are many other studies focused on understanding the impacts of ocean noise on other marine species. In fact, a recent review of 538 studies of the impacts of anthropogenic ocean noise confirmed that noise negatively affected many different species of marine animals^{Footnote 17} at the individual, population and community levels by affecting interactions between individuals of the same and different species.^{Footnote 63},^{Footnote 64},^{Footnote 65}

The following sections highlight some of the ways noise affects:

• marine mammals
• marine fishes
• invertebrates
• sea turtles
• seabirds

Marine mammals

Field studies have found that marine mammals respond to ocean noise exposure in a variety of ways. In the past, primary research tended to focus more on evaluating physiological responses, physical injury and mortality, but it has broadened in recent years to consider noise impacts on behavior and acoustic communication. Hearing impairment, masking, increased stress and displacement from preferred feeding areas are just some of the impacts that have been documented in a large number of marine mammals.^{Footnote 66},^{Footnote 67},^{Footnote 68} The consequences of these impacts are not always well understood but could include:^{Footnote 69},^{Footnote 70}

• reduced foraging success
• decreased social bonding
• failure to avoid predators

All of these effects have the potential for cascading and cumulative impacts on survival and reproduction, both at the individual and population level.^{Footnote 17},^{Footnote 71},^{Footnote 72} For cetaceans in general, while Figure 3 illustrated that they communicate over a large frequency range, most individual cetacean species only communicate over a narrower frequency range and they are often categorized into 3 groups:^{Footnote 48}

• low frequency (baleen whales) cetaceans
• high frequency (toothed whales and most dolphins) cetaceans
• very high frequency cetaceans (porpoises and a few dolphins)

These differences are also important when considering the impact of noise on cetaceans as they are sensitive to different types of noise based on their hearing range.

Marine fishes

Research has shown that in response to noise marine fish can change their behaviour, experience elevated stress levels, impaired abilities to detect predators, reduced foraging capacities and temporary hearing loss.^{Footnote 47},^{Footnote 56},^{Footnote 73},^{Footnote 74},^{Footnote 75} The number of different fish species and the variety of habitats that these fish occupy suggest that research on noise impacts should also consider individual physiologies and life cycles.^{Footnote 76},^{Footnote 77} For example, noise may have developmental impact on stationary nesting fish eggs compared to live birth fish.^{Footnote 78} Moreover, the presence of a swim bladder in marine fishes can also impact their sensitivity to noise. Fish with swim bladders have higher hearing sensitivity and tend to use sound more for communication, and they may be more impacted by ocean noise than those without swim bladders.^{Footnote 79}

Sea turtles

Compared to marine mammals and fishes, sea turtles have received very little research attention.^{Footnote 80} While recent research shows that freshwater turtles can experience temporary hearing impairment from an excess of ocean noise,^{Footnote 81} the highly migratory nature of sea turtles makes it difficult to study the potential impacts of ocean noise on this group of animals.^{Footnote 82}

Marine invertebrates

The term marine invertebrates encompasses a large number of animals that live in various ocean habitats including the water column and the seafloor.^{Footnote 83} These species (which include corals, sponges, sea urchins and molluscs, such as squid and mussels) are sensitive to sound transmitted through both the water column and the seabed.^{Footnote 84},^{Footnote 85},^{Footnote 86},^{Footnote 87} Several studies suggest that ocean noise may cause a variety of different impacts on these species:^{Footnote 88},^{Footnote 89},^{Footnote 90}

• animals may be distracted from finding food or shelter
• have an increase in stress-related chemicals
• have malformed embryos or
• suffer damage to hearing cells

High amplitude ocean noise, such as that from seismic surveys, can also cause a decrease in abundance of marine invertebrates such as zooplankton.^{Footnote 91}

Seabirds

There are very few studies on the potential impacts of ocean noise on seabirds, but a recent study found that diving birds such as common murres may be exposed to and affected by ocean noise when feeding.^{Footnote 92} It is worth noting that while seabirds only spend limited amount of time underwater, research show that they are sensitive to both in-air and underwater sound.^{Footnote 93},^{Footnote 94} Therefore, more complete evaluations of the potential ocean noise impacts on seabirds are needed.

Impacts of ocean noise on human cultural and societal practices

Anthropogenic ocean noise does not only have great impacts on wildlife, it also has an impact on many cultural and societal practices of coastal and Indigenous communities.^{Footnote 95},^{Footnote 96} For example, coastal communities and Indigenous subsistence hunting and fishing rely heavily on certain important marine species being available in specific habitats and at specific times. The presence of ocean noise can drive these species away, disrupt traditional practices and impact the pursuit of constitutionally protected Indigenous rights.^{Footnote 97}

Reducing complex ocean noise impacts

In addition to understanding how human activity creates noise and the characteristics of those individual sounds, it is also critically important to understand the impacts on marine wildlife when more than one human activity occurs in the same place at the same time. Simultaneous noise from multiple human activities can add to and interact with other marine stressors to increase the cumulative impacts on marine life.

While there is ongoing research on individual noise impacts on species, it remains extremely difficult to quantify the cumulative impact and interacting effects of so many different noise sources on any particular animal. The physical properties of noise, the biology and behaviour of the animals exposed to it and the circumstances around their exposure, are all important considerations that can interact with and influence the cumulative impacts of ocean noise on marine life.

Several examples in the scientific literature illustrate that the conditions and the health of impacted wildlife can improve quickly once noise levels decrease.^{Footnote 98} A 2012 study noted that a 6-decibel decrease in ocean noise in the Bay of Fundy (the result of reduced ship traffic following the events of September 11, 2001) reduced stress in right whales.^{Footnote 51} Several other studies found evidence that the reduction in noise from commercial shipping during the COVID-19 pandemic ^{Footnote 99},^{Footnote 100},^{Footnote 101},^{Footnote 102} was linked to an expansion of movements of marine mammals into busy harbours and coastal areas where they are not normally observed.^{Footnote 103},^{Footnote 104}

These particular research findings indicate that an improved understanding of noise impacts can support targeted efforts to address the causes of ocean noise. While more research is needed, the circumstantial evidence collected during these periods of severely reduced ocean noise does suggest that marine species respond positively to reductions in anthropogenic ocean noise.

This webpage has provided a brief and general overview of the characteristics of sound, ocean noise, and its impact. Readers are encouraged to further explore this topic and participate in any of the current and future Government of Canada collaborative initiatives to address this stressor. Given the complexity of ocean noise, it is crucial to continue research to better understand this topic. This will support the joint efforts of governments, organizations and communities in effectively managing anthropogenic noise sources to significantly mitigate their impacts on marine wildlife.

Glossary

Abiotic

Refers to something that is physical rather than biological, devoid of life.^{Footnote 105} In the context of an ecosystem, abiotic factors could include sunlight, temperature, wind patterns and precipitation.

Acoustic energy

The energy that travels through a substance in the form of sound waves is referred to as acoustic energy.^{Footnote 106} When sound passes through any medium, it creates waves of vibrations, which vary in their energy in proportion to the amplitude of the sound waves.

Amplitude

Refers to the height of the sound pressure wave or the “loudness” of a sound.^{Footnote 107} It is often measured using the decibel (dB) scale. Small variations in amplitude (“short” pressure waves) produce weak or quiet sounds, while large variations (“tall” pressure waves) produce strong or loud sounds. For example, imagine a wave on the surface of a pond. The amplitude would be the maximum height of the water above or below its calm level.

Anthropogenic

Caused and/or generated by humans.

Biotic

Refers to anything that is related to or resulting from living things, especially in their ecological relations.^{Footnote 108} It is the opposite of abiotic, which refers to non-living things in an ecosystem.

Continuous sound

A type of sound that is long-lasting and does not have impulsive characteristics.^{Footnote 109}

Cetaceans

Whales, dolphins and porpoises.

Cumulative impacts

The total changes to the individual animal, environment, health, social and economic conditions due to various human activities and natural processes happening over time and in different places. They include the additive effects of a project or development when combined with other past, present and foreseeable future activities.^{Footnote 110}

Decibel

A unit used to measure the intensity of a sound or the power level of an electrical signal. It is a relative unit, not an absolute one. Decibel is used to describe sounds in terms of their loudness.^{Footnote 111} For underwater ocean sounds, a reference pressure of 1 microPascal (μPa) is used to describe sounds in terms of decibel.

Frequency

Sound moves through a medium like water as a wave, thus the term sound wave. Frequency, also known as pitch, indicates how often a sound wave repeats within a single second. Measured in Hertz (Hz), also known as cycles per second, higher numbers signify higher-pitched sounds and lower numbers mean lower-pitched sounds.^{Footnote 10}

Hearing range

Particular range of sound frequencies that certain species are most receptive to.

Ice(berg) calving

The process or event that occurs when large slabs of ice detach from a glacier into the water.112 The sound waves generated by calving can be detected by microphones, seismometers and hydrophones, providing information about the frequency of calving events and the icebergs' size.^{Footnote 112} Iceberg calving is one of the main sources of natural ocean noise in polar regions and can be extremely loud capable of being perceived thousands of kilometres away.^{Footnote 113}

Impulsive sound

An acoustic signal with an instantaneous start and stop. Underwater impulsive sounds are generated by certain human activities, such as:^{Footnote 114}

• geophysical surveys
• impact pile driving
• acoustic deterrent devices
• multi-beam echosounders
• detonation of explosives

Intensity

The amount of energy contained in a sound wave, measured in a given area at a given time; this also translates to the subjective perception of sound pressure and loudness.

Logarithmic scale

A way of measuring data that grows exponentially. It is a relative unit, not an absolute one. The numbers on the axis are logarithms or powers of a base number, resulting in an exponential rise in value between units.^{Footnote 115} For instance, on a logarithmic scale with base 10, the distance from 1 to 10 is the same as the distance from 10 to 100 or from 100 to 1000.

Marine invertebrates

Marine animals lacking a vertebral column (or spine) and include animals, such as:

• shellfish (e.g., lobsters, crabs, clams, mollusks, etc.)
• sea cucumbers
• sea urchins
• corals
• many others

Marine stressors

Factors that affect the health and functioning of marine ecosystems.^{Footnote 116} They can be natural, such as earthquakes or storms, or caused by humans, such as fishing, pollution or climate change. The cumulative impact of various pressures in the ocean can result in a reduction in the ability of marine ecosystems to withstand and recover from these challenges. This can ultimately lead to a decline in biodiversity in marine environments.^{Footnote 117}

Mask (or masking)

A phenomenon where one or more sounds, typically a louder sound, influences how another sound is perceived. This interference makes it difficult for the listener to accurately grasp and identify the sound of interest, causing it to become less distinct and harder to understand.^{Footnote 42} Masking can occur underwater when background noise, such as waves, wind, rain or human activities, interferes with the detection or communication of sounds produced by marine animals or devices.^{Footnote 64}

Metabolic rate

The amount of energy that an organism expends over a specific period of time.^{Footnote 118} It refers to how quickly fuels such as sugars are broken down to keep the organism's cells running. The metabolic rate varies among species and depends on the environmental conditions and activity level of an individual organism.

Oceanographic conditions

Physical and chemical features of the ocean that vary in space and time. They include factors such as temperature, salinity, currents, waves, tides, ice concentration and thickness, and surface winds.^{Footnote 119}

Salinity

The amount of salt dissolved in a body of water. The speed of sound traveling through water tends to increase as salinity increases.^{Footnote 120}

Sea state

The general condition of the surface of the ocean related to waves and swells at a certain location and time. It is influenced by many factors such as winds, current and sea ice.^{Footnote 121} Sea state affects ambient sound levels, such that levels are lower under calm seas and higher under high sea states. It can also affect speed of sound in water, which in turn affects how far sound can travel before it becomes too weak to detect.^{Footnote 9}

Seismic survey

A geophysical operation that uses a seismic air source to generate acoustic waves that propagate through the water and sediment, are reflected from or refracted along subsurface layers of the sediment, and are subsequently recorded by hydrophones at the surface.^{Footnote 122}

Subsurface geological feature

Any geological structure or formation that is located below the surface of the earth. These features can include rock formations, mineral deposits and other geological structures that are not visible from the surface.^{Footnote 123} Subsurface geological features can be studied using a variety of geophysical techniques, such as seismic surveys.

Swim bladder

An internal air filled organ used by some fishes to control their buoyancy. It is also linked to the inner ear and can be used to make different sounds and acts as a detection mechanism for changes in sound pressure.^{Footnote 79}

Transducer

A device that converts electrical signals into sound waves or vice versa, for the purpose of generating or receiving ocean noise.^{Footnote 124},^{Footnote 125}

References