Meghan Hodges
Underwater noise pollution is a growing concern for marine life, with human activities such as shipping, boating, drilling, and military operations causing a significant increase in noise levels. This noise pollution has the potential to interfere with the critical life functions of marine mammals, fish, and other aquatic animals, who rely on sound to communicate, navigate, find food, and avoid predators. The impact of this pollution includes behavioural changes, hearing loss, injury, and even death. With noise levels continuing to rise, there is an urgent need to address this issue and implement measures to reduce its impact on marine ecosystems.
| Characteristics | Values |
|---|---|
| Causes | Explosives, oceanographic experiments, geophysical research, underwater construction, ship traffic, intense active sonars, air guns |
| Impact | Hearing loss, injury, death, changes in feeding, breeding, nursing, communication, sensing, and other behaviours vital to the survival of marine species |
| Solutions | Building new ships with quieting technology, ending seismic surveys for oil and gas, accelerating the transition towards (low noise) renewable energy sources, reducing ship speeds |
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What You'll Learn
Naval sonar devices
Sonar (an acronym for sound navigation and ranging) was first developed by the US Navy to detect enemy submarines. The technology was further developed by the British, French, and Canadians during World War I.
Sonar systems generate slow-rolling sound waves that can reach 235 decibels and travel for hundreds of miles underwater, retaining an intensity of 140 decibels as far as 300 miles from their source. These sound waves can lead to injury and even death for whales, dolphins, and other marine life. There is evidence that whales will swim long distances, change depth rapidly (sometimes leading to bleeding from the eyes and ears), and even beach themselves to escape sonar sounds.
Between 1996 and 2006, the use of active sonar was linked to around 50 marine mammal strandings. While other factors were at play, such as unusual underwater geography and specific species sensitivity, sonar was deemed the "most probable cause" in many cases. Beaked whales, in particular, are suspected to be highly sensitive to sonar.
Sonar devices play a dual role in ocean noise pollution. They are a significant source of underwater noise, especially in military and industrial operations. However, they are also essential for monitoring subsea noise levels and tracking underwater noise pollution. Passive sonar systems, which do not emit their own signals, are commonly used for this purpose, as they do not add to noise pollution.
The use of sonar by naval forces has been a subject of controversy, with environmental groups lobbying to restrict or curtail its use to protect marine life. In 2003, the Natural Resources Defense Council (NRDC) successfully sued the US Navy to limit the use of low-frequency sonar off the coast of California. While two lower courts upheld the NRDC's claims, the Supreme Court ruled in favor of the Navy, citing national security concerns.
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Shipping and vessel speed
Commercial shipping is the primary contributor to underwater noise pollution in the ocean. A cargo vessel emits around 190 decibels of noise, which is louder than a jet engine at takeoff. Noise travels faster in water, meaning that noise from a ship can impact a broad area of the ocean. The total carrying capacity of the global fleet nearly quadrupled between 1996 and 2020, with new and larger ships added to keep up with the growing global economy. As a result, noise from shipping is doubling roughly every decade.
Shipping noise emissions increase rapidly in Arctic areas and the Norwegian Sea. The largest contributors are container ships, dry bulk vessels, and liquid tanker vessels, which emit 75% of underwater shipping noise source energy. The COVID-19 pandemic temporarily disrupted the increasing noise emission trend, with a reduction of -6% in global shipping noise source energy.
The noise produced by shipping has detrimental effects on marine life, including fish, invertebrates, and marine mammals. Marine mammals rely on underwater sounds for essential life functions such as searching for prey, avoiding predators, locating offspring, and finding a mate. Underwater noise from ships can mask these natural sounds, causing marine life to leave their preferred habitats or change important behaviors. Studies have shown that ship noise can cause elevated stress in marine mammals, affecting reproduction and immunity, and even leading to death in some cases.
To mitigate the impact of shipping on underwater noise pollution, regulators have proposed several approaches:
- Reducing vessel speed: Slowing down ships can significantly reduce noise emissions. A general rule of thumb is that for each 1-knot reduction in speed, ship noise is reduced by 1 decibel. Optimized speed reductions in 2018 added only 9-15 minutes of travel time, depending on the vessel type.
- Technological modifications: This includes using propellers to decrease cavitation or tiny bubbles that make a loud noise when they burst, and ship-quieting technologies that can increase fuel efficiency and decrease environmental impact.
- Increasing the separation between vessels and animals: While this approach can be effective, it requires a good understanding of species habitat use and may not be feasible in restricted waterways.
Some governments have also taken measures to protect marine life from ship noise. For example, the Government of Canada installed underwater listening stations to learn more about the endangered St. Lawrence beluga population and introduced speed limits and minimum distance requirements for vessels in the presence of marine mammals. The Vancouver-Fraser Port Authority in British Columbia asks ships to slow down as they approach the port to reduce noise disturbance to the critically endangered Southern Resident orca population.
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Explosives and seismic surveys
Underwater noise pollution is a growing concern, with human activities such as shipping, seismic surveys, and sonar systems being major sources of noise. Marine life, from tiny shrimp to massive blue whales, relies on sound to navigate, find food, avoid predators, and communicate. This natural soundscape is being drowned out by human-made noise, causing a range of adverse effects on marine life.
The use of explosives and airguns in seismic surveys has been shown to have detrimental effects on a diverse range of species, including fish, invertebrates, plankton, and reptiles. Cetaceans, such as whales and dolphins, are particularly vulnerable to the noise produced by these activities. Studies have shown a reduction in cetacean sightings during active seismic surveys, with some species altering their migration routes due to increased noise levels.
The loud blasts from seismic surveys can cause acoustic and behavioural changes in whales, disrupting their singing and acoustic communication. Additionally, the low-frequency sounds generated by seismic airguns overlap with the communication signals of baleen whales, making it difficult for them to hear and understand each other. This can hinder their ability to find food, navigate, and avoid dangers, increasing the risk of ship strikes or separation from their calves or pods.
The intense noise produced by explosives and seismic surveys can also cause physical harm to marine life. Studies have shown that airguns can significantly reduce catch rates in fish and even cause internal injuries and death in certain species, such as narwhals and giant squid. The use of explosives can also result in brain hemorrhages, tissue trauma, and other serious injuries in marine mammals.
In conclusion, explosives and seismic surveys are significant contributors to underwater noise pollution, with far-reaching and detrimental effects on marine life. The increasing global coverage and noise propagation distances of these activities highlight the urgent need for regulations and precautionary measures to protect marine ecosystems and reduce the impacts of human-made noise on vulnerable species.
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Construction and infrastructure
In addition, coastal construction can also contribute to underwater noise pollution. This can include activities such as oil drilling, seismic surveys, sea-bed mining, and sonar-based navigation. Seismic surveys, in particular, can be extremely loud, as they involve blasting loud sounds into the ocean to map the sea floor. These blasts can cause damage to the hearing organs of marine mammals, resulting in temporary or permanent hearing loss.
The construction of new infrastructure in the ocean can also create a lot of noise pollution. For example, the propeller cavitation from shipping and the sonar used by navy vessels to search for new oil and gas sources can emit sounds that penetrate deep into the ocean. These sounds can disrupt the natural soundscape of the ocean, including the vocalizations of whales and other marine life.
The effects of underwater noise pollution from construction and infrastructure projects can be far-reaching. Noise levels in some ocean regions have doubled every decade since the 1950s, and this noise can drive animals out of their habitats and even kill them. It can also alter the behavior of marine mammals, affecting their hearing, causing stress, disrupting feeding, and hindering communication.
To mitigate these impacts, it is important to implement noise reduction measures and better regulate construction and infrastructure projects. This includes reducing ship speeds, as slower ships produce less noise pollution. It also involves adopting new technologies, such as noise-reducing propellers, floating wind turbines, and "bubble curtains" that muffle construction noise.
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Military operations
Sonar systems used in military naval operations send high-intensity pulses of sound into the ocean to detect submarines and map ocean floors. These sounds can reach and penetrate deeper depths than those produced by shipping or industrial activities. The impact of these sounds on marine animals can be disorienting and disruptive, interfering with their natural behaviours and senses. For example, research has shown that even at much lower sound levels, blue whales exhibited stress responses to active sonar, increasing their swimming speed and moving away from the sound source. This can have detrimental consequences for the whales' individual fitness, foraging ecology, and population health.
The use of naval sonar has been directly linked to mass strandings of whales, with the number of recorded strandings likely representing only a small percentage of the actual impact. The loud noises can cause immediate damage, such as hearing loss, and can even be fatal when sound is a primary tool for marine mammals' survival. For example, if whales or dolphins deep beneath the surface swim too quickly towards the surface to escape the noise, they can damage their eardrums, throw off their sense of balance and buoyancy, get the bends, or even die.
In addition to sonar, other military activities such as vessel sounds, seismic blasts, and explosions contribute to underwater noise pollution. These noises can have both immediate and long-term impacts on marine life, including behavioural and physiological changes, masking natural sounds, injury, and even death. The increasing noise pollution from military operations and other human activities is severely threatening the natural soundscape of the marine environment and the ability of marine wildlife to function and survive.
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Frequently asked questions
Underwater noise pollution refers to intense human-generated noise in the marine environment.
Underwater noise pollution is created by human activities such as shipping, seismic surveys, explosions, construction, and sonar devices.
Underwater noise pollution can have a range of negative effects on marine life, including temporary or permanent hearing loss, behavioural and physiological changes, masking of natural sounds, injury, and even death.
Some specific examples of how underwater noise pollution impacts marine species include altering the feeding behavior of endangered blue whales, causing mass strandings of beaked whales, and disrupting the communication and feeding patterns of marine mammals.
To reduce underwater noise pollution, governments and organizations are working to implement regulations and technological changes. For example, the WWF is advocating for mandatory regulations to reduce the impacts of underwater noise, while OceanCare is campaigning for a reduction in vessel speed, which can significantly reduce noise emissions.
