Ocean Noise Pollution: Understanding Its Causes

Marine animals have evolved to rely on sound as a primary means of communication and environmental assessment. However, human activities such as commercial shipping, oil exploration, seismic surveys, and military sonar are causing noise pollution in the ocean, threatening marine life. This noise pollution can interfere with marine animals' natural behaviours, communication, and ability to navigate, leading to disorientation, injury, and even death. With ocean traffic increasing, addressing noise pollution is crucial to protecting marine ecosystems and the animals that depend on them.

Commercial shipping

Most of the underwater noise caused by commercial shipping is due to a ship's propeller cavitation—the bubbles that are generated and implode due to excessive propeller speed. The basic rule is: the bigger and faster a ship, the louder it is. Cargo ships can emit as much as 190 decibels of noise, which is much louder than a plane taking off and about the same noise level as a rock concert. Another big source of ocean noise pollution produced by ships is hull vibrations and the vessel's diesel engines. Ships produce a low-frequency sound that goes from 10 Hz up to 1 kHz. For reference, the range of frequencies used by whales goes from 10 to 31 Hz, although this varies from one species to another.

The impact of commercial shipping noise on marine life is tremendous. Marine mammals use underwater clicks, whistles, and songs to communicate with their young, search for food, find mates, and avoid dangers. But these sounds can be drowned out by the noise of ships. For animals that rely on echolocation, like dolphins and toothed whales, excessive noise can disrupt these signals, causing the animal to become disoriented and unable to hunt successfully. As well as disturbing essential life activities, noise can also indirectly cause injury. To escape the noise, animals might ascend too quickly, leading to decompression sickness and skin damage from gas bubble lesions.

Noise from commercial shipping can also cause hearing loss or even cause animals to strand and die. If a whale strands on a beach in response to sudden, intense noise from a ship, its body doesn't sink to the seafloor as it normally would. The seafloor-dwelling animals that rely on the whale's body for food then lose a key food source. Noise from commercial shipping has been shown to cause increased stress levels in right whales and to significantly alter the behavior of marine mammals, especially whales, affecting their feeding and hindering mother-calf communication.

There are ongoing efforts to reduce noise emissions from commercial shipping. The International Maritime Organization (IMO) is working on revising guidelines, with technical innovations and adaptations in shipbuilding being considered. It is expected that the revised guidelines will be issued in the summer of 2023. According to IFAW consultant and noise expert Russell Leaper, reducing the speed of the global shipping fleet by 10 or 20% would reduce noise emissions by 40 or 67% respectively. Such a measure would also have other positive environmental benefits, such as reducing CO2 emissions and lowering the risk of collisions with whales.

Military activities

The use of sonar by military vessels is a significant source of noise pollution within sanctuary waters. Sonar emits high-intensity and excessively loud signals, causing panic and disorientation in marine animals. The sudden increase in noise can lead to animals ascending too quickly, resulting in decompression sickness and skin damage from gas bubble lesions. It can also trigger stress responses, disturb nesting habits, affect coordination and navigation, and cause hearing damage.

Noise pollution from military activities can also have indirect effects on marine ecosystems. For instance, if a whale strands on a beach due to sudden, intense noise, its body may not sink to the seafloor, depriving seafloor-dwelling animals of a key food source. This demonstrates how noise pollution can have far-reaching consequences for marine life.

While there are currently no international standards for regulating ocean noise pollution, efforts are being made to address this issue. The International Maritime Organization (IMO) is working on revising guidelines to reduce noise emissions from shipping, and technical innovations in shipbuilding are being considered. Additionally, organizations like IFAW are campaigning to reduce underwater noise through legislative and local actions. These efforts are crucial for mitigating the impacts of military activities and other human activities on marine life and ecosystems.

Oil and gas exploration

The impact of this noise pollution on marine life is significant. It interferes with the natural sounds and communication of marine mammals, such as whales and dolphins, who rely on loud sounds, clicks, whistles, and echolocation for long-distance communication. The increased background noise from oil and gas exploration can mask these signals, making it difficult for them to find mates, coordinate within their groups, and care for their young.

Additionally, the loud noises can trigger stress responses in fish, disturb nesting habits, affect coordination and navigation, and cause hearing damage. In some cases, the sudden loud noises can lead to decompression sickness and skin damage as animals try to escape the noise by ascending too quickly.

The use of air guns for oil and gas exploration has also been linked to the disruption of marine ecosystems. For example, the blasts can kill juvenile krill and reduce fish catch rates, impacting the food sources for other marine life. The explosions created by these airguns can last for days to weeks, subjecting marine life to prolonged periods of acoustic disturbance.

To address the issue of noise pollution from oil and gas exploration, there is a growing focus on regulation and the adoption of quieter technologies. Global initiatives, such as the United Nations' efforts, aim to implement comprehensive frameworks for protecting marine biodiversity, including noise mitigation measures. Industries are also exploring quieter alternatives, and the shift towards renewable energy sources can help reduce the dependence on noise-intensive activities.

Seismic surveys

The noise from these air guns can also cause behavioural changes in marine mammals, such as whales, and interfere with their natural communication. For example, studies have shown that baleen whales are more vulnerable to disturbance from seismic airgun noise than toothed whales due to the overlap of frequencies with their communication signals and hearing sensitivities. There is also evidence of fewer sightings of toothed whales during active airgun periods of seismic surveys.

The impact of seismic surveys on marine life is of great importance, especially as dwindling fossil fuel reserves are driving the search for hydrocarbon resources further offshore. The noise created by these surveys can be considered a form of environmental pollution, and with over 60% of the global oceans experiencing increases in human impacts, underwater noise pollution is a significant issue.

Construction

Underwater construction activities, such as drilling, dredging, and pile driving, create massive amounts of noise emissions. The International Maritime Organization (IMO) has established guidelines for reducing underwater radiated noise from shipping, which include strategies for noise reduction in construction and operation. However, the original guidelines were not widely adopted by industry members, and a revised version is being developed to increase uptake and monitor effectiveness.

The impact of construction noise on marine life can be severe. Marine mammals, such as whales, dolphins, and porpoises, rely heavily on sound for communication, navigation, breeding, foraging, and maintaining their social structure. Construction noise can obscure natural sounds, disrupt their behaviours, and interfere with their ability to echolocate and communicate. In some cases, it can cause hearing loss, disorientation, and even strandings, leading to the death of marine mammals.

Additionally, construction noise can have indirect effects on the marine ecosystem. For example, if a whale strands on a beach due to noise pollution, seafloor-dwelling animals that rely on the whale's body as a food source will lose a crucial part of their diet. This demonstrates how noise pollution can have cascading consequences throughout the intricate ocean food web.

To mitigate the impact of construction on ocean noise pollution, several measures can be implemented. These include the development and use of quieter technologies, such as noise-reducing propellers, floating wind turbines, and "bubble curtains" that muffle construction noise. Policies and regulations that mandate acoustic mitigation in the marine environment are also necessary. By reducing construction noise and implementing better regulations, we can help marine life withstand the pressures of human activities and enable their potential recovery.

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