Understanding Underwater Noise Pollution: Causes And Effects

Underwater noise pollution is a growing concern for marine life, as it interferes with the critical activities of marine species, such as breeding, foraging, and maintaining social structures. Caused by human activities such as commercial shipping, oil exploration, and military sonar, this form of pollution can obscure natural sounds, disrupt behaviours, and hinder communication. The impact of noise pollution on marine life is severe and wide-ranging, affecting marine mammals' hearing, causing stress, and even leading to death. With noise levels in some ocean regions doubling every decade since the 1950s, there is an urgent need for regulations and measures to reduce underwater noise pollution and protect marine ecosystems.

Commercial shipping

The impact of commercial shipping noise on marine life is twofold. Firstly, the noise itself can cause direct harm to marine animals, including hearing loss and increased anxiety levels. Secondly, there are indirect effects, such as the disruption of breeding, foraging, social structure maintenance, and predator avoidance. These impacts can be immediate and severe or accumulate over time.

The problem of underwater noise pollution from commercial shipping is exacerbated by the fact that sound waves travel faster in water, covering greater distances than in air. This means that increased noise levels from ships affect marine animals and habitats far beyond the immediate vicinity of the source. Additionally, the complex and interconnected nature of marine ecosystems means that the effects of noise pollution on one species will indirectly impact others.

To address this issue, international institutions and organisations like the International Maritime Organization (IMO) have developed guidelines for reducing underwater noise from shipping. These guidelines include strategies for noise reduction in design, construction, modification, and operation, such as reducing ship speeds. While these guidelines are voluntary, some local governments and ports have implemented their own regulations, such as the Port of Vancouver offering discounts to vessels that comply with environmental guidelines.

Overall, the increasing noise pollution from commercial shipping has severe consequences for marine life, and efforts to mitigate these impacts and protect sensitive habitats are crucial.

Oil exploration

In addition to seismic surveys, other oil exploration activities such as ship engines, underwater blasts, and sonar also contribute to underwater noise pollution. As ships crisscross the oceans, their engines emit noise that can interfere with the communication of dolphins and other marine mammals. The use of sonar by navy vessels in search of new oil sources also emits sounds that penetrate deep into the ocean, increasing noise pollution.

The impact of oil exploration on underwater noise pollution is not limited to the immediate area of operation. Noise travels much faster in water than in air, meaning increased noise levels can affect marine life and habitats far from the source. Even in remote regions like the Arctic, which was once off-limits to most human activity, global warming has led to increased shipping traffic and oil exploration, bringing new levels of noise pollution.

To address the issue of underwater noise pollution caused by oil exploration, better regulation and the implementation of mandatory guidelines are necessary. While some local governments and individual ports have established their own regulations, such as the Port of Vancouver offering discounts for vessels that comply with environmental guidelines, more widespread and stringent measures are needed. International organizations like the International Maritime Organization (IMO) have developed guidelines for reducing underwater radiated noise from shipping, but these are not always effective or mandatory.

Seismic surveys

The noise from these surveys has been associated with impacts on many marine taxa, including mammals, crustaceans, cephalopods, and fish. There has been a significant effect on cetaceans, with an 88% decrease in sightings of baleen whales and a 53% decrease in sightings of toothed whales during active seismic surveys. Some species-specific responses to noise have been observed, with fin whales, humpback whales, and blue whales all showing behavioural changes in response to airgun noise.

Seismic blasts can cause damage to the hearing organs of cetaceans, resulting in temporary or permanent hearing loss. This can mask communication and the ability of animals to hear and avoid danger, putting whales at greater risk of ship strikes or separation from their calves or pod. The noise can also cause stress and behavioural changes, such as avoidance and hearing threshold shifts. In some cases, loud sounds from human activities have caused whales to strand and die on beaches, which then affects seafloor-dwelling animals that rely on the whale's body for food.

The increasing global coverage and large noise propagation distances of seismic surveys suggest that their effects on marine life are likely to increase. This must be considered when assessing species distributions and designating protected areas, especially with the additional threats of climate change and habitat loss. There are currently no international standards for the regulation of ocean noise pollution, although some local governments and individual ports have established their own regulations. However, international institutions are beginning to take notice, with the United Nations Convention on the Law of the Sea (UNCLOS) seeking to prevent and reduce marine pollution from vessels and the International Maritime Organization (IMO) establishing guidelines for the reduction of underwater radiated noise from shipping.

Military sonar

The use of military sonar can lead to injury and even death among marine wildlife. In January 2005, for example, 34 whales from three different species stranded and died along North Carolina's Outer Banks during nearby Navy sonar training. This is not an isolated incident, as there have been other cases of whale strandings and deaths linked to sonar testing.

Whales have been observed to rapidly change their depth in response to sonar, sometimes leading to bleeding from the eyes and ears, and even beaching themselves to escape the sound. The frequency used in military testing can be harmful to some animals, causing them to panic and surface more frequently for air. For example, whalers have equipped their boats with sonar at a frequency of 3000 hertz, which causes whales to pant at the surface, making them easier targets.

The impact of military sonar on marine mammals has been a subject of debate and legal conflict, particularly in the United States. Environmental groups have lobbied the government to curtail testing or ramp it up gradually to give marine wildlife a chance to escape affected areas. In 2003, the Natural Resources Defense Council (NRDC) successfully sued the Navy to restrict the use of low-frequency sonar off the coast of California. However, the Supreme Court later ruled that the Navy could continue some mid-frequency sonar testing for national security reasons.

The conflict surrounding military sonar use highlights the tension between protecting marine life and addressing national security concerns. While regulations and mitigation strategies are necessary to reduce the impact on marine ecosystems, finding a balance between these interests remains a challenge.

Construction noise

Offshore wind farm construction, such as the piling of large monopiles or jacket foundation pinpiles, generates significant underwater noise. The construction process involves the use of heavy machinery and pile-driving, which produce intense sounds that propagate through the water. The size of the pile, the power of the pile driver (hammer), and the sedimentological and geological properties of the site all influence the amount of noise produced.

The Belgian North Sea wind farms provide a case study in the impact of construction noise. Two wind farms, the C-Power project and the Belwind project, utilised different foundation types, resulting in varying levels of underwater noise emissions. The C-Power project, which employed jacket foundations, generated higher noise levels than the Belwind project's monopile foundations. The zone of major behavioural disturbance for harbour porpoises was estimated to be 8 km around the jacket piling location, while it extended to 16 km from the monopile piling location.

The construction of these wind farms resulted in increased underwater noise levels, with the C-Power project emitting 20 dB re 1 µPa more during its operational phase. This increase in noise can have significant impacts on marine mammals, interfering with their natural behaviours and communication. The loud sounds can cause hearing loss, stress, and changes in feeding and vocalisation patterns.

To address the issue of construction noise, policymakers and organisations are working towards implementing noise reduction measures. For example, the International Maritime Organization (IMO) has established guidelines for reducing underwater radiated noise from shipping, recognising its adverse impacts on marine life. These guidelines include strategies for noise reduction in design, construction, and operation, such as ship speed reduction. Additionally, local governments and ports have established their own regulations, with incentives for vessels that comply with environmental guidelines.

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