What is ocean noise pollution?
According to the World Health Organization, noise generated by human activities is a harmful driver of environmental change and is even recognized as a global pollutant. The alteration of acoustic underwater conditions caused by noise from human activities (i.e., anthropogenic noise), is called aquatic noise pollution, or ocean noise pollution when limited to the marine environment.
This noise can be the result of seismic exploration (e.g., oil and gas deposits location), military activities (e.g., explosives, sonar), anti-predatory devices (e.g., shark-shield devices), shipping traffic, industries and leisure activities. Even lower noise levels caused by other structures and devices (e.g., marine renewable energy devices) can cause significant disturbances in the environment, considering that low-frequency sonars can impact an area of approximately over 3.9 km2.
How does noise pollution affect marine biodiversity?
Although noise pollution is invisible, it is a threat to both animals and biodiversity that can sometimes even be deadly. Noise pollution has been linked by researchers to negative impacts on fauna development, physiology and behavior. A combination of human population growth, urban development, economic growth and other anthropogenic changes (e.g., climate change, environmental structure change) is making the ocean noisy and results in environmental degradation. Ocean noise can further directly affect sound propagation, making it more difficult for animals to communicate for the purpose of feeding, reproducing, nursing, migration, acoustic masking and other essential behaviors to survive. Many marine species are found to suffer from cumulative noise effects, in some cases resulting in more bycatch and collisions with ships.
A variety of animal groups is potentially affected by noise pollution such as vertebrates, invertebrates and anything from crustaceans to fish and marine mammals (e.g., whales, dolphins, manatees, otters, sea lions, and seals). Moreover, some species may be affected indirectly because their prey is stressed by noise pollution and moves away or dies. Thus, due to chain-effects, the marine environment may be negatively affected to a greater extent than is visible at first sight. The number of studies on this issue has increased over the years and resulted in a better understanding of both the different sources and most affected species: marine mammals and fish, which is due to their use of sound as their primary sense.
Massive stranding events are often associated with active use of sonar technologies. Since the 1960s, more than 40 mass strandings were reported for only one whale species, the Cuvier’s beaked whale. More than half of these occurred during the use of naval sonar or close to naval bases. Whales were found to have died of brain and heart haemorrhage which could be a result of navigation issues due to the effects of noise on the animals. With sublethal noise levels, other effects could be noticed on whale populations, such as changes in migration routes, alterations in foraging practices, and changes in the call patterns.
Seismic air guns were shown to affect fish hearing within a 500 meters radius. This could be responsible for a long-term hearing recovery process, abnormal stress-related hormonal rates, abnormalities in motion reaction, lower reproductivity rates, changes in occupancy areas, and major alterations of their natural physiology (e.g., embryo development) and behavior (e.g., settlement or migration activities). These impacts on marine biodiversity can generate issues for local economies, once fisheries and tourism are affected by the reduction of fish stocks and the abandonment of the area by species in some cases.
Dead Gray’s beaked whale (Mesoplodon grayi) after stranding with five other individuals. Image by Avenue.
What has been done about it?
Ocean noise research began to increase and gain some importance around the 1940s. Many pieces of research about this topic have been developed to provide recommendations and directions for further studies, policy-making processes, mitigation initiatives and to highlight ways to understand and control this invisible hazard.
Passive acoustic monitoring techniques may assist in the understanding of the noise pollution influence on marine fauna. An international project called “Listening to the Deep Ocean Environment” allowed researchers to monitor ocean noise and marine mammal sounds. The data gathered helps to clarify the acoustic influences and to create mitigation actions, at least in key-areas for ocean conservation. To mitigate this type of pollution, some suggestions have been made based on marine spatial planning to identify and register key areas for protection and stronger controls. These areas are a priority for mitigation measures and are called “Quiet Marine Protected Areas”, (Q-MPAs) and may be used as sanctuaries by the animals.
The International Ocean Noise Coalition (IONC) was created to build a global plan to fight against and reduce human-generated ocean noise. Over 150 international organizations work as a group to raise awareness and advocate for finding ways to address this issue. With the beginning of the IONC movement, international bodies and agreements started to recognize and address human ocean noise, such as the United Nations by adding ocean noise pollution as one of the major impacts on marine biodiversity to the UN Convention on the Law of the Sea in 2005, the International Maritime Organization with their recognition of the harmful effects of ship-generated ocean noise in 2010, and the International Whaling Commission, which included ocean noise as a priority issue back in 2009.
What about the future?
Studies about ocean drilling, seismic blasting, shipping and sonar usage are needed to assess their effects on the region where they are planned to be practiced. With that, organizations and institutions fighting for the ocean can create and support campaigns and actions (e.g., lawsuits against owners/governments/agencies, development of policy-making processes and creation of Q-MPAs).
As ocean enthusiasts, we can support research by donating to projects and actions, taking part in events and calling for a global strategy to reduce underwater noise pollution (e.g., by signing petitions) and sharing content from organizations, institutions and groups that stand by the ocean and its inhabitants.
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