Noise Pollution: A Harmful Intrusion In Water Ecosystems

Noise pollution is an invisible danger that can have harmful effects on human health, wildlife, and environmental quality. While noise pollution is commonly generated inside many industrial facilities and some other workplaces, it also comes from road, rail, and air traffic, as well as human activities in the ocean. In this context, underwater noise pollution has emerged as a significant issue, adversely affecting marine life and the natural ecosystem.

How does noise pollution affect whales and dolphins?

Noise pollution in the ocean has increased dramatically in recent decades, which is extremely damaging to marine wildlife as most species depend on sound for survival. Whales and dolphins are particularly affected by noise pollution, as they rely on sound for key life functions such as communication, locating food and mates, avoiding predators, and navigation.

Noise pollution can interfere with these natural sounds, disrupting their behaviours and ability to communicate. For example, increased ship noise has caused bottlenose dolphins to simplify their vocal calls, making it harder for members of the same species to recognize each other and find mates. It also makes it more difficult to communicate the presence of predators or prey. Dolphins rely on echolocation to hunt and navigate, and noise pollution can cause them to become separated from their pods, leading to displacement or fragmentation of populations, which in turn makes it harder for them to hunt and reproduce successfully.

Noise pollution can also cause behavioural changes in whales and dolphins, driving them away from important feeding or breeding grounds and forcing them to alter their migration routes. For instance, there is evidence of behaviour changes among humpback whales more than 120 miles away from loud noise sources. Blue whales have also been observed to stop feeding, increase their swimming speed, and move away from the sound source in response to noise pollution, which can have significant impacts on their individual fitness, foraging ecology, and population health.

Loud noises can also cause immediate damage to whales and dolphins, such as hearing loss, and in some cases, even death. For example, beaked whales are extremely sensitive to sound, and when they hear loud noises, they dive recklessly, sometimes resulting in death from the bends. Additionally, loud ocean noise like naval anti-warfare sonar can directly injure whales and dolphins, causing them to panic and try to escape too quickly, leading to stranding or decompression sickness.

Overall, noise pollution poses a significant threat to whale and dolphin populations, interrupting their normal behaviour, driving them away from areas important to their survival, and in some cases, even causing injury or death.

How does noise pollution impact the behaviour of marine animals?

Marine animals have evolved over millions of years to use underwater sound as a primary means of communication and assessing their environment. As visibility is often low underwater, sound plays an essential role in critical activities for marine species, like breeding, foraging, maintaining social structure, and avoiding predators.

Noise pollution in the ocean has increased dramatically in recent decades, which is extremely damaging to marine wildlife as most depend on sound for their survival. Noise pollution can interfere with the detection of acoustic signals in the marine environment, masking the sounds produced by marine wildlife. This can lead to changes in individual and social behaviour, altered metabolisms, hampered population recruitment, and can subsequently affect the health and service functions of marine ecosystems.

Research from a 2006 study found that temporary and permanent hearing loss in marine mammals resulted in a reduction in foraging efficiency, reproductive potential, social cohesion, and ability to detect predators. Another study conducted in Southern California showed that even at sound levels much lower than those of military sonars, blue whales stopped feeding, increased their swimming speed, and moved away from the sound source. This can have significant impacts on the whales’ individual fitness, foraging ecology, and population health.

Noise pollution can also cause marine mammals to change their vocal behaviour. For example, increased ship noise caused bottlenose dolphins to simplify their vocal calls, with higher whistle frequencies and reduced whistle complexity recorded. This simplification may reduce the information content of their calls and decrease effective communication. Marine mammals may compensate for noise by making their signals longer, increasing the volume of their calls, shifting their sound frequency, or waiting to signal until the noise has gone. However, these changes can be costly, and noise pollution is having negative effects on many marine species, especially when combined with increasing pressures from climate change and overfishing.

How does noise pollution affect the ocean ecosystem?

Noise pollution is defined by the World Health Organization (WHO) as noise above 65 decibels (dB). Sound becomes harmful when it exceeds 75 dB and is painful above 120 dB. The ocean ecosystem is particularly susceptible to noise pollution due to the fact that sound travels faster in water than in air. This means that the sounds produced by the thousands of vessels travelling across the global ocean at any one time can affect marine life far and wide.

Marine mammals like whales and dolphins are especially vulnerable to noise pollution. These animals rely on echolocation to communicate, navigate, feed, and find mates. Excess noise, therefore, interferes with their ability to effectively echolocate. Some of the loudest underwater noise comes from naval sonar devices, which work by sending pulses of sound down into the ocean depths to bounce off objects and return an echo to indicate their location. Sonar sounds can be as loud as 235 dB and travel hundreds of miles underwater.

Noise pollution can also drive marine life from their habitats, impairing their ability to communicate, feed, reproduce, and avoid predators. It can even result in injury or death. For instance, if a whale strands on a beach in response to sudden, intense noise from a human activity, the whale dies on land instead of at sea. Its body does not sink to the seafloor, depriving seafloor-dwelling animals that rely on the whale's body for food and sustenance of a key food source.

There is considerable evidence to suggest that anthropogenic sounds impact marine mammals' behaviour underwater. For example, a 2016 study found that humpback whales in an area with chronically elevated shipping traffic changed their foraging activity when exposed to elevated ship noise.

Initiatives to reduce noise pollution in the ocean include the European Union setting mandatory thresholds for underwater noise to protect species and habitats, and the IFAW's Blue Speeds campaign, which aims to reduce ship speeds in Europe.

What are the sources of underwater noise pollution?

The sources of underwater noise pollution are varied and wide-ranging. Human-made noise is the primary cause, with most human activities on or in the water generating noise. The natural soundscape of the ocean—the wind, waves, and vocalizations of whales and other marine life—is being drowned out by anthropogenic noise.

One of the major sources of underwater noise pollution is commercial shipping. The noise from a ship's propeller cavitation, hull vibrations, and diesel engines can cause significant disruption. In particular, the bubbles generated by excessive propeller speed implode and create noise that can be extremely damaging to marine life. The low-frequency sound produced by ships, typically from 10 Hz up to 1 kHz, can overlap with the frequencies used by whales, which range from 10 to 31 Hz, depending on the species. The increased shipping traffic in previously pristine areas like the Arctic Ocean has led to a doubling of underwater noise levels in just seven years.

Another significant contributor to underwater noise pollution is the use of sonar equipment. Sonar, an acronym for "sound navigation and ranging," comes in two types: passive and active. Passive sonar listens for underwater sounds, while active sonar emits sounds to detect and locate objects using returning echoes. Active sonar systems are primarily employed by the military and can cause hearing loss in fish and disorient whales, leading them astray from their pods or calves. Even at lower sound levels, blue whales have been observed to alter their behavior in response to sonar, stopping feeding, increasing their swimming speed, and moving away from the sound source.

Seismic surveys, used to identify areas for oil and gas exploration, also generate excessive noise. Seismic air guns produce low-frequency sounds that can extend for thousands of kilometres and last from seconds to months. These blasts interfere with the communications of underwater species and compromise the ability of some whales to use echolocation to map their environment and find food. The continuous noise can also mask the ability of animals to hear and avoid danger, increasing the risk of ship strikes.

Other human activities that contribute to underwater noise pollution include industrial construction, warfare, seabed mining, offshore wind farm construction, and recreational boating. Dynamite fishing, a practice used in Southeast Asia and coastal Africa, is a major source of blasting noise. Even activities intended to be climate-friendly, such as constructing offshore wind farms, can substantially increase local sound levels.

What are the solutions to underwater noise pollution?

There are several solutions that can help mitigate the harmful effects of underwater noise pollution on marine life.

One of the most significant contributors to underwater noise pollution is shipping, with propeller noise accounting for about 85% of shipping-related noise. To address this, shipping companies can invest in redesigning and retrofitting their vessels with more efficient and quieter propellers. For example, the Danish shipping company Maersk spent over $100 million in 2017 to retrofit 11 of its container craft, resulting in a significant reduction in acoustic output. While this option may be costly and out of reach for smaller companies, it is an effective way to reduce propeller cavitation, which causes a breakdown in water flow over the blades, leading to increased noise, fuel inefficiency, and wasted energy.

In addition to propeller redesign, shipping companies can also implement slower shipping speeds, which has been shown to reduce underwater noise levels and emissions of greenhouse gases and other pollutants. This strategy was inadvertently demonstrated in the aftermath of the September 11, 2001 terrorist attacks, when ship traffic in the Bay of Fundy, Canada decreased, resulting in a drop in underwater noise levels by six decibels.

Another solution is to reroute vessels away from sensitive marine ecosystems and densely populated areas of the ocean. This approach not only reduces the impact of noise on marine life in those areas but also creates quieter periods that may benefit whale communication and behaviour.

To address the impact of seismic surveys used to locate oil and gas reserves, a technique called marine vibroseis can be employed. This method uses more continuous and lower-amplitude signals, reducing the sound generated during the detection of fossil fuel deposits.

Additionally, the introduction of acoustic "curtains" or bubble curtains can be used to dampen noise associated with offshore wind farms and energy generation stations. These curtains act as a barrier, reducing acoustic energy output and providing a barrier between the noise source and the external area.

While these solutions do not provide a definitive cure for oceanic noise pollution, they represent meaningful steps towards mitigating its most detrimental effects and restoring the health of the global ocean soundscape for marine life and humans alike.

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