Course:EOSC270/2021/Underwater Noise: sources and impacts on marine life
What is the problem?
Since noise travels very efficiently in water, ocean noise pollution is a global issue. Marine sonar can affect ecosystems up to 3.9 million km away. The loudest noise tends to be near areas of increased human activity. Figure 1 shows the frequency of which certain shipping paths are used. Whales and dolphins have been documented changing their migration paths to avoid oil drilling, and shipping lanes. Military sonar has been documented to kill animals, and postulated to genetically-isolate some whale groups.
Ocean noise pollution has many causes, strictly speaking any human activity that directly involves the ocean increases ocean noise. Some of the greatest contributors to today’s noise pollution are commercial shipping (fig.1), seismic surveys, oil drilling (Fig. 2), military sonar, and coastal construction.
Sound is the predominant method of communication and environmental awareness in the ocean. Most marine animals use sound to detect their surrounding environment and communicate with each other over long distances. Marine mammals use sound to hunt and mate. Marine invertebrates and fish use sound as a defense display and for mating purposes. This is because 1) light only penetrates the upper 200m of the ocean making vision an unreliable form of communication, and 2) sound travels very efficiently in water (four times more efficiently than in air), making it easy and fast for communicating. The increase of human activity in/around the ocean has caused the ambient noise level to increase dramatically. The increased noise in the ocean interferes with the normal sound-biology of all marine animals. Reproduction, predator avoidance, long distance communication, and biological development are all extremely effected by the increase in ambient noise. Increased rates of internal injury, metabolic activity, stress hormones, disease, and DNA damage have also been linked to more ocean noise.
Noise in our oceans has increased substantially in the last few decades with no evidence of stopping. Due to the global scope of anthropogenic marine activities, noise pollution is an issue effecting many, if not all marine ecosystems. The survival of many marine animals depends on their ability to emit and hear sounds, but noise pollution threatens this. This problem’s effects are only now beginning to be seen in marine communities, and if nothing is done, we could see global shifts/collapses in marine ecosystems.
How does this problem impact marine ecosystems?
Why ocean ecosystems
Whale whistles, waves crashing, sea urchins rasping are all part of the natural soundscape of the ocean. Soundscape as defined by Schafer is the auditory environment which contains a variety of sounds and their sources; containing both natural and anthropometric noises. The marine soundscape is complex both in the fact that noise travels farther in water as compared to on land and marine life is highly sensitive to sounds. As international trade climbs, noise pollution also increases in frequency and distribution as boat traffic grows. Other sources of human-caused noise also have notable impacts such as seismic surveys, and the sounds produced by oil and gas platforms. This problem and the effects will continue to grow and impact the marine ecosystem in industrialized areas.
Many marine creatures use sound as their main sense rather than vision, as sound can travel far and faster underwater as compared to land, and vision is often heavily limited . This makes marine organisms more susceptible to the effects of noise pollution. Sonar, used for seismic exploration, is defined as high-intensity noise and has been documented to have caused physical damage even towards large creatures such as cephalopods to the degree of massive internal injuries.
Direct impacts on marine life
Even low-intensity chronic noise generated by boat traffic is often linked to auditory masking. Auditory masking occurs when one sound is overlaid by the presence of another, affecting an organism's perception of it. Many marine organisms rely upon sound to hunt, detect prey, and communicate. An experiment conducted on three fish families found that auditory sensitivity was lower in fish exposed to ambient noise that masked sounds around them.
Noise pollution does not affect all ocean habitats equally. Coastal ecosystems are high in biodiversity and make up most of the life in the oceans  while also being heavily trafficked. Noise pollution likely affects the majority of creatures in these ecosystems. Whales in coastal and open ocean habitats have shown significant negative effects that are attributed to noise pollution due to being extremely sensitive to sounds. In the days following 9/11 as boat traffic was greatly reduced; the stress level measured among Right Whales in the bay of Fundy (Figure 3) was notably lower. The whales produced fewer stress hormones under circumstances of decreased noise level of up to 6dB. Once boat traffic returned to normal patterns the measured amount of stress hormones raised back up to levels beforehand.
Increased noise pollution from anthropometric sources disrupts the marine soundscape by effecting communication within species, behavioral patterns, physiology and overall health. These effects, while negative, can aid in increasing our understanding of the importance of marine soundscapes.
What is the extent of the problem?
Effects on the ecosystem
Noise pollution has a negative effect on marine ecosystems in multiple ways. One of these effects is reducing the ability of ocean animals to communicate. Communication is an essential tool for many processes in marine organisms. Potential mates, young, and group members all require the use of sound to communicate with each other, and their ability to do this is reduced by higher noise levels. However this isn’t the only use of sound that becomes affected by sound pollution. Repelling predators and foraging are two other processes that involve the use of sound, and higher level noises also greatly reduce the abilities of marine organisms to execute these actions. Some whales have even left their regular feeding and breeding areas as a result of noise pollution. The direct effects of even moderate noises can potentially be fatal. The Cuvier’s beaked whale species experienced over 40 mass strandings across the globe after the emergence of more powerful sonar in 1960. The cause of deaths for whales appears to be brain and heart hemorrhaging, possibly a result of the stress response to noise leading to alternate diving patterns and decompression sickness. Sensitivity to noise has also been found to likely be a heritable trait, so even when organisms impacted by noise manage to find a mate, their offspring might already be sensitive to noise. Fish can undergo temporary or even permanent hearing loss, in addition to reduced catch rates. While not all effects of noise pollution on marine mammals are fatal, some may find themselves in an unfamiliar habitat without proper means of returning to their original habitat. These effects exemplify the consequences of noise pollution in marine ecosystems, its impact on genetic diversity, and how important it is that there is still an adequate amount of organisms with good hearing.
Extent of the problem compared to the past
It is extremely likely that noise pollution from humans has resulted in these negative effects on marine ecosystems. The previously mentioned Cuvier’s beaked whale mass strandings had a severe increase only after more powerful sonar started appearing in 1960. While over 40 mass strandings were reported between 1960 and today, the species only had one mass stranding reported between 1914 and 1960. One beaked whale population was well-studied and it was found that for years after a sonar-induced stranding, the population numbers were declining, with many members of the local population likely being displaced or even killed. The effects of noise pollution appear to be much worse when compared to the past.
What will happen in the future?
If not reduced, noise pollution will continue to lower the fitness of marine organisms, through disrupting the ability for these animals to communicate and hear. Continued lowering of these organisms’ fitness could also lead to their extinction, further disrupting the ecosystems. Organisms that appear to experience direct, fatal effects, such as certain species of whales, will likely continue to die off as a result of noise pollution and also risk going extinct.
Many marine species are highly migratory and disregard borders and regions we have created and therefore a global perspective is important in management and data acquisition. Local context and local drive are equally important. While acknowledging that underwater noise we generate has widespread negative impacts, there are ways to mitigate the problem.
In Canada several research projects and initiatives are underway to better understand underwater noise and the impacts on marine life. They are led by governmental agencies, universities, industry, Indigenous communities and non-governmental agencies.
Canada’s Oceans Protection Plan is offering funding for research projects to better understand the impact that shipping-related noise has on Southern Resident Killer Whales. Canada’s Oceans Protection Plan is offering funding for research projects to better understand the impact that shipping-related noise has on Southern Resident Killer Whales. The Plan proposes voluntary measures for vessels to reduce noise and speed and, sets to organize national and international technical workshops to promote adopting quiet ship design standards and technologies.
The Port of Vancouver has its own noise-reduction initiatives and incentives. Through the EcoAction Program for instance, discounts on harbour fees are offered to vessels that have adopted emission (including noise) reduction measures.
The United Nations recognized the problem in 2018 at the Convention of Migratory Species. It was then agreed that more research on the impacts of Underwater Radiated Noise should be put forward to mitigate ocean noise when and where possible. The International Maritime Organization has also addressed adverse impacts on marine life by putting together non-mandatory guidelines for mariners to reduce underwater noise from commercial shipping. Recommendations include reducing speed, rerouting to avoid sensitive marine areas, habitats or migratory pathways as well as improving design, maintaining and optimizing vessels.
Addressing impacts of shipping: Design and optimization
Commercial marine traffic is one of the main sources of anthropogenic underwater noise. Cavitation has been identified as the principal source of noise radiated by ships, followed by machinery noise. Cavitation occurs due to low pressure generated by propellers which forms tiny air bubbles. It occurs commonly but in excess, can cause unwanted wear and noise when those air bubbles collapse. It is possible to reduce cavitation by adjusting propeller and hull design, propeller and hull interaction or machinery configuration.
The design phase was found to be where there is the greatest opportunity to make a difference. Underwater noise prediction models can help analyze noise sources on a ship and their pathways of transmission. The models can be used by shipowners, shipbuilders and designers to identify appropriate noise control measures such as vibration isolation mounts, dynamic balancing, structural damping, acoustical absorption and insulation, hull appendages and propeller for noise reduction, variable pitch propellers.
Underwater noise is a pervasive problem partly because of the lack of awareness and of its invisible nature. It interferes with marine life, notably marine mammals in their rest, hunting, communication, mating, navigating and overall awareness. For the past 60 years, noise has doubled in intensity every decade in the North Pacific Ocean, with the exception of 2020 which has seen a downward trend due to the pandemic  .
There are technologies to reduce underwater noise pollution such as bubble curtains and hydro sound dampers which are used for offshore pilings. Other strategies include reducing and optimizing marine traffic, rethinking our global trade policies, and our own consumption habits.
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