Ocean noise is a constant background in marine spaces. The arrival and departure of ships, the search for hydrocarbons, and the installation of offshore wind farms create a piercing racket that unsettles the seabed and its inhabitants. This is not just a nuisance; it disrupts communication among many fish and cetaceans that rely on sound for mating and feeding, and it can lead to direct harm in extreme cases. Scientists warn about the wide-reaching consequences of underwater noise and advocate for practical measures to reduce it.
To grasp how sound travels underwater, researchers note that with the right instruments, ships can be detected far from port, even when they enter or leave major harbors, sometimes thousands of kilometers away. This illustrates the far reach of human-generated sound beneath the waves.
One practical approach to cut the constant din is to slow vessels. A modest 11% reduction in speed can yield meaningful noise reductions. According to José Antonio Díaz, a Saturn consortium member and technician at the Canary Islands Ocean Platform (Plocan), ships remain the primary source of underwater noise, yet this small adjustment can have a substantial impact. Plocan is among twenty European centers contributing to the Saturn Europe project (Developing Solutions to Underwater Noise), which spent three years researching strategies to lessen underwater noise.
The project is led by the Science Foundation Ireland and coordinated by University College Cork, bringing together a broad European consortium with twenty partners across ten countries. The team comprises acoustic specialists, marine biologists, and marine engineers collaborating to identify effective solutions.
Most vessels travel at speeds between 20 and 24 knots; reducing speed by 11% would place them around 18 to 21 knots, a level that significantly eases the acoustic burden. Diaz notes that the noise largely stems from propellers rather than engines, and even a small speed adjustment can help.
“Contrary to what might be expected, ships make noise not because of their engines, but because of their propellers.”
When propellers turn, they generate bubbles that burst and produce a persistent, annoying sound that disturbs marine life. While slowing down is a strong short-term measure, Project Saturn researchers point out additional avenues, such as reshaping impellers to produce fewer bubbles and thus reduce noise.
Slower speeds offer other benefits as well. A 2019 assessment by Reynolds Environmental Sustainability Consultants (RESC) suggested that a 20% speed reduction could cut fuel use by more than 24%. Beyond shrinking greenhouse gas emissions, such reductions would lower noise pollution and cut cetacean deaths from ship strikes by substantial margins, underscoring the broader gains of quieter navigation.
Ship strikes remain among the most serious threats to sperm whales, pilot whales, and other large cetaceans, with injuries ranging from minor to fatal when collisions occur as animals cross busy routes.
The issue is acute in certain busy corridors. In Spain, the Strait of Gibraltar stands out as a hotspot where roughly 300 ships pass each day, translating to about one vessel every five minutes.
“Permanent or temporary deafness”
Ocean noise levels vary greatly. Díaz highlights a striking contrast between pristine, quiet regions and areas with intense economic activity and shipping. In some comparisons, the difference in noise can reach ten thousandfold. This disparity is described as barbaric by Saturn project researchers.
Relative to quiet, the human activity in busy seas resembles stepping from a natural soundscape into an environment dominated by machine noise. The Strait of Gibraltar again serves as a vivid example, underscoring how many ships traverse the area each day.
“There are places in the sea that are as noisy as being next to a plane about to take off”
Underwater noise affects all species. Historically, the focus has been on large mammals like cetaceans because their communication is sound-based. Two potential effects emerge: a direct physical impact that can cause temporary or permanent deafness, and a disruption of social communication when noise overlaps with the animals’ dialogue.
This interference makes it harder for individuals to hear one another, prompting displacement from noisy areas and, in some cases, from the group itself. Other fish species are also driven away from highly noisy zones, with cascading consequences for ecosystems and for human activities such as fishing.
Noise remains a relatively underaddressed problem, and researchers insist this is the moment to push for practical solutions and clearer measures that can be implemented.
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REPORT. Txema Brotons, marine biologist and scientific director of Tursiops
“The problem is that the sea is treated like a highway”
From a speed of 10 knots to a length of 90 meters, a boat can influence the risk to marine mammals
Underwater noise does not only threaten cetaceans through immediate visible harm. It also sustains chronic stress, lowering resilience to other pressures. Tursiops, an organization dedicated to researching this issue, continues to examine the full scope of the problem.
-To what extent does underwater noise affect marine mammals?
– The noise is mostly concentrated in the low frequencies where boats are heard most clearly. Low frequencies travel far and affect some species more than others. For example, a fin whale emits very low frequencies, while a dolphin uses higher ones. Chronic noise isn’t instantly lethal, but it raises stress and makes animals more vulnerable to other shocks, much like a wound becoming infected under stress.
-Can this noise cause death in some cases?
-Seismic surveys used in hydrocarbon exploration involve powerful underwater detonations that can be lethal to animals at a distance. Military sonar can trigger flight responses that lead to the direct death of deep-diving species.
-Can reducing speed effectively lower noise?
– Slower speeds not only cut noise but also reduce collision risk with marine mammals. As new ships sail, industries may be urged to design more efficient vessels. Sometimes a noisy ship indicates a malfunction. It is evident that the sea is treated as a highway, with implied dangers for wildlife and ecosystem balance.
-The other major issue is the collision of marine mammals with ships…
Large vessels carry the highest collision risk. A collision with a 12-foot boat differs greatly from one with a 25-meter yacht or a 120-meter ferry. Speed and size strongly influence survivability, with scientific work identifying thresholds that alter the outcome of a collision. In practice, maritime traffic patterns show higher risk up to a 10 nautical mile range and with ships longer than 90 meters. That does not mean smaller or slower ships are harmless, as ongoing expeditions have documented.
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