While vessel design is important, immediate noise reduction is best achieved through operational changes
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In the dark undersea world, sound is essential. Marine life relies on sound for communication, foraging, reproduction, and navigation. However, as human activity in the oceans increases, so does underwater radiated noise. Various industries contribute to ocean noise—offshore energy, construction, military operations, and of course vessel traffic. With growing activity from commercial shipping, offshore developments, fishing and recreational vessels, underwater noise from vessels is increasing.
This increase has consequences for marine life, particularly species that rely on sound to survive, such as marine mammals. Underwater noise can mask natural sounds, which may make it difficult for animals to communicate, find a mate or prey, or even avoid predators. Some may change their behaviours, such as communicating less or avoiding or abandoning habitat. Underwater noise may also increase stress or have other health impacts.
In response to these concerns, Transport Canada’s Quiet Vessel Initiative supports research to reduce underwater vessel noise. The Quiet Vessel Initiative provides federal funding for research and development projects to advance and test promising technologies, vessel designs, retrofits and operational practices to make vessels quieter and more efficient, contributing to the protection and recovery of the marine environment and endangered marine mammals.
This series of articles explores the results and shares the challenges identified by some of the Quiet Vessel Initiative-funded projects.
How can ships be quieter in the water?
Designing quieter vessels, with hulls, propellers, and engines optimized to reduce noise, is a critical step toward reducing underwater noise. However, operational decisions play a crucial—and more immediate—role in lowering noise levels. As explored previously, for most vessels, the greatest contributor to underwater vessel noise can be propeller cavitation – when water undergoes a rapid change from liquid to vapour because of pressure changes caused by propeller rotation. The change from liquid to vapour creates bubbles, or cavities, in the water – hence “cavitation.” The collapse or implosion of these cavities causes high-frequency noise. If vessels can slow down to below cavitation inception speed (the speed at which propeller cavitation starts), the amount of noise may be significantly reduced.
One example of intentional operational change is the Vancouver Fraser Port Authority’s ECHO (Enhancing Cetacean Habitat and Observation) program, which asks ship operators to participate in an annual voluntary slowdown to reduce underwater vessel noise during the summer months when Southern Resident killer whales are most likely to be present in the Salish Sea, a key area of critical habitat for these whales. This program has high participation rates and reduced underwater sound intensity by up to 34%, or 1.8 decibels, in Boundary Pass in 2024, as measured by the Boundary Pass Underwater Listening Station. Another way for vessel operators to protect whales is by subscribing to the Ocean Wise Whale Report Alert System to receive real-time alerts about whale detections made by cameras, hydrophones, and people in the area where they are transiting. With better information about whale movements, mariners can take action to reduce noise and avoid impacts to whales.
Learn more about the Boundary Pass Underwater Listening Station
Killer whales – a species at risk from underwater vessel noise
Killer whales are iconic to Canada’s Pacific coast and hold deep cultural significance for Indigenous Peoples and coastal communities in British Columbia. Three distinct populations of killer whales are found in the coastal waters of British Columbia: Southern Resident and Northern Resident killer whales, separate populations that feed on fish, preferring Chinook salmon; transient or Bigg’s killer whales that feed on marine mammals such as seals; and offshore killer whales that are believed to feed on sharks and fish. Under the Species at Risk Act, Southern Residents are designated as Endangered, Northern Residents and Bigg’s are designated as Threatened, and the offshore population is listed as a Species of Special Concern.
The Endangered Southern Residents’ critical habitat in the Salish Sea is also frequented by vessels of all sizes, from small pleasure craft and ferries to cruise and cargo ships. Several other whale populations are often seen in the area as well. Approximately 74 whales remain in the Southern Resident population1, reduced from a peak of 98 in the mid-1990s, since tracking started in 1976.2 Their decline is primarily attributed to three factors – a decline in Chinook salmon, their primary prey; increases in contaminants in the ocean; and an increasingly noisy underwater environment. Acoustic and physical disturbances are considered among the most pressing threats to Southern Resident killer whale survival and recovery.3 Dedicated recovery strategies have been in place since 2019,4 and even in the most optimistic scenario, where human activities do not increase mortality or decrease reproduction, the recovery of Southern Resident killer whales is expected to take more than one generation (about 25 years).
Learn more about the Southern Resident killer whales and what can be done to help them.
Operators of both small and large vessels can reduce their noise footprints through operational changes. Several Quiet Vessel Initiative projects explored operational changes that vessel operators could implement to reduce their vessel’s underwater noise. Some changes are more relevant for large vessels while others are more applicable to small vessels due to different operational patterns and constraints.
Defining large and small vessels
Vessels commonly considered as large include container ships, freighters, passenger ferries, cruise ships, and even large fishing vessels that often travel far from the coast and over great distances. Large vessels can affect large areas of the ocean with continuous, low-frequency noise from their engines and other machinery, and high-frequency noise from cavitating propellers. As described previously in this series, sound, particularly low-frequency sound, can travel farther underwater than in air. Large vessels tend to be spread out in the open ocean and are more concentrated along near-shore shipping lanes and anchorage areas near ports.
Smaller vessel types can include tugs, fishing boats, recreational or pleasure craft, tour boats, dive boats, and other tourism vessels outside of cruise ships. Small vessels can be quieter than large ones, but there is generally no consistent linear relationship between vessel size and noise emissions. Further, small vessels can congregate in high numbers in a given area, resulting in a large cumulative temporal noise impact. In addition, small vessels tend to stay closer to the shore and in waters less than 200 metres deep, where sound can be reflected from the ocean floor, and where marine life is more abundant. Taken together, the noise impact of small vessels in coastal areas can be significant, particularly during the summer season when whales are more often present in Canadian waters.
Learn more about how sound travels through the water and changes due to ocean floor and other oceanographic conditions, from the first article in this series, Technology for Detecting and Analysing Underwater Radiated Noise.
This article was prepared by Clear Seas on behalf of Transport Canada as part of the Quiet Vessel Initiative and is part of a four-article series on operational changes to limit underwater vessel noise.
Continue learning about the new discoveries and challenges in making vessels quieter with the other topics in this series here
The Quiet Vessel Initiative is a federally funded program through Transport Canada. Industry partners and researchers interested in potential research and development collaborations to advance innovative solutions in marine technology are invited to contact the Quiet Vessel Initiative team at Marine-RDD-maritime@tc.gc.ca.
References
- Center for Whale Research Photographic Population Census, July 1, 2025. ↩︎
- Independent Science Panel on SRKW Recovery (2025). Strengthening recovery actions for Southern Resident killer whales. https://doi.org/10.70766/32.7300, pg. 13. ↩︎
- Independent Science Panel on SRKW Recovery (2025). Strengthening recovery actions for Southern Resident killer whales. https://doi.org/10.70766/32.7300, pg. 28. ↩︎
- Independent Science Panel on SRKW Recovery (2025). Strengthening recovery actions for Southern Resident killer whales. https://doi.org/10.70766/32.7300, pg. 16-17. ↩︎
Cavitation: a change in phase from liquid to vapour, like boiling, but caused by a change in pressure rather than a change in temperature. When areas of sufficiently low pressure are generated in water, vapour bubbles (cavities) form. As the vapour bubbles leave the area of low pressure, they collapse (implode).
Because the pressure differences are usually large, the collapse of cavitation bubbles is very powerful and loud. Other vessel factors, such as the hull design, also influence cavitation.
Measurements have shown that propeller cavitation is more common at higher speeds due to greater loads on propeller blades. Cavitation can also occur when propeller blades are misaligned or damaged. In addition to creating a great deal of sound, cavitation bubbles can damage or degrade metallic surfaces like propellers, reducing their performance and efficiency.
Commercial shipping: Vessels engaged in the transport of goods or people for the purpose of economic trade, including (but not limited to) container ships, bulk cargo carriers, vehicle carriers, tankers, cruise ships and ferries.
Frequency: sound moves through a medium like water as a wave, thus the term sound wave. Frequency, also known as pitch, indicates how often a sound wave repeats within a single second. Measured in Hertz (Hz), or cycles per second, higher numbers signify higher-pitched sounds, and lower numbers signify lower-pitched sounds.
Marine life: Mammals, fish, and invertebrates living in the ocean environment.
Mask, masking: A phenomenon where one or more sounds influence how another sound is perceived. This interference makes it difficult for the listener to accurately grasp and identify the sound of interest, causing it to become harder to understand. Masking can occur underwater when background noise, such as waves, wind, rain, or human activities, interferes with the detection or communication of sounds of interest and importance to marine life.
Oceanographic conditions: physical and chemical features of the ocean that vary in space and time. They include factors such as temperature, salinity, currents, waves, tides, ice concentration and thickness, and surface winds.
Propeller, cavitation: When a propeller turns, it creates a low-pressure area on one side of the blade and a high-pressure area on the other. In many cases, the pressure in the low-pressure area is low enough to cause cavitation, a change in phase from liquid to vapour, like boiling, but caused by a change in pressure rather than a change in temperature. When areas of sufficiently low pressure are generated in water, vapour bubbles form. As the vapour bubbles leave the area of low pressure, those bubbles collapse (implode).
Because the pressure differences are usually large, the collapse of cavitation bubbles is very powerful and loud. Other vessel factors, such as the hull design, also influence cavitation. Measurement efforts have shown that propeller cavitation is more common at higher speeds due to greater loads on propeller blades. Cavitation can also occur when propeller blades are misaligned or damaged. In addition to creating a great deal of sound, cavitation bubbles can damage or degrade metallic surfaces like propellers, reducing their performance and efficiency.
Retrofit: replacing or modifying a ship’s original structure, engine, or other equipment with newer models or technology to improve the ship’s performance, such as increased energy efficiency, reduced greenhouse gas emissions, or reduced noise emissions. One example of a common retrofit for ships is the installation an exhaust gas cleaning system (scrubber) to be compliant with the IMO 2020 sulphur emissions reduction regulation.
Underwater noise: sound generated below water by human activity in the ocean environment. Various industries contribute to underwater noise—offshore energy, construction, military operations, and of course vessel traffic. The noise generated by vessels is referred to as underwater radiated noise.
