The ocean is usually thought of as a quiet place, but underwater noise pollution poses a real threat to marine life. Most people are unaware of the diversity of sounds constantly filling the seas, as the human being's hearing system is not adapted to identify this level of sound pressure. However, the ocean subsurface is teeming with communication, echolocation, and other natural noises important for ecosystems’ equilibrium.
Underwater noises from ships come primarily from propulsion motors and hull vibrations. Large cargo vessels and ferries usually rely on powerful diesel engines driving fixed-pitch propellers, which oscillate chaotically at high speeds. This cavitation effect bombards the surrounding waters with intense low-frequency pulses. Meanwhile, vessel hulls thrum constantly from mechanical operations. For whales, dolphins and other aquatic species that navigate through echolocation, these overlapping underwater noises can drown out important communication and environmental sounds over huge distances. Prolonged elevated noise has been shown to cause stress and disrupt natural behaviours in marine life, with implications on the breeding and survival rates. As ocean traffic builds, conservationists warn that the industrial acoustic footprint may overwhelm sensitive species' ability to thrive.
It is no different in the Salish Sea, an important habitat for the rich local biodiversity, including the Southern Resident Killer Whale species. Sustained elevation of background noise levels is thought to cause chronic stress that affects marine life’s behaviours, including reproduction and health. With vessel traffic projected to rise, further impacts on ocean habitats are of serious concern.
Thankfully, new technologies offer hope. All-electric passenger ferries have zero direct greenhouse gas (GHG) emissions and produce far less underwater noise. Without combustion engines vibrating the hulls and multiphase propeller flows developing cavitation, electric ferries are inherently quieter. Recent studies show electric ferries can emit noise levels more than 10 times lower than diesel-powered vessels.
For marine species surrounded by the din of ferry traffic on busy routes, this reduction could make a big difference. The transition to electric-only fleets can drastically curb one of the ocean's noisiest intrusions. It would allow all marine life to reconnect with natural sounds important for survival and prosperity.
For ferry operators and passengers alike, electric vessels deliver benefits beyond greenhouse gas reductions. No GHG means cleaner air, and less noise pollution means travellers above may better hear the ocean's wonders during crossings with more comfortable trips. As battery technology continues advancing, electric-powered ferries look poised to pave the way toward a quieter future for our seas.
This latest blog has been contributed by Luana Pandolfo, Environmental Engineer, MSc. in Water Resources and Energy Management. Luana recently completed a Master of Science from the New York Institute of Technology - Vancouver with a final project titled "Ferry Operations in Support of Marine Life". You can read that report here.
Sources
Otsason, R., & Tapaninen, U. (2023). Decarbonizing City Water Traffic: Case of Comparing Electric and Diesel-Powered Ferries. Sustainability, 15(23), 16170. https://doi.org/10.3390/su152316170
Parsons, M. J. G., Duncan, A. J., Parsons, S. K., & Erbe, C. (2020). Reducing vessel noise: An example of a solar-electric passenger ferry. The Journal of the Acoustical Society of America, 147(5), 3575–3583. https://doi.org/10.1121/10.0001264
Slabbekoorn, H., Bouton, N., van Opzeeland, I., Coers, A., ten Cate, C., & Popper, A. N. (2010). A noisy spring: the impact of globally rising underwater sound levels on fish. Trends in Ecology & Evolution, 25(7), 419–427. https://doi.org/10.1016/j.tree.2010.04.005
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