Noise emissions from ultrasonic antifouling and their potential effects on marine mammals

Biofouling on ship hulls increases drag, fuel consumption, and therefore greenhouse gas emissions. It also contributes to the spread of invasive species and can clog seawater cooling systems. Ultrasonic antifouling is an emerging technology that employs high-frequency vibrations to inhibit organism attachment, which can potentially reduce biofouling. Commercial shipping is already a major source of mostly low-frequency underwater radiated noise. The use of ultrasonic antifouling equipment raises concern whether the additional high-frequency noise emissions significantly increase the acoustic stress on marine mammals. This study evaluates the noise emissions of ultrasonic antifouling transducers installed on a tanker and a diving vessel. Underwater noise measurements and numerical propagation modeling were combined to assess the environmental side effects of the emitted underwater noise on marine mammals. The acoustical results are compared with thresholds defining the onset of a behavioral response as well as hearing impairment. It was found that sensitive species, such as harbor porpoise, can experience behavioral effects up to distances of 3 km.