Motorboat sound in shallow waters and implications for mitigation

Small motorboats are a pervasive source of underwater noise pollution in many coastal regions of the world. The environmental impacts of motorboat noise include marine life disturbances and ecosystem disruptions. Mitigation strategies may involve speed restrictions in certain areas, on the assumption that slower speeds correspond to lower acoustic energy. We investigate the acoustic footprint of small motorboats navigating at different speeds in shallow water. Sound pressure and particle motion are characterized and the source levels estimated. We find that the acoustic energy (source level) associated with small motorboat noise may be higher at low speed than high speed. Our study therefore suggests that the vessel's optimal cruising speed should be considered while implementing speed limitation as a mitigation strategy.