The impact on marine mammals of underwater radiated noise (URN) from vessel traffic is under active international study and of increasing concern. The focus has been on “passive” URN from machinery, hull, propulsion, and flow noise. Active acoustic radiation from echolocation devices has received little attention, although these devices are pervasive, mandated for a wide range of vessels and contribute significantly to the overall URN signature within the most sensitive portions of the hearing ranges of some threatened whale species.
It is concluded that a highly effective mitigation measure, in step with market trends, would be a move from traditional low frequency devices to 200+ kHz operation with broadband (chirp, typically) waveforms, a high degree of power control and the ability to temporarily deactivate lower frequency channels in the case of multi-frequency devices. The most rapid benefits can be achieved by encouraging this in the unregulated sector comprising recreational vessels and vessels with displacement less than 150 GT. The regulated sector above 150 GT can also benefit over a longer time scale, due primarily to type-approval requirements and associated schedules and costs.
Recommendations are provided for a way ahead, including a program of further interaction with manufacturers and users to highlight these issues and further develop the operational and technical solutions in a manner that is quickly and easily deployed across all fleets.