Sound Maps Of The Dutch North Sea For Natural And Anthropogenic Sound Sources

Regulations for protecting and preserving the marine environment (e.g. in the USA and EU) often require investigating the potential effect of anthropogenic sound on marine life. The origin of underwater sound can be natural as well as anthropogenic. To assess the potential importance of various types of sounds, we constructed sound maps for the Dutch North Sea for both natural sources (i.e. wind and rain) and anthropogenic sources (shipping, explosions, and seismic surveys). Different sources affect different species, because of different frequency ranges or because of their distribution in time (e.g., continuous or intermittent; changing suddenly or gradually). Our maps take into account different averaging times, different swimming depths and frequency-weighting according to different hearing sensitivities. The underwater acoustic propagation is modeled mathematically by combining Weston’s average intensity method and adiabatic normal mode theory, which can provide fast and accurate results without calculation of normal mode eigenvalues and tracing rays. These maps, combined with information on species distribution and their physiological and behavioural reactions to sound, provide a useful indicator for understanding the impact of sound on marine life in the Dutch part of North Sea.