Measurements of radiated underwater noise from modern merchant ships relevant to noise impacts on marine mammals.

Abstract

There is mounting concern over the effect of ship noise on marine mammals; however, limited empirical data quantifying this noise impede our ability to evaluate impacts. An opportunistic approach for measuring radiated ship noise (20–1000 Hz) was used in this study. Calibrated acoustic data were combined with archived information on seven types of modern merchant ships transiting the coast of southern California. Three metrics for describing ship noise were applied: received sound levels (RLs) during 1 h passages, estimated source levels (SLs), and sound exposure levels (SELs). 1 h passages provided an estimate of the spatial extent of ship noise. At 40 Hz, container ships elevated noise above background up to 7 km forward of the ship and 19 km aft; bulk carriers elevated noise above background up to 5 km at bow and stern aspects. These ship‐types had similar broad band estimated SL, 186 dB re 1 μPa at 1 m. The cumulative exposure to ship noise varied by ship type; we presented equations for estimating SELs for specific ship types. In concert, these metrics create a tool for quantifying ship noise within coastal marine environments, and can be used to assess the impact of ship noise on marine mammals. [This work was supported by the U.S. Navy CNO N45 and additional funds from the ONR, the NOAA, and the NSF.]