- Underwater anthropogenic sound levels in the ocean are increasing, and the evidence for impacts of sound on marine life is overwhelming. Currently, regulatory bodies require emitted sound from marine renewable energy projects to be assessed in order to infer potential impacts on marine life. Geometric spreading models are sometimes used to assess likely ecological impacts of anthropogenic sound by estimating the propagation of underwater sound without in situ verification.
- This study investigated the propagation of anthropogenic sound in shallow waters (25–45 m deep) from a single monopole (a single loudspeaker) and twin monopole (two loudspeakers) sound sources replaying tidal turbine sound to approximate anthropogenic sound sources in this environment.
- Greater sound levels at 100–800, 801–2000 and 2001–20 000 Hz were observed at all observation distances from the sound source for the twin monopole compared to the single monopole. These results suggest that the sound from multiple anthropogenic sound sources installed in one location is likely to be cumulative in the environment where their sound fields overlap.
- Sound intensities observed in both the single monopole and twin monopole experiments for 0·1–20 kHz were higher than estimates derived from standard geometric spreading models for underwater sound by 3–41 dB across all measured distances from the source. The greatest difference from the theoretical spherical spreading model (41 dB) occurred at the site most distant from the twin monopole sound source, that is, 5 km.
- Synthesis and applications. The results show that geometric models used by some regulatory bodies may be underestimating the spatial extent to which the anthropogenic underwater sound may be propagating and creating potential ecological impacts. Based on field measurements, we have presented an alternative model which should assist regulatory agencies to better estimate and manage ecological impacts from anthropogenic underwater sound.