The impact of marine traffic radiated underwater noise on the in the Baltic Sea

Continuous anthropogenic noise, generated by commercial shipping, is considered to exert a considerable pressure on the marine environment. Noise emitted by ships is mainly due to their propellers whose energy is predominantly at low frequencies and can interfere with the communication of marine animals. The EU Marine Strategy Framework Directive (MSFD), has set the objective of achieving good environmental status of Europe's seas. In particular, anthropogenic underwater sound should be at a level that does not harm the marine environment. Here we present the first implementation of the new framework for assessing the environmental status of low frequency continuous noise on a basin scale, carried out in the frames of the EU-funded HELCOM BLUES project. The assessment was based on modeled levels in two 125 and 500 Hz decidecade bands deemed relevant for the indicator fish and marine mammals respectively. Sound propagation modelling, calibrated against underwater ambient noise monitoring data, results in statistical sound maps in species-specific frequency bands. The application of spatial thresholds allows the environmental status of marine areas to be determined. Factors affecting the reliability of results are discussed.