Seismic Survey Risk Assessment on Common Dolphins in the South-western Coast of Portugal

While ship traffic is the primary source of anthropogenic underwater noise worldwide, locally, other sources may have a higher impact on marine life, such as seismic surveys. Although the impacts of this practice conducted in deep waters are widely investigated, less is known about the risk to biodiversity when such surveys are undertaken in shallow waters using light seismic techniques, such as for offshore wind development. The objective of this study is to assess at-risk areas by combining habitat suitability maps for the common dolphin (Delphinus delphis), selected as the target species, and noise maps from a light seismic survey simulation in the region of Setúbal (Portugal), an area of high marine biodiversity. Noise maps indicate that sound levels may reach up to 190 dB re 1μPa, impacting the species’ hearing perception in a range of approximately 40 km around the surveying zone. Habitat suitability maps showed high values in low-depth areas of the abovementioned region. Risk maps, obtained by overlapping seismic survey noise and habitat suitability maps, showed the particular sensitivity of coastal areas, especially until the bathymetric line of 250 m and higher levels of risk in a broader area in summer than in winter. The relevance of risk maps as a powerful tool for supporting environmental and marine life management policies is emphasized.