Common dolphin's shipping noise risk assessment on the Portuguese coast.

Ocean noise generated by human activities at sea has been increasing over the decades, affecting marine ecosystems. Ship traffic flow between the Mediterranean or South Atlantic and northern Europe makes the coast of Portugal one of the most intense shipping highways on a global scale. Among the cetaceans of the coast of Portugal, the common dolphin (Delphinus delphis) was selected as a target species. Based on 15 years of observations, the common dolphins' habitat suitability was estimated, together with the shipping noise maps for the year 2019, to produce seasonal risk maps for the same year. A large number of areas with a high noise risk index (≥0.85) were found in Portugal's southern and southwestern coasts, especially during the summer and fall seasons. Comparably, the 0.50 risk index exceeds 7 % and 3.5 % of the total area in summer and fall, respectively. These percentages decrease to 1 % in spring and winter.