Year-round acoustic patterns of dolphins and interaction with anthropogenic activities in the Sicily Strait, central Mediterranean Sea

Understanding spatio-temporal patterns of top predators can be crucial for evaluating key habitats, assessing the effects of anthropogenic activity and consequently applying suitable management policies. Here, we characterized dolphins acoustic occurrence and interactions with boat presence and noise in the waters of the Sicily Strait. A hydrophone was deployed on an elastic beacon three miles off the coast of south-west Sicily, and recorded continuously for 14 months, from January 2015. Results revealed that packed and train clicks types were the most detected signals, suggesting that animals were especially involved in feeding activity. A regular year-round acoustic presence was recorded, with seasonal variability. Two peaks were detected during the year in August and November, cuncurrently with a possible increase in fish biomass in the area. An abrupt decrease in click detection rate in September coincides with the biological shutdown in 2015 and the shift of fishing vessels offshore, suggesting a possible movement of dolphins following trawlers. Furthermore, dolphins vocalized more during the night-time, probably carrying out movements to and from the coast. Results indicated that dolphins interact with trawlers during mid-morning when an intermediate level of activity was collected, but click detection rate decreased with increasing noise levels at one-third octave bands centered at 250 Hz. Outcomes can help inform conservation efforts and the development of monitoring programmes focused on environmental impact assessments under the EU Marine Strategy Framework Directive.