Trends in cetacean presence in the Pelagos Sanctuary

Several National and international legislative frameworks have recognized cetaceans as suitable indicators of ecosystem health. For the MSFD, trends in cetacean presence and distribution are used to evaluate the Good Environmental Status. In this work data collected within FLT Med Network from 2008 to 2023 along different fixed transects crossing the Ligurian Sea has been used, to evaluate cetacean presence trends in the offshore areas of the Pelagos Sanctuary. Applying the methodology developed in Tepsich et al. (2020), a strip-transect analysis framework has been established and density index for four cetacean species encountered have been computed, for the three reporting periods (2008-2012; 2013-2018; 2019-2023). Anomalous years have also been identified. Overall, 860 surveys have been performed accounting for over 5000 cetacean sightings. Results show a strong interannual variability for fin whales, striped dolphins and goose-beaked whales, while sperm whale presence has been rather constant along the survey period. Fin whales showed an increasing trend from 2008 to 2012, followed by a stable trend and a further increasing trend over the last period. For striped dolphins and sperm whales the general trend was found to be stable over the three periods, while goose-beaked whales are the only species showing a constant positive trend. Anomalous years have also been identified, specifically negative years were 2009 and 2014 for fin whales (2014 density index=0.03 and 2009 DI = 0.08 versus a mean DI=0.34) and 2016 (2016 DI=0.7 versus a mean DI=1.4) for striped dolphins, while 2023 has been an anomalous positive year for fin whales (DI=0.8). No anomaly has been identified for sperm whales. Our results confirmed the effectiveness of the methodology for assessment of trends of species presence in offshore areas, highlighting the importance of a yearly monitoring program.