Anthropic pressure on cetaceans stranded along the Ligurian coast within the Pelagos Sanctuary

Marine mammals are extremely sensitive to the disturbance of ecosystems due to human activities. In this study, data collected by the Italian National Reference Center for Diagnosis of stranded Marine Mammals over a 3-year period (2020 – 2022), were considered to assess the anthropic pressure on cetaceans living in the Ligurian sea. Out of a total of 37 stranded cetaceans within the concerned period and area, a complete post-mortem examination was performed on 23 cases. Of these, 14 were further selected considering at least one of these conditions: confirmed or probable interaction with fishing activities through the application of a standardized diagnostic framework (7/14=50%); toxicological stress through the evaluation of organochlorine compounds (OCs) hazardous levels (PCBs, HCBs, DDTs) (13/14=93%) and terrestrial pathogens-associated disease (systemic infection and/or associated lesions) (7/14=50%). Based on gross and microscopic pathology and ancillary testing, hypotheses on the cause of death were formulated for 9/14 animals. In 6/14 cases the cause of death was associated with natural origin, specifically represented by infectious diseases due to terrestrial pathogens in 4/5 cases. In 3/14 cases the cause of death was categorized as anthropic due to fishery interaction, specifically represented by bycatch with active fishing gear as a consequence of underlying pathologies, related to terrestrial pathogens in 2/3 cases. The cause of death was not determined in 5/14 cases. Among them, 2/5 cases showed evidence of suspected fishing interaction (bycatch with not determined fishing gear) and 1/5 showed Toxoplasma gondii and Erysipelothrix rhusiopathiae systemic infection together with fishing gear agglomerate ingestion. Furthermore, marine debris ingestion was assessed through a standardized method, confirming the presence of macro, meso and microplastics in 6/14 cases. These data are important evidence of the anthropogenic pressure to which cetaceans in the Pelagos Sanctuary are subjected to, which is affecting both individuals health and population conservation status.