Record of South American sea lion (Otaria byronia) stranding reports on the Peruvian coast (2017–2023): implications for conservation of the species

Marine mammal strandings are an important source of information for assessing the condition of marine ecosystems and the influence of environmental, sanitary and anthropogenic factors. The pinniped species most commonly involved in stranding events in Peru is Otaria byronia. In this study, we analyzed reports of Otaria byronia strandings recorded by the Alerta SERFOR (National Forest and Wildlife Service) program between 2017 and 2023, in order to identify temporal patterns and their relationship with the Coastal El Niño Index (ICEN), monthly Peruvian anchoveta (Engraulis ringens) landings, and the occurrence of the avian influenza A H5N1 epizootic. Our analysis revealed a progressive increase in the frequency of stranding reports, beginning in 2021 and peaking at 2199 stranded individuals recorded in 2023. A statistically significant association was identified between the frequency of stranding reports and the ICEN, as well as between stranding reports and the presence of the avian influenza A H5N1 epizootic. In contrast, no statistically significant relationship was found between stranding reports and monthly Peruvian anchoveta landings. These results highlight the association between oceanographic anomalies and sanitary events, shed light on the dynamics of stranding reports, and emphasize the importance of strengthening monitoring systems for the conservation of the species along the Peruvian coast.