Fin Whale (Balaenoptera physalus) Mortality along the Italian Coast between 1624 and 2021

SIMPLE SUMMARY: We present a comprehensive overview of fin whale historical and modern mortality events that occurred between 1624 and 2021 along the Italian coast, highlighting spatial and temporal patterns and, where possible, the proximal causes of mortality. Emerging hot spot analysis shows the spatial and temporal consistency of mortality events along the northern coast of the island of Sardinia, the central coast of Tuscany and the Gulf of Trieste in the northern Adriatic Sea. The coast of Liguria and the northern coast of Tuscany are sporadic hot spots, while the central coast of Italy along the Tyrrhenian Sea as well as the coast of southern Sardinia and northern Sicily have been identified as new hot spots of mortality events for the species. While the analysis of the temporal patterns suggests a steep increase in the number of mortality events starting in the second half of the 1980s, we cannot exclude the possibility that this positive trend is the result of a strong observer bias. Conversely, recent mortality events seem to be consistent in number over the last six decades and subject to year-round seasonality. Our results show that younger and immature individuals are the fin whales most affected by ship strikes. This study supports the implementation of a conservation plan to ensure the survival of the species in the Mediterranean region. ABSTRACT: The Mediterranean Sea hosts a population of fin whale (Balaenoptera physalus), the only species of Mysticete regularly occurring in the basin. Observed and inferred mortality suggests that the population is likely declining. Accordingly, understanding the causes of mortality and assessing the health status is pivotal to the survival of this endangered population. While such studies are inherently difficult for a highly roaming species with a pelagic distribution, mortality events provide the opportunity to investigate biological and epidemiological traits linked to these events, and evaluate the footprint of human activity, especially when long-term data series exist. We present a comprehensive spatial–temporal overview of fin whale mortality events along the Italian coast encompassing four centuries (1624–2021). Time series analysis was used to highlight structural changes in the evolution of mortality through time, while spatial–temporal patterns in the distribution of mortality events were assessed through emerging hot spot analysis methods. Recent mortality events (1964–2021) were further explored to evaluate, where possible, the primary causes of mortality and to identify anthropogenic threats of conservation concerns. This long-term survey offers the basis for an understanding of the health status of this B. physalus population and provides much-needed information for developing an effective management and conservation plan for the species in the region.