Habitat use of Mediterranean fin whales in the recently established North-Western Mediterranean Particularly Sensitive Sea Area

The current climate change, pollution, and biodiversity crises highlight the urgent need to develop effective conservation measures for wildlife and their habitats. The Mediterranean Sea is home to some of the busiest traffic lanes globally, accounting for approximately 30% of international commercial shipping activity. These high volumes of maritime traffic pose a substantial threat to the resident, endangered sub-population of fin whales, with significant conservation and welfare concerns arising from both lethal and sub-lethal collisions and noise pollution. In 2023, the International Maritime Organization (IMO) designated a Particularly Sensitive Sea Area (PSSA) in the North-Western Mediterranean Sea, following a joint proposal from France, Italy, Monaco, and Spain. This designation acknowledges the significant adverse effects of vessel strikes on the region’s fin and sperm whales, highlighting the need for targeted conservation measures to mitigate these threats. This PSSA encompasses the existing Spanish ‘Cetacean Migration Corridor’ and the ‘Pelagos Sanctuary’, as well as the ‘North-Western Mediterranean Sea, Slope and Canyon System’ Important Marine Mammal Area (IMMA). Substantial understanding of fin whale distribution and habitat use is available for the NW Mediterranean Sea. However, knowledge of the species regional movement ecology (e.g., through the use of biologging technology), critical to support mitigation and management efforts, particularly in relation to vessel-strikes, remains limited. In this context, we assess the habitat use of endangered Mediterranean fin whales in the newly established PSSA. During four field seasons (2021–2024), 15 fin whales were equipped with satellite transmitters – including 11 SPOT and 4 Fastloc GPS tags, all in the LIMPET configuration – during their spring-summer aggregation in the Corso-Liguro-Provençal and the Balearic Basins. Hidden Markov Models (HMM) and Utilization Distributions (UD) were used to identify foraging behavior, revealing that individuals were consistent in their use of seasonal core feeding grounds, many of which occurred in areas with no explicit protected status. Based on the overlap between shipping routes and whale habitat, our research highlights how fin whales do not avoid areas of intense maritime traffic. This, alongside a potentially limited repertoire of avoidance responses to incoming traffic, makes Mediterranean fin whales particularly susceptible to collision risk. Our findings show that the recently established PSSA encompasses the entirety of the movements of the tracked fin whales across the study period, except for one individual who left the study area. These findings underscore the need for a mandatory vessel speed reduction rule to 10-13 knots to be adopted among the Associated Protective Measures (APM), in addition to other recommended voluntary measures already in place within the PSSA.