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The Mediterranean Sea is a high‐density maritime traffic area, particularly in the Pelagos Sanctuary. Ship strikes pose a substantial threat to fin whales (Balaenoptera physalus) according to reports from the IUCN, the IWC, the ACCOBAMS and the EU Habitats Directive. Near miss events (NMEs) were collected, as a proxy indicator of ship strikes for fin whales, along the main ferry routes crossing the Pelagos Sanctuary and adjacent western waters during ‘summertime’ (April to October). The ‘Fixed Line Transect Med Network’ carries out systematic surveys from ferries and collects data according to the ‘linear transect’ method. From 2008 to 2019, 13 different ferry routes were surveyed with 238,499 km monitored. Of the 2,775 fin whales encountered, 43 individuals were involved in NMEs (1.55% of the sightings). NMEs occur over the great majority of the routes monitored with enough effort and were correlated with the density index of fin whales. High‐risk areas for NMEs were identified in the central and deeper parts of the north‐western Mediterranean Sea and in some sections of the northern Tyrrhenian Sea. Of all NMEs, the majority of whales (63.4%) surfaced in front of the vessel (<50 m), leaving no time for the crew to manoeuvre the vessel. The others were travelling (26.8%) or resting (9.7%) without any noticeable reaction at the vessel. The speed of the ferries seems to play a role in the occurrence of the NME, as this parameter is significantly different (t‐test, P = 0.002) for NMEs compared to all fin whale sightings, whereas month and hour of day were not. Quantifying NMEs based on real‐time observation with observers on board, could be used as a feasible and efficient way to limit collisions, raising awareness by the crew, and testing or evaluating other potential tools that can help mitigate this threat.

IntroductionConservation of cetaceans is challenging due to their large-range, highly-dynamic nature. The EU Habitats Directive (HD) reports 78% of species in ‘unknown’ conservation status, and information on low-density/elusive species such G.griseus, G.melas, Z.cavirostris is the most scattered.MethodsThe FLT-Net programme has regularly collected year-round data along trans-border fixed-transects in the Mediterranean Sea since 2007. Nearly 7,500 cetacean sightings were recorded over 500,000 km of effort with 296 of less-common species. Comparing data across two HD 6-years periods (2013-2019/2008-2012), this study aimed at testing four potential indicators to assess range and habitat short-term trends of G.griseus, G.melas, Z.cavirostris: 1) change in Observed Distributional Range-ODR based on known occurrence, calculated through the Kernel smoother within the effort area; 2) change in Ecological Potential Range-EPR extent, predicted through Spatial Distribution Models; 3) Range Pattern, assessed as overlap and shift of core areas between periods; 4) changes in ODR vs EPR.ResultsMost ODR and EPR confirmed the persistence of known important sites, especially in the Western-Mediterranean. All species, however, exhibit changes in the distribution extent (contraction or expansion) and an offshore shift, possibly indicating exploitation of new areas or avoidance of more impacted ones.DiscussionResults confirmed that the ODR could underestimate the real occupied range, as referring to the effort area only; it can be used to detect trends providing that the spatio-temporal effort scale is representative of species range. The EPR allows generalising species distribution outside the effort area, defining species’ Habitat and the Occupied/Potential Range proportion. To investigate range-trends, EPR needs to be adjusted based also on the Occupied/Potential Range proportion since it could be larger than the occupied range in presence of limiting factors, or smaller, if anthropogenic pressures force the species outside the ecological niche.ConclusionUsing complementary indicators proved valuable to evaluate the significance of changes. The concurrent analysis of more species with similar ecology was also critical to assess whether the detected changes are species-specific or representative of broader trends. The FLT-Net sampling strategy proved adequate for trend assessment in the Western-Mediterranean and Adriatic basins, while more transects are needed to characterize the Central-Mediterranean and Aegean-Levantine ecological variability.

Background The Mediterranean subpopulation of fin whale Balaenoptera physalus (Linnaeus, 1758) has recently been listed as Vulnerable by the IUCN Red List of threatened species. The species is also listed as species in need of strict protection under the Habitat Directive and is one of the indicators for the assessment of Good Environmental Status under the MSFD. Reference values on population abundance and trends are needed in order to set the threshold values and to assess the conservation status of the population. Methods Yearly summer monitoring using ferries as platform of opportunity was performed since 2008 within the framework of the FLT Med Network. Data were collected along several fixed transects crossing the Western Mediterranean basin and the Adriatic and Ionian region. Species presence, expressed by density recorded along the sampled transects, was inspected for assessing interannual variability together with group size. Generalized Additive Models were used to describe density trends over a 11 years’ period (2008–2018). A spatial multi-scale approach was used to highlight intra-basin differences in species presence and distribution during the years. Results Summer presence of fin whales in the western Mediterranean area showed a strong interannual variability, characterized by the alternance of rich and poor years. Small and large groups of fin whales were sighted only during rich years, confirming the favorable feeding condition influencing species presence. Trends highlighted by the GAM can be summarized as positive from 2008 to 2013, and slightly negative from 2014 to 2018. The sub-areas analysis showed a similar pattern, but with a more stable trend during the second period in the Pelagos Sanctuary sub-area, and a negative one in the other two sub-areas. Our findings further confirm the need for an integrated approach foreseeing both, large scale surveys and yearly monitoring at different spatial scales to correct and interpret the basin wide abundance estimates, and to correlate spatial and temporal trends with the ecological and anthropogenic drivers.