In this study, hydroacoustic data collected with a scientific echosounder working at two frequencies (38 and 120 kHz) over the continental shelf off the southern Sicilian coast were used in order to investigate the relationship between fish schools and plankton patches. Specifically, image analysis algorithms were applied to raw echograms in order to detect and characterise pelagic fish schools and plankton aggregations, considered as a proxy of food availability. The relationship was first investigated using estimated total plankton biomass over the whole water column and, second, by dividing the study area into three sub-regions and further distinguishing plankton patches between the surface and the bottom. In the relatively lower plankton abundance areas of Zone 1 (northern sector of the study area), results showed an inverse relationship between the biomass (and density) of fish schools and the biomass of co-occurring plankton patches located close to the bottom. Instead, over the Sicilian-Maltese shelf (Zone 3), characterised by higher plankton abundances, a direct relationship was found when using plankton data from the whole water column. The observed difference between Zones 1 and 3 is probably due to diverse dominant fish species in the two sub-regions.

Understanding recent thermohaline variability is essential to assess ongoing changes in circulation and water-mass properties in the western Mediterranean Sea. This study investigates the spatial and interannual evolution of surface and intermediate water masses along the Ligurian and Tyrrhenian continental shelves utilizing a unique dataset of twelve summer CTD surveys collected between 2009 and 2022 as part of the EVATIR programme. In situ observations are complemented by satellite-derived sea surface temperature, atmospheric forcing data, and three-dimensional ocean reanalysis products to contextualize the observed variability within a coherent physical framework.The CTD data reveal a transition from a relatively cold–fresh regime toward a warmer and more saline state affecting both the surface and intermediate layers of the southern Tyrrhenian shelf. In this sector, Atlantic Water shows clear decadal-scale changes, marked by increasing salinity at its core and a significant warming at the salinity minimum (approximately +0.23 ◦C yr−1).Similar changes are observed within the intermediate layer (90–200 m), which exhibits a statistically significant long-term warming accompanied by increasing salinity, indicating that the thermohaline transition extends throughout the upper water column. By contrast, the central Tyrrhenian and Ligurian shelves do not display statistically significant long-term trends, with interannual variability remaining the dominant signal.The observed thermohaline evolution is closely associated with changes in winter surface conditions. February sea surface temperature fields show a marked contraction of cold winter signatures after 2013, suggesting a reduction in the spatial extent and intensity of winter surface cooling. Consistently, the analysis of atmospheric forcing and air–sea heat fluxes reveals weaker northerly winds and decreased winter buoyancy loss in recent years, conditions that are less favourable for deep winter mixing and the ventilation of ransitional intermediate waters. Additional dynamical support is provided by three-dimensional Copernicus Marine reanalysis fields, which indicate a progressive shoaling of winter mixing and a reduced penetration of cold waters into intermediate depths within the Bonifacio Cyclonic Gyre. Overall, the results document a regime transition in water-mass properties along the western Italian shelf and emphasise the sensitivity of shelf hydrography to changes in winter atmospheric forcing.