Roberto Crosti

Seasonal characterisation of maritime traffic and the relationship with cetacean presence in the Western Mediterranean Sea

Seasonal maritime traffic was investigated in relation to cetaceans, through direct observations (July 2013-June 2015) along three fixed transects in Western Mediterranean. Visually obtained vessel abundance was compared with Automatic Identification System data to explore if the two methods provided different results. Traffic intensity and composition were characterised by seasons and vessel categories. Finally, cetacean presence was investigated in relation to traffic by measuring the difference of vessel abundance in the presence and absence of animal sightings. Results showed that visual sampling was consistent with AIS data, providing more information on small-medium vessels. Traffic was more intense and diverse in Spring/Summer, and the highest vessel abundance and seasonal variations in composition emerged for inshore subareas. The difference of traffic in the presence and absence of cetaceans was higher in most offshore subareas in Spring/Summer, verified for B. physalus and S. coeruleoalba; in inshore waters, mostly occupied by T. truncatus, no significant differences emerged.

Amount, composition, and spatial distribution of floating macro litter along fixed trans-border transects in the Mediterranean basin

Marine litter is a major source of pollution in the Mediterranean basin, but despite legislative requirements, scant information is available for the ongoing assessment of this threat. Using higher size classes as proxy for litter distribution, this study gave a synoptic estimation of the amount, composition, and distribution of floating macro-litter in the Mediterranean. The average amount of macro-litter was in a range of 2-5items/km2, with the highest in the Adriatic basin. Seasonal patterns were present in almost all study areas and were significant in the Ligurian Sea, Sardinian-Balearic basin, and Central Tyrrhenian Sea. Plastic accounted for >80% of litter in all areas and seasons, with the highest proportion in the Adriatic Sea, Ligurian Sea, and Sicilian-Sardinian Channels; in the Bonifacio Strait, Tyrrhenian Sea, and Sardinian-Balearic basin, litter composition was instead more diverse. Spatial analysis suggested an almost homogeneous distribution of litter without evident regular aggregation zones.

Seasonal patterns of floating macro-litter across the Western Mediterranean Sea: a potential threat for cetacean species

Marine litter is a major form of pollution in the Mediterranean, but despite legislative requirements, additional information is still needed to evaluate basin-scale amounts, trends, and potential threats for the biota, especially for Habitats Directive listed species, such as cetaceans. Through repeated sampling of floating macro-litter along a fixed transect between Spain and Italy, this study provided detailed data within four marine sectors of the Western Mediterranean Sea, characterized by seasonal variability in oceanographic/ecological conditions and anthropogenic pressure. Moreover, we identified the areas of major overlap between high density of plastic and cetacean sightings. Litter was composed of plastic for more than 65%, with more diverse compositions occurring in the Balearic and Sardinian Sea compared to the semi-enclosed Bonifacio and Tyrrhenian sectors. The average amount of macro-litter ranged between 1.9 and 2.8 items km−2 and reached the highest values in spring/summer in all basins, suggesting a relationship with the increasing of touristic and maritime activities, both in coastal and offshore waters. The Balearic and Bonifacio sectors showed higher amounts and larger accumulation areas for plastic, likely due to a combination of multiple sources and oceanographic processes influencing the distributional patterns. Cetacean sightings were recorded in all sectors with fin whale (Balaenoptera physalus) and striped dolphin (Stenella coeruleoalba) as the most frequent species. The presence of cetaceans in areas with high densities of plastic emerged mostly during spring/summer in the Balearic and Bonifacio sectors, but other specific areas of potential exposure were identified, indicating the need for a dynamic definition of this threat.