Acoustically detected pelagic fish community in relation to environmental conditions observed in the Central Mediterranean sea: a comparison of Libyan and Sicilian-Maltese coastal areas

摘要

An analysis of the influence of environmental conditions on the pelagic fish community structure and species distribution in two areas of the Central Mediterranean sea, the Sicilian-Maltese and the Libyan continental shelves, is presented. The Libyan waters suffer from the lack of historical information on these species, and a thorough characterisation of the pelagic fish community is missing for the entire study area. In summer 2008, two multidisciplinary surveys permitted for the first time the collection of acoustic, biological, and hydrological data in the Libyan, Maltese, and Italian waters of the Central Mediterranean. Satellite and in situ measurements were used here to describe the environmental conditions characterising the two ecosystems, and to analyse the relationships between environmental factors and pelagic community structure, and pelagic fish biomass. The datasets support the hypothesis of a more favourable feeding ground for pelagic fishes in the southwestern part of the study area, close to the Gulf of Gabes, characterised by a larger continental shelf and a higher productivity than the northern and the eastern sides. Environmental gradients, such as the ones related to temperature and salinity, may influence in different ways the pelagic fish community structure in the two areas. The Libyan waters, where environmental gradients develop longitudinally in about 700 nmi, likely produce a better spatially structured fish community. In the Sicilian-Maltese area, characterised by stronger environmental gradients and shorter longitudinal extension (150 nmi), such spatial structure is less evident. In this latter area a higher spatial overlap among pelagic species is mainly linked to the limited continental shelf and the spatially compressed environmental gradients.