An ecosystem model as a basis for the holistic approach to fisheries in the Strait of Sicily

The central position in the Mediterranean Sea and the impressive biological diversity, productivity and habitat heterogeneity found there makes the Straits of Sicily an important fishing ground for the whole basin. In the Straits several target fish species are exploited by one of the largest Mediterranean fisheries. Despite the economic and ecological importance of the area an in-depth study of the interaction between species and gears as a whole for the sustainable use of the marine resources is still lacking. A holistic ecosystem model has been developed for the ecological and bio-economical analysis of the fisheries in the area. The applied ECOPATH model included the reconstruction of the Straits of Sicily food web which includes 72 functional groups, from bacteria to large pelagic species. Important commercial species were treated as single groups, including the red mullet and the European hake represented in age classes. In order to better represent main ecological and exploitation differences, many functional groups were split into shelf and slope components. Fishery was described by 39 fleet segments resulting from combination of 13 métiers and 3 fishing vessel size. Results showed ontogenetic diet shifts for red mullet and European hake; moreover, large hakes were at the top of food web. Red mullet, European hake, deep water rose shrimp, giant red shrimp and clupeids represent the bulk of catches (more than 60%) and as a consequence mean trophic level of catches resulted about 3.5. Although trawlers highly impacted the system, functional groups remained largely interconnected as suggested by the system omnivores index (SOI=0.34). Furthermore, the Straits of Sicily appeared at an intermediate stage of maturity (Tot PP/Tot R=1.71) compared to other Mediterranean regions. The approach followed in this study allowed to identify interactions between fleet segments as well as species with key ecological role for ecosystem resilience. The model developed permitted a first ecosystem evaluation of fishing effects in the Straits of Sicily and a basis for testing management scenarios.