Fishing impact in Mediterranean ecosystems: an EcoTroph modeling approach

Institut de Recherche pour le Developpement (IRD); project BISTROMED (ENVI-Med - MISTRALS); project CHARMMED (Fondation TOTAL); Marie Curie CIG grant [PCIG10-GA-2011-303534]; Spanish Research Program Ramon y Cajal; FP7 project PERSEUS (FP7 Theme "Oceans of Tomorrow" OCEAN) [287600]This publication has been produced with the financial support of the DPF PhD fellowships program of the Institut de Recherche pour le Developpement (IRD) for GH and TH. It was also partly funded by the projects BISTROMED (ENVI-Med - MISTRALS) and CHARMMED (Fondation TOTAL). MC was partially supported by a Marie Curie CIG grant (PCIG10-GA-2011-303534) to the BIOWEB project and the Spanish Research Program Ramon y Cajal. KT was partially supported by the FP7 project PERSEUS (FP7 Theme "Oceans of Tomorrow" OCEAN.2011-3 Grant Agreement No. 287600).

English. The EcoTroph modeling approach was applied to five Mediterranean marine ecosystems to characterize their food webs and investigate their responses to several simulated fishing scenarios. First, EcoTroph was used to synthesize the outputs of five pre-existing heterogeneous Ecopath models in a common framework, and thus to compare different ecosystems through their trophic spectra of biomass, catch, and fishing mortalities. This approach contributes to our understanding of ecosystem functioning, from both ecological and fisheries perspectives. Then, we assessed the sensitivity of each ecosystem to fishery, using EcoTroph simulations. For the five ecosystems considered, we simulated the effects of increasing or decreasing fishing mortalities on both the biomass and the catch per trophic class. Our results emphasize that the Mediterranean Sea is strongly affected by the depletion of high trophic level organisms. Results also show that fisheries impacts, at the trophic level scale, differ between ecosystems according to their trophic structure and exploitation patterns. A top-down compensation effect is observed in some simulations where a fishing-induced decrease in the biomass of predators impacts their prey, leading to an increase in the biomass at lower trophic levels. The results of this comparative analysis highlight that ecosystems where top-down controls are observed are less sensitive to variations in fishing mortality in terms of total ecosystem biomass. This suggests that the magnitude of top-down control present in a system can affect its stability.