Quantifying effects of fishing on marine trophic webs

Exploited ecosystems are characterised by exports of secondary production from each fished trophic level that reduce the energy available for upper levels at ecosystem scale thus impinging on overall secondary productions. Depletion in secondary production with respect to the unfished state is here proposed as a proxy for quantifying ecosystem effects of fishing. Theoretical analysis of trophic web interactions permit quantifying the ‘Loss in production’ and provides ecological basis for defining a new synthetic index (L index), which takes into account both ecosystem properties (Primary Production and Transfer Efficiency) and features of fishing activities (Trophic Level of catches and Primary Production Required). Quantitative meta-analysis of ecological models, representing 51 exploited ecosystems previously classified as overexploited or sustainably exploited, allows associating to each index value a probability of the ecosystem being sustainably fished. Moreover, by fixing the reference level for this probability, the index provides basis for estimating the maximum allowable catches. L index is here applied to several ecosystems worldwide using landing data and ecological models, * Corresponding author: Simone Libralato, Email: [email protected]