Ecosystem Viable Yields
This work addresses the gap between ecosystem-based management and current fisheries practices by introducing a robust, non-equilibrium yield concept for multispecies fisheries.
The authors propose a definition of 'ecosystem viable yields' (EVY) that ensures biological safety and ecosystem dynamics, contrasting with the single-species maximum sustainable yield (MSY). They provide explicit EVY expressions for multispecies models and apply them to the anchovy-hake system in Peru.
The World Summit on Sustainable Development (Johannesburg, 2002) encouraged the application of the ecosystem approach by 2010. However, at the same Summit, the signatory States undertook to restore and exploit their stocks at maximum sustainable yield (MSY), a concept and practice without ecosystemic dimension, since MSY is computed species by species, on the basis of a monospecific model. Acknowledging this gap, we propose a definition of "ecosystem viable yields" (EVY) as yields compatible i) with guaranteed biological safety levels for all time and ii) with an ecosystem dynamics. To the difference of MSY, this notion is not based on equilibrium, but on viability theory, which offers advantages for robustness. For a generic class of multispecies models with harvesting, we provide explicit expressions for the EVY. We apply our approach to the anchovy--hake couple in the Peruvian upwelling ecosystem.