International agreements require fisheries policy to be based on an ecosystem approach. The overall objective of this project is to achieve a better understanding of marine ecosystem management with a combination of ecological criteria (keeping all specie s, including those that compete with humans for the same fish, above some minimum level) andeconomical criteria (e.g., maximising profit). We will obtain this by making a bio-economic model which takes into account the effect of fisheries, the effect of species interactions, andthe effect of climatic variations (and possibly trends). We will focus on plankton-feeding fish and seabirds in the Barents Sea andthe Benguela System within a comparative setting.