Network effects in multi-species fisheries.

Managing sustainable marine fisheries is one of the greatest challenges for humanity. The complexity of the issue calls for the development of socio-ecological models and the integration of our knowledge from several disciplines. Here we focus on the ecological aspects of sustainability: how can we increase the catch and, at the same time, possibly decrease negative effects on the marine ecosystem. Coexisting species live in richly interconnected interaction networks. This means that changes in their biomass are caused and may cause various direct and indirect effects on all other coexisting species in the food web. The assessment of maximum sustainable yield values is typically based on single-species analyses, poorly considering this multi-species context. If several fish species are exploited in particular combinations, their effects may not be additive and non-additivity may mean dampening. In these cases, the community response to fishing species A and B together may be smaller than the sum of fishing species A and B separately. We report on some preliminary results on how to develop a network algebra framework for better understanding food web simulation results for pairwise perturbations and their counter-intuitive effects.