This study investigated the use of a complex quantitative simulation model for participatory geo-foresight for the governance of the marine socio-ecosystem in the Bay of Biscay. The approach is simulation-based combining qualitative and quantitative expert-knowledge focusing on the demersal fishery in the Bay of Biscay. A three-stage approach was carried out : (i) translation by stakeholders of a narrative scenario drawn up during the geo-foresight into quantitative sub-scenarios that could be parameterized in ISIS-Fish; (ii) simulation with ISIS-Fish and study of the consequences of the sub-scenarios on the dynamics of the fishery; and (iii) participants feedback on the relevance of the model, on the possibility to detail the narrative scenario further and on the general contribution of ISIS-Fish to geo-foresight. The study created discussions on input data, mechanisms and spatial features of the model and on some limits of simplistic translations of the scenario. The model and simulations highlighted the relevance of using a spatial model to explore sub-scenarios derived from geo-foresight. The flexibility of ISIS-Fish and the synergy between the quantitative modeling and scenario planning approaches allowed for demystification of complex models for fisheries management and illustrated their potential for decision-making for fisheries management.