Green sea turtles (Chelonia mydas) inhabit tropical and subtropical oceans worldwide. Living in the marine environment and laying eggs on the beach, they are mainly threatened by human activities (poaching, fisheries bycatch, habitat destruction, etc.). In Reunion Island, the Kélonia observatory and IFREMER develop various scientific programs to study and protect sea turtles. One of them consists in studying migrations of green sea turtles for mating purpose. As existing mathematical models struggle to take spatial dimension into account, we propose an agent-based model to study some of the numerous questions regarding green sea turtles migrations. Coming with high expectations, experts in sea turtles also provide many heterogeneous but incomplete data. Considering available or obtainable data in one hand and the various questions of experts in the other hand, we defined an innovative modelling process in which we simultaneously conduct discussion with experts and prototyping. This paper aims at presenting our simulation model but also our approach as well as the data-collection and modelling roadmap it produced.