The objective of this paper is to develop and evaluate a micro-economical microworld which will allow policy makers to gain more insight in parameters that influence the Belgian fishery fleet structure. In a later stage, this microworld may contribute to the process of developing a long-term strategy for the Belgian fishery sector, serving as a laboratory for ex-ante evaluation of possible strategies. (Keys, Fulmer, and Stumpf 1996; De Geus 1997) By visualizing decisions and strategies (Morecroft 1999), it generates insights about fleet dynamics in response to a changing environment and policy changes.