This paper illustrates an improvement of the IREPA 'Moses' bio-economic model for the optimal management of fishing effort. A description of the model procedure for the optimal allocation of fishing effort and some results are reported. In order to assess the reallocation of labour units between areas and gears, an up-grading formulation of the concepts of inertia term and reconversion cost is introduced. Scope of this paper is the formulation of a linear programming problem that minimises the total reconversion cost of effort variations resulting from the optimisation analysis. Summary of the procedure is exposed, together with results applied to trawling and multipurpose fleet segments, combined. A brief discussion of results is also reported.