Macro analytical models - surplus production - Winter School on Towards Ecosystem Based Management of Marine Fisheries – Building Mass Balance Trophic and Simulation Models

Surplus production models are an important approach to the study of harvested populations’ dynamics. Such models are based on quite simple equations where both the state of the population and fishing activity are each described by a single variable. These models take into account only the interrelationship between observable inputs such as fishing effort and observable output which is the yield obtained from the fishery. In surplus production models the stock is considered as a single unit of biomass and modeling is not based on any age structure, length structure or dynamics of the population in terms of growth and mortalities. Instead, in these models the entire stock, the fishing effort and the total yield obtained from the stock are studied and a relationship between these are established without considering any micro level details such as growth, mortality, age at first capture, mesh size effect etc. The objective here is to obtain optimum levels of effort, which gives the maximum yield that can be sustained over a long period