Fisheries management based on ecosystem models

Abstract

The Ecopath model for the western North Pacific was constructed and some preliminary analyses were carried out in order to examine the usefulness of the model for multi-species management. Our Ecopath model consisted of 30 species groups based on the information that is mainly collected from published literature, Some Ecosim simulations showed non-trivial interaction between cetaceans and fishes and relative biomass of some cetaceans and fishes changed dramatically when their present harvest rates were changed in future. Fitting our model to the available abundance indices of some fishes indicated that the vulnerability parameter in the model was likely to be high. Further, additional simple simulation suggested that we could achieve targeted biomass of mackerel by adjusting the future harvest rate of cetaceans in place of that of mackerel. This indicates that multi-species management in the western North Pacific area might bring efficient fishing strategy. However, the results were very sensitive to setting of the vulnerability parameter. Therefore, Ecopath and Ecosim should not be considered as tools for multi-species management until uncertainty of important parameters is properly incorporated into Ecopath/Ecosim and the difference between them and a single-species model becomes clear. Nevertheless, those results from ecosystem models such as Ecopath and Ecosim are suggestive and valuable when they are brought up along with the result of single-species assessment.