ABSTRACT

Vasconcellos, M.C. The complementary roles of single-species and ecosystem models in fisheries management. An example from a Southwest Atlantic fishery. FAO Fisheries Circular. No. 970. Rome, FAO. 2001. 38p. ABSTRACT Increasing concerns about the ecosystem impacts of fishing activities have motivated the development of ecosystem management principles which prompt a critical examination of concepts, methods and tools used in fisheries assessment and management. One of the central questions for fisheries assessment is how to evaluate and communicate the consequences of alternative fishing policies to marine resources and ecosystems, and therefore, what type of modeling approach to be used to this end. This work uses the fishery for the Brazilian sardine as a case study in the analysis of the roles of single-species and ecosystem models in the assessment and management of a capture fishery. The single-species approach combines functions representing growth, natural and fishing mortality, and three hypothesis proposed to explain sardine spawner-recruit population dynamics in a Monte Carlo simulation model. The ecosystem approach is based on the construction of an Ecopath mass-balance trophic model of the Southeastern Brazilian Bight, and the simulation in Ecosim of the changes in sardine biomass as affected directly by fishing and predation, and by changes in food availability, as well as indirectly by fishing and predation on other groups with which sardine interacts. Results of this analysis point at complementary roles of the two modeling approaches. Ecosystem models provide a more complete caricature of the system which is useful to evaluate the broad consequences of fishing policies, and to test and formulate hypotheses about the causes of observed changes in marine fish populations. The simpler structure and data requirements of single-species models make them useful for prediction of policy variables and monitoring purposes in the management of fisheries for a single stock. The combination of single-species and ecosystem models is a recommended strategy for improving estimates of policy parameters (e.g. Fmsy or F0.1) and for the evaluation of the importance of fisheries and environmental processes as causes of ecosystem changes in productivity.