Endogenous fishing mortalities: a state-space bioeconomic model

Abstract

A methodology that endogenously determines catchability functions that link fishing mortality with contemporaneous stock abundance is presented. We consider a stochastic age-structured model for a fishery composed by a number of fishing units (fleets, vessels or m ́etiers) that optimally select the level of fishing effort to be applied considering total mortalities as given. The introduction of a balance constrain which guarantees that total mortality is equal to the sum of individual fishing mortalities optimally selected, enables total fishing mortality to be determined as a combination of contemporaneous abundance and stochastic processes affecting the fishery. In this way, future abundance can be projected as a dynamic system that depends on contemporaneous abundance. The model is generic and can be applied to several issues of fisheries management. In particu- lar, we illustrate how to apply the methodology to assess the floating band target management regime inspired in the new multi-annual plans. Our results support this management regime for the Mediterranean demersal fishery in Northern Spain.