ACHIEVING SUSTAINABLE FISHERIES: GRADUALLY OR ABRUPTLY?

摘要

A key issue in fisheries restoration is the speed at which recovery can occur, while still meeting the economic and social constraints which managers must deal with. This paper uses the viable control approach to examine fisheries restoration and study the tradeoffs involved with the selection of recovery strategies. We define sustainability as a combination of biological, economic and social constraints which need to be met for a viable fishery to exist. The set of states for which constraints are met, or viable states, is considered as the target for recovery of the fishery. The analysis is based on a discrete time bioeconomic model of the Bay of Biscay nephrops fishery, with stock biomass and fleet size as the two state variables, and per vesselfishing effort and adjustment of fleet size as the two control variables. We address the particular optimal control problem of minimizing the time required for the fishery to recover from unsustainable states, under a minimum transition-profit constraintcorresponding to the need to maintain a minimum level of revenue for vessels during the transition phase. We apply this framework to a historical crisis situation in the case study, and analyze various recovery paths with different transition profit constraints, including the historical path followed by the fishery.