Recovering Sustainable Fisheries

Abstract

In this paper, we study recovering processes for fisheries facing crisis or over-exploitation of a marine renewable resource. We examine how to restore resource stocks and modify the economic characteristics of the fleet in order to put on a sustainable exploitation system, near of some maximal standard as the Maximum Sustainable Yield. We define the sustainability of the exploitation with respect to both economic and biological constraints. Biological constraints are bases on the definition of a minimal resource stock to be preserved in order to insure the resource regeneration. Economic constraints include a minimal size for the fleet (number of vessels, which induces a social constraint on the employment) and a minimal profit per boat. We use the viability framework to consider the favorable situations of the bio-economic system in which a sustainable exploitation is possible, i.e. viable states that make it possible to satisfy the co-viability conditions in the long run, taking into account dynamical properties of the system. Along with the definition of such favorable states, we examine transition phases to reach sustainable configurations from a crisis situation. We characterize the recovering paths studying the economic cost of limiting catches during recovery period, and the length of this transition period. The developed framework makes it possible to study the sensitivity of the various constraints on that cost and time, and to minimize either one or the other. To avoid recurrence of the over-exploitation problems, we characterize sustainable decisions associated with viable states, for the dynamical evolution of the system. It includes decisions on the effort allocated to each vessel, and decisions on the modification of the size of the fleet. We develop a global model for a single resource stock. As an illustration, we study the recovering of the Nephrops stocks in the Bay of Biscay, taking into account both conceptual and applied issues