Stochastic Bio-Economic Model of Northern Atlantic and Mediterranean Bluefin Tuna

Abstract

The purpose of this paper is to study the implications of introducing a stochastic stock in a multi-gear and age structured bio-economic model for the Northern Atlantic Bluefin tuna. In order to account for variations on the recruitment, uncertainty is introduced on a bilinear recruitment function, and it is represented by an exponential random error term leading the stock to be, on average, higher than in the deterministic case. Both the bionomic equilibrium and the optimal management of this species are examined. In the latter, two alternative instruments are studied: the constant total allowable catch and the constant effort and the purpose is to maximize the expected total net present value. The conclusions enhance that the results do not differ significantly from those in the deterministic model, that is, the fishing effort should be the policy instrument to adopt, both in the East and the West Atlantic. Despite the previous reasoning, the shock on recruitment should be taken into account, as certain realizations of the random variable may lead to different results. In particular, for low Bluefin tuna stock levels, it is optimal to regulate the caches instead of the fishing effort, to ensure the stock recovery.