The East Atlantic and Mediterranean bluefin tuna stock management: uncertainties and alternatives

Jean-Marc Fromentin

doi:10.3989/scimar.2003.67s151

Abstract

Although the Atlantic bluefin tuna has been studied for more than a century, the assessment of the East stock is characterised by a large amount of uncertainty. In 2000, this situation became so critical that quantitative stock assessment has been postponed. The first part of the present study aims to list the main difficulties that have led to the current situation and tries to discern between subjective and objective uncertainty. The former, which is due to an incomplete knowledge of the system and which has increased in the past few years, is mainly due to a decreasing quality of the catch and effort data, that has followed the establishment of a TAC. The latter source of uncertainty, which results from the underlying variability in stochastic processes, mainly relates, for this species, to spatial and temporal changes in stock size, growth and migration. The second part of this study presents the results of simulation modelling, which could be, in the meantime, an useful tool for short-term management of the East Atlantic and Mediterranean BFT stock.

Highlights

In the last few years the Atlantic bluefin tuna (BFT) fisheries has become a highly profitable activity: one single fish can be sold for more than50,000 US$ on the Tokyo market and this situation has induced tensions between administrations, professionals and scientists
Discussion about the simulation modelling. All together these simulations gave three interesting indications: (i) stochastic variations in recruitment induce conspicuous long-term fluctuations in the stocks biomass (SSB) and yields; (ii) these pseudo-cycles and the age structure of this population make it more difficult to detect overfishing and depletion; and (iii) there is a clear interaction between age-at-maturity and fishing selectivity
We presented the main uncertainties related to the stock assessment and management of the Northeast Atlantic and Mediterranean bluefin tuna

Summary

Introduction

In the last few years the Atlantic bluefin tuna (BFT) fisheries has become a highly profitable activity: one single fish can be sold for more than50,000 US$ on the Tokyo market and this situation has induced tensions between administrations, professionals and scientists. In the last few years the Atlantic bluefin tuna (BFT) fisheries has become a highly profitable activity: one single fish can be sold for more than. The BFT fishery is, traditional in the Mediterranean Sea; the first evidences of tuna fishing are estimated at around. 7000 years BC (Desse and Desse-Berset, 1994; Doumenge, 1998) In relation to this long fishing history, bluefin tuna has been constantly studied. The ancient Greek and Latin philosophers Aristotle (fourth century BC) and Pliny (first century A.C.), already mentioned the BFT migration patterns in their natural history works and scientists have been studying the BFT biology and its fisheries since the late 19th century (e.g. Bragança, 1899; Sella, 1929; Rodriguez-Roda, 1964). A specific working group of scientists perform used to a complete stock assessment every 2 years since 1970. In 2000, the quantitative stock assessment procedure was, for the first time postponed, because of increasing uncertainties concern-

Results

Discussion

Conclusion