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

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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.