Community Research and Development Information Service - CORDIS

Research publication: Consequences of variations in carry capacity or migration on population of Atlantic Bluefin tuna

Spectacular long-term fluctuations (of the order of 110 years) have been seen in catches of Atlantic bluefin tuna (Thunnus thynnus) independent of human exploitation. The actual causes of such changes could have been generated by contrasting but equally plausible dynamic processes, such as changes in carrying capacity or migration. A simulation framework was therefore used to evaluate the consequences for the perception of the stock obtained via virtual population analysis (VPA) as used by ICCAT.

It was shown that the performances of VPA depend on the underlying processes that generated the long-term fluctuations in catch and on the current phase of the dynamics, both of which will be extremely difficult if not impossible to determine from current stock assessment methods. Further, while interpretation of variation in catch resulting from changes in the carrying capacity can be estimated correctly by VPA, it is more difficult to estimate trends and absolute values of fishing mortality and spawning stock biomass when variations in catch result from changes in migration.

There was also considerable confounding between the dynamics and increasing effort, as currently seen, that makes it difficult to infer the actual dynamics on the basis of commercial catch data. The main outcome of the study is that knowledge of the underlying process that generates long-term variations in catch is of key importance, because distinct processes lead to contrasting population dynamics and to different perceptions of stock status.

Reported by

IFREMER - Centre de Recherche Halieutique Méditerranéen et Tropical
Avenue Jean Monnet
34203 Sète cedex
France
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