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| Bonhommeau, Sylvain; Fromentin, Jean-marc. |
| This study aims at examining the potential bias in the VPA estimates by simulating a population, catch and CPUEs over 39 years from 1970 to 2008. In the operational model, two levels of noise were added to catch and CPUEs (50 and 100%), three fishing patterns were explored (F=FMSY, F increases linearly from 0.5 FMSY to 2.5 FMSY, F increases linearly from 0.5 FMSY to 2.5 FMSY over the first 34 years and decreases down to FMSY over the last 5 years). We also tested different hypothesis about the impact of the terminal F-ratios, and the natural mortality used in the current VPA as well as the impact of randomly generated CPUE for long-line and trap CPUE. Results show that the VPA is robust to estimate the SSB whatever the noise level in the catch and the... |
| Tipo: Text |
Palavras-chave: Bluefin tuna; Stock assessment; VPA; Management regulations; TAC. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00192/30280/28755.pdf |
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| Fromentin, Jean-marc. |
| The aim of this study is to investigate the implications of different stock-recruitment assumptions when examining the potential of Dubrovnik’s bluefin tuna recovery plan. To do so, some Beverton and Holt relationships displaying contrasting steepness of 0.99, 0.90, 0.75 and 0.50 were applied within a simulation model. In addition to these four stock-recruitment scenarios, parental effects and stochastic variations were also considered. The main conclusion is that our ability to evaluate the consequences of the Dubrovnik agreement (as any set of management measures) relies on our capacity to predict future recruitment levels in an accurate way. Assuming a Beverton and Holt relationship with different steepness, with or without parental effects and with or... |
| Tipo: Text |
Palavras-chave: Thunnus thynnus; Management regulations; Stock-recruitment; Parental effects; Stock rebuilding; Simulation model. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/00192/30296/28784.pdf |
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| Fromentin, Jean-marc. |
| This manuscript proposes a simple simulation model to investigate the implications to the resources of the recent management regulations adopted for the East Atlantic and Mediterranean bluefin tuna stock. If perfectly implemented, the new regulations on minimum size and closed fishing areas mostly lead to a change in the selectivity pattern which moves towards older fish, so decreasing growth-overfishing. The potential sustainable yields therefore considerably increase (almost double in comparison to those that would be obtained without the new regulations) while the SSB can rapidly reach 20% of the virgin SSB. An error of 20% in the implementation of these new regulations affects their efficiencies and does not seem to allow the rebuilding of the SSB at a... |
| Tipo: Text |
Palavras-chave: Bluefin tuna; Management regulations; Stock rebuilding; Simulation model. |
| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/00192/30297/28787.pdf |
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