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| Registros recuperados: 129 | |
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| Fromentin, Jean-marc; Kell, L. |
| Spectacular long-term cycles (around 110 years), independent of human exploitation, have been seen in historical catches of Atlantic bluefin tuna (Thunnus thynnus). Previous studies indicated that such variations could have been generated by contrasting but equally plausible dynamic processes, i.e., changes in carrying capacity or migration. A simulation framework was therefore used to test whether the International Commission for the Conservation of Atlantic Tuna stock assessment model, i.e., a virtual population analysis (VPA), can capture such dynamics. The main outcome is that knowledge of the underlying process is crucial, because distinct hypotheses lead to different population dynamics and contrasting performances of the stock assessment model. The... |
| Tipo: Text |
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| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-3533.pdf |
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| Fromentin, Jean-marc; Fonteneau, Alain. |
| This study aims to test whether exploitation affects tunas and tuna-like species displaying contrasting life history traits similarly. We first collected information on life history of 10 commercial Atlantic species and then compared this information using multivariate analysis. On one hand, tropical tunas are characterised by small to medium size, rapid growth, early age-at-maturity, long spawning duration and short life span. These species, therefore, display a rapid turnover, characteristic of r-selected species. On the other hand, temperate tunas display differing life history traits, i.e., large size, slow growth, late age-at-maturity, short spawning duration and long life span. The turnover of these species is slow and present characteristics similar... |
| Tipo: Text |
Palavras-chave: Management measures; Sustainability; Fishing; Long term fluctuations; Simulation modelling; Skipjack; Bluefin tuna. |
| Ano: 2001 |
URL: http://archimer.ifremer.fr/doc/2001/publication-434.pdf |
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| Simon, Maximilien; Fromentin, Jean-marc; Bonhommeau, Sylvain; Gaertner, Daniel; Brodziak, Jon; Etienne, Marie-pierre. |
| The intrinsic population growth rate (r) of the surplus production function used in the biomass dynamic model and the steepness (h) of the stock-recruitment relationship used in age-structured population dynamics models are two key parameters in fish stock assessment. There is generally insufficient information in the data to estimate these parameters that thus have to be constrained. We developed methods to directly estimate the probability distributions of r and h for the Atlantic bluefin tuna (Thunnus thynnus, Scombridae), using all available biological and ecological information. We examined the existing literature to define appropriate probability distributions of key life history parameters associated with intrinsic growth rate and steepness, paying... |
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| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00115/22640/20362.pdf |
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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; Bonhommeau, Sylvain. |
| This study aims at examining the selectivity patterns among gears and years of the fleets targeting bluefin tuna in the Northeast Atlantic and Mediterranean Sea between 1970 and 2009, using catch curve analyses. The main outputs may be summarized as follow: (i) the general pattern of selectivity has highly varied through time, moving from ages 1-3 to ages 10+ from the 1970s to the 2000s; (ii) this important temporal drift primarily resulted from changes in PS selectivity patterns; (iii) these drastic variations in selectivity among gears and years can affect simple indicators which do not incorporate such information; (iv) the catch-at-age (CAA) matrix seems to be impaired by several inconsistencies that affect primarily the partial CAA of the purse... |
| Tipo: Text |
Palavras-chave: Gear selectivity; Stock assessment; Bluefin tuna. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00192/30279/28747.pdf |
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| Rouyer, Tristan; Fromentin, Jean-marc; Stenseth, Nils Chr.. |
| Environmental variables affect many processes of fish biology and their fluctuations are thought to be one of the main factors in variability of fish stocks. Recent work has shown that the variability of the environment in the frequency domain (i.e., the environmental noise) can interact with endogenous processes (e.g., density dependence) and affect fluctuations of animal populations. In this study, we investigate whether fluctuations of large pelagics' time series are affected by environmental noise and whether life-history traits of species modulate this response. By analysing several environmental variables and a large dataset of tuna and billfish catch per unit effort (CPUE) time series from the Atlantic, we show that in environments dominated by... |
| Tipo: Text |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00011/12230/9083.pdf |
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| Fromentin, Jean-marc. |
| The 2001 size composition of Atlantic bluefin tuna catches of the French purse seiners has been estimated from the EU log-books and appears roughly in agreement with those estimated from the local seafood traders between 1982 and 1998. However, the accuracy of the 2001 size composition remains uncertain because of a lack of a standard protocol and of sampling on catch coming from heterogeneous and/or multiple shoals. Regarding the spatial and temporal dynamic of the French fishery, an observer program should be implemented to correct and validate the size frequencies of these catches. |
| Tipo: Text |
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| Ano: 2002 |
URL: http://archimer.ifremer.fr/doc/00194/30526/28938.pdf |
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| Registros recuperados: 129 | |
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