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Auteur Amandé, M.; Ariz, J.; Chassot, E.; Molina, A.D. de; Gaertner, D.; Murua, H.; Pianet, R.; Ruiz, J.; Chavance, P. url  doi
openurl 
  Titre Bycatch of the European purse seine tuna fishery in the Atlantic Ocean for the 2003-2007 period Type Article scientifique
  Année 2010 Publication Revue Abrégée Aquatic Living Resources  
  Volume 23 Numéro 4 Pages 353-362  
  Mots-Clés atlantic Ocean; Bycatch; discards; Purse seining; Tuna fisheries  
  Résumé (up) Bycatch of several groups of species and their characteristics are presented for the period 2003 to 2007 for the European purse seine tuna fishery operating in the Atlantic Ocean. Data were collected through French and Spanish observer programmes and represented a total of 27 trips corresponding to 2.9% coverage. Bycatch is defined as non-targeted species and small or damaged target species. Bycatch species composition, main species length, sex ratio and the fate of the most common species are presented first. Stratified ratios relative to landings of major commercial tunas were then used to estimate the total bycatch; these ratios were considered the most appropriate variable for extrapolation. Stratification was based on the fishing mode (free school vs. floating object), season (quarters) and spatial areas. The annual average bycatch was estimated at about 6400 t, corresponding to a mean annual value of 80.8 t per 1000 t of tuna landed or 7.5% of the total catch. Tunas represent 83% (67.2 t/1000 t) of the total bycatch, followed by other bony fishes (10%, 7.8 t/1000 t), billfishes (5%, 4.0 t/1000 t), sharks (1%, 0.9 t/1000 t) and rays (1%, 0.9 t/1000 t). Based on estimates of the annual bycatch, 16% was kept on board and sold in local markets.  
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  Langue Langue du Résumé Titre Original  
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  Volume de collection Numéro de collection Edition  
  ISSN 0990-7440 ISBN Médium  
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  Numéro d'Appel LL @ pixluser @ collection 56  
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Auteur Gaertner, D. url  doi
openurl 
  Titre Estimates of historic changes in total mortality and selectivity for Eastern Atlantic skipjack (Katsuwonus pelamis) from length composition data Type Article scientifique
  Année 2010 Publication Revue Abrégée Aquatic Living Resources  
  Volume 23 Numéro Pages 3-11  
  Mots-Clés analysis; Bayesian; change-point; Fad; Fishing; Mortality; rate; Skipjack; strategies; tuna  
  Résumé (up) Catch-at-size data of the eastern Atlantic skipjack were used to estimate changes in total mortality from 1969 to 2007. We used a transitional model of mean length that generalized the Beverton-Holt mortality estimator to allow change in mortality rate under nonequilibrium conditions. Then, from homogeneous periods of time, length-converted catch curves were used to access qualitative changes in selectivity patterns for two surface fisheries (the baitboat fishery operating from Dakar, Senegal, and the European and associated purse seine fisheries). To explore the impact of catch on the mortality rate, a Bayesian change-point analysis was conducted on the catch time series to detect concomitant variation between mortality rates and catch. Finally, potential causes of these changes are discussed in relation to the implementation of new fishing technology, such fish aggregating devices (FAD). The general pattern depicted by total mortality is in agreement with previous knowledge on this fishery: a state of complete or practically complete exploitation during the nineties followed by the decrease in nominal purse seine fishing effort in the last decade, combined with the effect of a seasonal moratorium on FAD fishing operations. There was no evidence of a change in selectivity between the two contrasted periods of time considered: 1969-1979 and 1986-1999; the second period being characterized by the introduction of new technology onboard vessels. In contrast, the covariation over time between total catch and mortality rate three years later highlights the effect of the fishing pressure on the stock of eastern Atlantic skipjack.  
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  Volume de collection Numéro de collection Edition  
  ISSN 0990-7440 ISBN Médium  
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  Numéro d'Appel LL @ pixluser @ collection 74  
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Auteur Dueri, S.; Bopp, L.; Maury, O. url  doi
openurl 
  Titre Projecting the impacts of climate change on skipjack tuna abundance and spatial distribution Type Article scientifique
  Année 2014 Publication Revue Abrégée Global Change Biology  
  Volume 20 Numéro 3 Pages 742-753  
  Mots-Clés Apecosm-E; Atlantic Ocean; global warming; Indian Ocean; Katsuwonus pelamis; Pacific Ocean; scenario; Tropical tuna  
  Résumé (up) Climate-induced changes in the physical, chemical, and biological environment are expected to increasingly stress marine ecosystems, with important consequences for fisheries exploitation. Here, we use the APECOSM-E numerical model (Apex Predator ECOSystem Model – Estimation) to evaluate the future impacts of climate change on the physiology, spatial distribution, and abundance of skipjack tuna, the worldwide most fished species of tropical tuna. The main novelties of our approach lie in the mechanistic link between environmental factors, metabolic rates, and behavioral responses and in the fully three dimensional representation of habitat and population abundance. Physical and biogeochemical fields used to force the model are provided by the last generation of the IPSL-CM5 Earth System Model run from 1990 to 2100 under a &8216;business-as-usual&8217; scenario (RCP8.5). Our simulations show significant changes in the spatial distribution of skipjack tuna suitable habitat, as well as in their population abundance. The model projects deterioration of skipjack habitat in most tropical waters and an improvement of habitat at higher latitudes. The primary driver of habitat changes is ocean warming, followed by food density changes. Our projections show an increase of global skipjack biomass between 2010 and 2050 followed by a marked decrease between 2050 and 2095. Spawning rates are consistent with population trends, showing that spawning depends primarily on the adult biomass. On the other hand, growth rates display very smooth temporal changes, suggesting that the ability of skipjack to keep high metabolic rates in the changing environment is generally effective. Uncertainties related to our model spatial resolution, to the lack or simplification of key processes and to the climate forcings are discussed.  
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  Volume de collection Numéro de collection Edition  
  ISSN 1354-1013 ISBN Médium  
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  Numéro d'Appel LL @ pixluser @ collection 327  
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Auteur Pons, M.; Branch, T.A.; Melnychuk, M.C.; Jensen, O.P.; Brodziak, J.; Fromentin, J.M.; Harley, S.J.; Haynie, A.C.; Kell, L.T.; Maunder, M.N.; Parma, A.M.; Restrepo, V.R.; Sharma, R.; Ahrens, R.; Hilborn, R. url  doi
openurl 
  Titre Effects of biological, economic and management factors on tuna and billfish stock status Type Article scientifique
  Année 2017 Publication Revue Abrégée Fish Fish  
  Volume 18 Numéro 1 Pages 1-21  
  Mots-Clés Fisheries management; marine conservation; stock assessment; stock status; Tuna fisheries  
  Résumé (up) Commercial tunas and billfishes (swordfish, marlins and sailfish) provide considerable catches and income in both developed and developing countries. These stocks vary in status from lightly exploited to rebuilding to severely depleted. Previous studies suggested that this variability could result from differences in life-history characteristics and economic incentives, but differences in exploitation histories and management measures also have a strong effect on current stock status. Although the status (biomass and fishing mortality rate) of major tuna and billfish stocks is well documented, the effect of these diverse factors on current stock status and the effect of management measures in rebuilding stocks have not been analysed at the global level. Here, we show that, particularly for tunas, stocks were more depleted if they had high commercial value, were long-lived species, had small pre-fishing biomass and were subject to intense fishing pressure for a long time. In addition, implementing and enforcing total allowable catches (TACs) had the strongest positive influence on rebuilding overfished tuna and billfish stocks. Other control rules such as minimum size regulations or seasonal closures were also important in reducing fishing pressure, but stocks under TAC implementations showed the fastest increase of biomass. Lessons learned from this study can be applied in managing large industrial fisheries around the world. In particular, tuna regional fisheries management organizations should consider the relative effectiveness of management measures observed in this study for rebuilding depleted large pelagic stocks.  
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  ISSN 1467-2979 ISBN Médium  
  Région Expédition Conférence  
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  Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 2079  
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Auteur Rabearisoa, N.; Sabarros, P. S.; Romanov, E. V.; Lucas, V.; Bach, P. url  doi
openurl 
  Titre Toothed whale and shark depredation indicators: A case study from the Reunion Island and Seychelles pelagic longline fisheries Type Article scientifique
  Année 2018 Publication Revue Abrégée PLOS ONE  
  Volume 13 Numéro 8 Pages e0202037  
  Mots-Clés Indian Ocean; Seychelles; Sharks; Tuna; Fisheries; Economics; Killer whales; Whales  
  Résumé (up) Depredation in marine ecosystems is defined as the damage or removal of fish or bait from fishing gear by predators. Depredation raises concerns about the conservation of species involved, fisheries yield and profitability, and reference points based on stock assessment of depredated species. Therefore, the development of accurate indicators to assess the impact of depredation is needed. Both the Reunion Island and the Seychelles archipelago pelagic longline fisheries targeting swordfish (Xiphias gladius) and tuna (Thunnus spp.) are affected by depredation from toothed whales and pelagic sharks. In this study, we used fishery data collected between 2004 and 2015 to propose depredation indicators and to assess depredation levels in both fisheries. For both fisheries, the interaction rate (depredation occurrence) was significantly higher for shark compared to toothed whale depredation. However, when depredation occurred, toothed whale depredation impact was significantly higher than shark depredation impact, with higher depredation per unit effort (number of fish depredated per 1000 hooks) and damage rate (proportion of fish depredated per depredated set). The gross depredation rate in the Seychelles was 18.3%. A slight increase of the gross depredation rate was observed for the Reunion Island longline fleet from 2011 (4.1% in 2007–2010 and 4.4% in 2011–2015). Economic losses due to depredation were estimated by using these indicators and published official statistics. A loss of 0.09 EUR/hook due to depredation was estimated for the Reunion Island longline fleet, and 0.86 EUR/hook for the Seychelles. These results suggest a southward decreasing toothed whale and shark depredation gradient in the southwest Indian Ocean. Seychelles depredation levels are among the highest observed in the world revealing this area as a “hotspot” of interaction between pelagic longline fisheries and toothed whales. This study also highlights the need for a set of depredation indicators to allow for a global comparison of depredation rates among various fishing grounds worldwide.  
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  Langue en Langue du Résumé Titre Original  
  Éditeur de collection Titre de collection Titre de collection Abrégé  
  Volume de collection Numéro de collection Edition  
  ISSN 1932-6203 ISBN Médium  
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  Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 2401  
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