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Auteur |
Guillotreau, P.; Salladarre, F.; Dewals, P.; Dagorn, L. |
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Titre  |
Fishing tuna around Fish Aggregating Devices (FADs) vs free swimming schools : skipper decision and other determining factors |
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Article scientifique |
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Année |
2011 |
Publication |
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Revue Abrégée |
Fisheries Research |
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Volume |
109 |
Numéro |
2-3 |
Pages |
234-242 |
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Mots-Clés |
Fish Aggregating Devices; Purse-seine; Skipper effect; tuna |
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Résumé |
Fish Aggregating Devices (FADs) are increasingly used by tuna purse-seine fleets all around the world, modifying the species catch composition. We analyse the determinants of FAD vs free school (FS) fishing, including the skipper effect, and environmental and economic factors. A multivariate and econometric analysis of a panel dataset for the French purse-seine fleet in the Indian Ocean (1980-2007), complemented by a survey of fishers, demonstrates the influential role of climate and prey on FAD fishing and also emphasises individual skipper preference. However, we found that the major determinant of FAD fishing remains the growing fishing capacity (use of bigger vessels, satellite buoys, echo-sounders, supply vessels), thus modifying the species catch composition towards smaller tuna. Other things being equal, raising the proportion of FAD sets by 1% would increase the catches of skipjack by 1.3% and decrease those of large yellowfin tuna by 1.7%. This result shows that the control of effort and investment could be adapted through management measures to encourage one fishing method. |
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0165-7836 |
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LL @ pixluser @ |
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143 |
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Auteur |
Dueri, S.; Guillotreau, P.; Jiménez-Toribio, R.; Oliveros-Ramos, R.; Bopp, L.; Maury, O. |
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Titre |
Food security or economic profitability? Projecting the effects of climate and socioeconomic changes on global skipjack tuna fisheries under three management strategies |
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Article scientifique |
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Année |
2016 |
Publication |
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Revue Abrégée |
Global Environmental Change |
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Volume |
41 |
Numéro |
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Pages |
1-12 |
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Mots-Clés |
Bioeconomic model; climate change; fishery management; Mey; Msy; Skipjack tuna |
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Résumé |
We investigate the interactions between anthropogenic climate change, socioeconomic developments and tuna fishery management strategies. For this purpose, we use the APECOSM-E model to map the effects of climate change and commercial fishing on the distribution of skipjack tuna biomass in the three oceans, combined with a new bioeconomic module representing the rent or profit of skipjack fisheries. For forcing, we use Representative Concentration Pathway (RCP) 8.5, the highest emission scenario for greenhouse gas concentrations presented in the IPCC’s Fifth Assessment Report (AR5), and the IPCC Socioeconomic Shared Pathway (SSP) 3, which is characterized by low economic development and a strong increase in the world population. We first investigate the impact of climate change on regional skipjack abundance, catches and profits in three oceans (Atlantic, Indian and Pacific) in 2010, 2050 and 2095. We then study the effects of three management strategies (maximum sustainable yield or MSY, maximum economic yield or MEY, and zero rent or ZR) on the future distribution of fishing fleets between oceans and on global economic rent. Our model projections for 2050 and 2095 show an increase in global skipjack biomass compared to 2010 and major changes in its distribution, impacting local and regional fishing efforts. The Pacific Ocean will continue to dominate the skipjack market. In our modeling of management strategies, the currently predominant MSY strategy would have been unprofitable in 2010, due to a decreased catch per unit effort (CPUE). In the future, however, technological developments should increase fishing efficiency and make MSY profitable. In all the scenarios, a MEY strategy is more profitable than MSY but leads to the lowest catches and the highest prices. This raises ethical questions in a world where food security may become a top priority. In the scenarios where MSY generates an economic loss (e.g. 2010), a ZR strategy allows global stocks to be exploited at high but still profitable levels. Conversely, in the scenarios where MSY is profitable, (e.g. 2095) ZR leads to overfishing and smaller global catches. We conclude that the most appropriate management strategy at any time is likely to change as environmental and socioeconomic conditions evolve. The decision to follow one or other strategy is a complex one that must be regularly reviewed and updated. |
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0959-3780 |
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Numéro d'Appel |
MARBEC @ isabelle.vidal-ayouba @ |
collection |
1601 |
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Auteur |
Escalle, L.; Gaertner, D.; Chavance, P.; Delgado de Molina, A.; Ariz, J.; Mérigot, B. |
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Titre |
Forecasted consequences of simulated FAD moratoria in the Atlantic and Indian Oceans on catches and bycatches |
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Article scientifique |
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Année |
2017 |
Publication |
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Revue Abrégée |
ICES J. Mar. Sci. |
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Volume |
74 |
Numéro |
3 |
Pages |
780-792 |
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Mots-Clés |
area; Bycatch; ecosystem approach to fisheries; fish aggregation device; management; Megafauna; Monte Carlo simulations; Purse-seine fishery; time; time-area restriction; tropical tuna purse-seine fishery; Tuna |
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Résumé |
Given the increasingly extensive use of drifting fish aggregation devices (FADs) by the purse-seine fisheries targeting tropical tunas, fishing effort restrictions have been introduced to manage tropical tuna stocks. However, these measures are focused on the protection of juvenile tunas and do not take account of the potential impact on bycatch or associated megafauna (whales and whale sharks). An iterative “fishing-day” Monte Carlo simulation model was developed to investigate the consequences on tropical tunas and bycatch of introducing extensive area 6-month moratoria on FAD activities. The model allowed for variability in a range of plausible values of the parameters characterizing the fishing operations conducted by European purse-seiners in the eastern tropical Atlantic and western Indian Oceans for the period 2005-2014. Monte Carlo simulations, using probabilities based on these fishery data, were carried out for the French and Spanish fishing fleets separately to account for differences in fishing strategies. The models predicted a decrease in FAD sets and an increase in free school sets. As a consequence, the catch of small tuna (<10 kg) decreased while the catch of large tuna (>= 10 kg) increased, leading to an overall increase in tuna catch of 100-200 tons/year/vessel in the Atlantic Ocean, and a decrease of 400-1500 tons/year/vessel in the Indian Ocean. The bycatch decreased in the Indian Ocean, while in the Atlantic Ocean billfishes, turtles and chondrichthyans bycatch increased slightly and other bony fishes decreased. Because fishing practices were modified, whale and whale shark associated sets increased slightly in the Indian Ocean. |
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English |
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ISSN |
1054-3139 |
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Numéro d'Appel |
MARBEC @ alain.herve @ |
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2105 |
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Auteur |
Walker, E.; Rivoirard, J.; Gaspar, P.; Bez, N. |
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Titre |
From forager tracks to prey distributions: an application to tuna vessel monitoring systems (VMS) |
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Article scientifique |
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Année |
2015 |
Publication |
Ecological Applications |
Revue Abrégée |
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Volume |
25 |
Numéro |
3 |
Pages |
826-833 |
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Mots-Clés |
Gps; multivariate geostatistics; presence index; spatiotemporal distribution; trajectometry; Tropical tuna; vessel monitoring system (VMS) |
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In the open ocean, movements of migratory fish populations are typically surveyed using tagging methods that are subject to low sample sizes for archive tags, except for a few notable examples, and poor temporal resolution for conventional tags. Alternatively, one can infer patterns of movement of migratory fish by tracking movements of their predators, i.e., fishing vessels, whose navigational systems (e.g., GPS) provide accurate and frequent VMS (vessel monitoring system) records of movement in pursuit of prey. In this paper, we develop a state-space model that infers the foraging activities of fishing vessels from their tracks. Second, we link foraging activities to probabilities of tuna presence. Finally, using multivariate geostatistical interpolation (cokriging) we map the probability of tuna presence together with their estimation variances and produce a time series of indices of abundance. While the segmentation of the trajectories is validated by observers' data, the present VMS-index is compared to catch rate and proved to be useful for management perspectives. The approach reported in this manuscript extends beyond the case study considered. It can be applied to any foragers that engage in an attempt of capture when they see prey and for whom this attempt is linked to a tractable change in behavior. |
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1051-0761 |
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MARBEC @ isabelle.vidal-ayouba @ |
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1116 |
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Auteur |
NIEBLAS, A.-E.; DEMARCQ, H.; DRUSHKA, K.; SLOYAN, B.; BONHOMMEAU, S. |
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Titre |
Front variability and surface ocean features of the presumed southern bluefin tuna spawning grounds in the tropical southeast Indian Ocean |
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Article scientifique |
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Année |
2014 |
Publication |
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Revue Abrégée |
Deep-sea Research Part II-topical Studies In Oceanography |
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Volume |
107 |
Numéro |
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64-76 |
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Mots-Clés |
Front detection index; Indo-Australian region; Oceanic fronts; Southern bluefin tuna Thunnus maccoyii; Spawning grounds (10 degrees S-20 degrees S 105 degrees E-125 degrees E); Tropical southeast Indian Ocean |
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Résumé |
The southern bluefin tuna (SBT, Thunnus maccoyii) is an ecologically and economically valuable fish. However, surprisingly little is known about its critical early life history, a period when mortality is several orders of magnitude higher than at any other life stage, and when larvae are highly sensitive to environmental conditions. Ocean fronts can be important in creating favourable spawning conditions, as they are a convergence of water masses with different properties that can concentrate planktonic particles and lead to enhanced productivity. In this study, we examine the front activity within the only region where SBT have been observed to spawn: the tropical southeast Indian Ocean between Indonesia and Australia (10 degrees S-20 degrees S, 105 degrees E-125 degrees E). We investigate front activity and its relationship to ocean dynamics and surface features of the region. Results are also presented for the entire Indian Ocean (30 degrees N-45 degrees S, 20 degrees E-140 degrees E) to provide a background context. We use an extension of the Cayula and Cornillon algorithm to detect ocean fronts from satellite images of sea surface temperature (SST) and chlorophyll-a concentration (chl-a). Front occurrence represents the probability of occurrence of a front at each pixel of an image. Front intensity represents the magnitude of the difference between the two water masses that make up a front. Relative to the rest of the Indian Ocean, both SST and chl-a fronts in the offshore spawning region are persistent in occurrence and weak in intensity. Front occurrence and intensity along the Australian coast are high, with persistent and intense fronts found along the northwest and west coasts. Fronts in the tropical southeast Indian Ocean are shown to have strong annual variability and some moderate interannual variability. SST front occurrence is found to lead the Southern Oscillation Index by one year, potentially linked to warming and wind anomalies in the Indian Ocean. The surface ocean characteristics of the offshore SBT spawning region are found to be particularly stable compared to the rest of the Indian Ocean in terms of stable SST, low eddy kinetic energy, i.e., low mesoscale eddy activity, and low chl-a. However, this region has high front occurrence, but low front intensity of both SST and chl-a fronts. The potential impact of these oceanic features for SBT spawning is discussed. |
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0967-0645 |
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MARBEC @ isabelle.vidal-ayouba @ |
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1131 |
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