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Auteur Filmalter, J.D.; Cowley, P.D.; Potier, M.; Menard, F.; Smale, M.J.; Cherel, Y.; Dagorn, L.
Titre Feeding ecology of silky sharks Carcharhinus falciformis associated with floating objects in the western Indian Ocean Type Article scientifique
Année 2017 Publication Revue Abrégée J. Fish Biol.
Volume 90 Numéro 4 Pages 1321-1337
Mots-Clés atlantic; By-catch; diet; ecosystem; fad; fish aggregating devices; fish aggregation device; food-consumption; isurus-oxyrinchus; pacific-ocean; pelagic fishes; Pelagic shark; Purse-seine fishery; shortfin mako; Yellowfin tuna
Résumé The silky shark Carcharhinus falciformis is commonly associated with floating objects, including fish aggregating devices (FADs), in the Indian Ocean. While the motives for this associative behaviour are unclear, it does make them vulnerable to capture in the tuna purse seine fishery that makes extensive use of FADs. Here, the diet of 323 C. falciformis, caught at FADs in the Indian Ocean, was investigated to test the hypothesis that trophic benefits explain the associative behaviour. A high proportion of stomachs with fresh contents (57%) suggested that extensive feeding activity occurred while associated with FADs. Multiple dietary indices showed that typical non-associative prey types dominated, but were supplemented with fishes typically found at FADs. While the trophic benefits of FAD association may be substantial, our results suggest that associative behaviour is not driven solely by feeding. (C) 2016 The Fisheries Society of the British Isles
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ISSN 0022-1112 ISBN Médium
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Numéro d'Appel MARBEC @ alain.herve @ collection 2142
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Auteur Díez, G.; Moreno, G.; Galaz, T.; Dagorn, L.; Murua, J.
Titre Digestive activity and stomach temperature in farmed bluefin tuna Thunnus thynnus measured by acoustic tag Type Article scientifique
Année 2017 Publication Revue Abrégée J Fish Biol
Volume 90 Numéro 6 Pages 2504-2511
Mots-Clés acoustic; Bluefin tuna; digestion; farm; tag; Temperature
Résumé Eight farmed Atlantic bluefin tuna Thunnus thynnus were tagged with temperature and depth transmitters inserted in chub mackerels Scomber colias to characterize their digestive activity, feeding physiology and behaviour in captivity. Results obtained in the experiment can be used to optimize daily T. thynnus feeding strategy in farms, reducing the early regurgitation of food and thus the environmental effects of inappropriate feeding practices.
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ISSN 1095-8649 ISBN Médium
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 2145
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Auteur Rabearisoa, N.; Sabarros, P. S.; Romanov, E. V.; Lucas, V.; Bach, P.
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 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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ISSN 1932-6203 ISBN Médium
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 2401
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Auteur Robinson, J.; Guillotreau, P.; Jimenez-Toribio, R.; Lantz, F.; Nadzon, L.; Dorizo, J.; Gerry, C.; Marsac, F.
Titre Impacts of climate variability on the tuna economy of Seychelles Type Article scientifique
Année 2010 Publication Revue Abrégée Climate Research
Volume 43 Numéro Pages 149-162
Mots-Clés climate; economy; Enso; fisheries; Seychelles; tuna; variability
Résumé Many small island states have developed economies that are strongly dependent on tuna fisheries. Consequently, they are vulnerable to the socio-economic effects of climate change and variability, processes that are known to impact tuna fisheries distribution and productivity. The aim of this study was to assess the impacts of climate oscillations on the tuna-dependent economy of Seychelles. Using a multiplier approach, the direct, indirect and induced economic effects of the tuna industry expenditure benefiting the Seychelles' economy declined in 1998 by 58, 26 and 35%, respectively (mean decline: 42%), a year of strong climate oscillation in the western Indian Ocean. Multivariate patterns in tuna purse-seine vessel expenditures in port were substantially modified by strong climate oscillations, particularly in 1998. A cointegration time-series model predicted that a 40% decline in tuna landings and transhipment in Port Victoria, a value commensurate with that observed in 1998, would result in a 34% loss for the local economy solely through reductions in cargo handling expenditures. Of several indices tested, the Indian Oscillation Index was best at predicting the probability of switching between low and high regimes of landings and transhipment, which translate into impacts for the economy. It is hypothesised that a late 2006/early 2007 climate oscillation was compounded by prior overfishing to produce a stronger impact on the fishery and economy of Seychelles. The effects of fishing and climate variability on tuna fisheries are complex and pose significant challenges for fisheries management and the economic development of countries in the Indian Ocean.
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ISSN 0936-577x ISBN Médium
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Numéro d'Appel LL @ pixluser @ collection 101
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Auteur Lucena Frédou, F.; Frédou, T.; Gaertner, D.; Kell, L.; Potier, M.; Bach, P.; Travassos, P.; Hazin, F.; Ménard, F.
Titre Life history traits and fishery patterns of teleosts caught by the tuna longline fishery in the South Atlantic and Indian Oceans Type Article scientifique
Année 2016 Publication Revue Abrégée Fisheries Research
Volume 179 Numéro Pages 308-321
Mots-Clés Bycatch; Fishing impact; Tuna; Billfish; Ecosystem based fisheries management
Résumé The identification and mitigation of adverse effects of the bycatch of tuna longline fishery have been mainly developed and implemented for seabirds, sharks and turtles and, the knowledge on teleost bycatch for this fishery, remains very poor. This paper contributes to a comprehensive assessment of life history traits and fishery attributes of target and bycatch species caught by the tuna longline fishery in the South Atlantic and Indian Oceans. Data was compiled on seven life history traits and three fishery attributes for 33 and 27 teleost stocks caught by longliners in South Atlantic and Indian Oceans, respectively. In addition, each species was assigned into four categories describing the fate of the catch: target species for commercial use, bycatch species kept for consumption, bycatch species kept for commercial use and discarded bycatch. Life history traits and fishery attributes did not differ between oceans. However, non-target but commercialized species were smaller in the Atlantic Ocean. Teleosts caught by the tuna longline fishery was segregated into three main groups: (1) the fast growing species represented mainly by dolphinfishes (Coryphaena hippurus and C. equisellis), skipjack tuna (Katsuwonus pelamis), kawakawa (Euthynnus affinis), bullet tuna (Auxis rochei), snoek (Thyrsites atun) and blackfin tuna (Thunnus atlanticus); (2) target tunas and most other bycatch species which were part of an intermediate group and (3) billfishes including swordfish representing the large and slow growing species with moderate to high market values and unknown or highly uncertain stock status. Investment in some key life history traits (such as growth coefficient) and the development of quantitative or semi-quantitative approaches (stock assessment and Ecological Risk Assessment) should be priorized as precautionary management measures for these species.
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ISSN 0165-7836 ISBN Médium
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 2405
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