| Enregistrements |
| 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 |
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Revue Abrégée |
Climate Research |
| Volume |
43 |
Numéro |
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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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0936-577x |
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LL @ pixluser @ |
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101 |
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Salvetat, J.; Lebourges-Dhaussy, A.; Travassos, P.; Gastauer, S.; Roudaut, G.; Vargas, G.; Bertrand, A. |
| Titre |
In situ target strength measurement of the black triggerfish Melichthys niger and the ocean triggerfish Canthidermis sufflamen |
Type |
Article scientifique |
| Année |
2020 |
Publication |
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Revue Abrégée |
Mar. Freshw. Res. |
| Volume |
71 |
Numéro |
9 |
Pages |
1118-1127 |
| Mots-Clés |
acoustics; aggregating devices fads; archipelago; atlantic; behavior; biomass estimation; frequency; north-east Brazil; shore fishes; small tuna; spinner dolphins; swimbladder; target strength-length relationships; tropical ecosystem; tropical tuna; underwater acoustics; underwater video |
| Résumé |
Triggerfish are widely distributed in tropical waters where they play an important ecological role. The black triggerfish Melichthys niger may be the dominant species around oceanic tropical islands, whereas pelagic triggerfish, such as the ocean triggerfish Canthidermis sufflamen, can assemble around fish aggregating devices (FADs) where they are a common bycatch of tuna fisheries. In this study we combined acoustic and optical recordings to provide the first in situ target strength (TS) measurement of black and ocean triggerfish. Data were collected in the Archipelago of Fernando de Noronha off north-east Brazil. The mean TS of a 27.8-cm-long black triggerfish at 70 and 200 kHz was -39.3 dB re 1 m(2) (CV = 14.0%) and -38.9 dB re 1 m(2) (CV = 14.4%) respectively. The mean TS values of ocean triggerfish (with a size range of 39-44 cm) at 70 and 200 kHz were -36.0 dB re 1 m(2) (CV = 15.7%) and -33.3 dB re 1 m(2) (CV = 14.0%) respectively. This work opens up the field for acoustic biomass estimates. In addition, we have shown that TS values for ocean triggerfish are within the same range as those of small tunas. Therefore, acoustic data transmitted from FADs equipped with echosounders can introduce a bias in tuna acoustic biomass estimation and lead to increased rates of bycatch. |
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English |
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1323-1650 |
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WOS:000562536400007 |
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pas de |
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MARBEC @ isabelle.vidal-ayouba @ |
collection |
2872 |
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| Auteur |
Dagorn, L.; Holland, K.N.; Restrepo, V.; Moreno, G. |
| Titre |
Is it good or bad to fish with FADs? What are the real impacts of the use of drifting FADs on pelagic marine ecosystems? |
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Article scientifique |
| Année |
2013 |
Publication |
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Revue Abrégée |
Fish And Fisheries |
| Volume |
14 |
Numéro |
3 |
Pages |
391-415 |
| Mots-Clés |
by-catch; ecological trap; Fad; purse seine; tuna |
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The use of fish aggregating devices (FADs) by purse seine fisheries has come under increasing criticism for its potential deleterious impacts on tuna stocks, for high levels of by-catch and threats to the biodiversity of tropical pelagic ecosystems. Here, we review the current state of scientific knowledge of this fishing technique and current management strategies. Our intent is to encourage objective discussion of the topic and highlight areas worthy of future research. We show that catching juvenile tuna around FADs does not necessarily result in overfishing of stocks, although more selective fishing techniques would likely help obtain higher yield. Levels of non-tuna by-catch are comparable to or less than in other commercial tuna fisheries and are primarily comprised of species that are not considered threatened. Accordingly, to minimize impacts on ecosystem balance, there is merit in considering that all species captured in purse seine fisheries (excluding vulnerable species such as turtles and sharks) should be retained, but the consequences of such a measure should be carefully examined before implementation. The take of vulnerable species could be further reduced by introduction of additional mitigation measures, but their potential benefits would be limited without parallel efforts with other gears. Finally, there is no unequivocal empirical evidence that FADs represent an ‘ecological trap’ that inherently disrupts tuna biology although further research should focus on this issue. We encourage RFMOs to expand and improve their FAD management plans. Under appropriate management regimes, FAD fishing could be an ecologically and economically sensible fishing method. |
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en |
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1467-2979 |
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pas de |
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LL @ pixluser @ |
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256 |
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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 |
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Revue Abrégée |
Fisheries Research |
| Volume |
179 |
Numéro |
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Pages |
308-321 |
| Mots-Clés |
Bycatch; Fishing impact; Tuna; Billfish; Ecosystem based fisheries management |
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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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0165-7836 |
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MARBEC @ isabelle.vidal-ayouba @ |
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2405 |
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| Auteur |
Baidai, Y.; Dagorn, L.; Amande, M.J.; Gaertner, D.; Capello, M. |
| Titre |
Machine learning for characterizing tropical tuna aggregations under Drifting Fish Aggregating Devices (DFADs) from commercial echosounder buoys data |
Type |
Article scientifique |
| Année |
2020 |
Publication |
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Revue Abrégée |
Fish Res. |
| Volume |
229 |
Numéro |
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Pages |
105613 |
| Mots-Clés |
behavior; classification; communities; Direct abundance indicator; echo-sounder buoys; Echosounder buoys; estimate biomass; fads; Fish aggregating devices; Purse seiner; purse seiners; target strength; temperature; Tropical tunas; yellowfin thunnus-albacares |
| Résumé |
The use of echosounder buoys deployed in conjunction with Drifting Fish Aggregating Devices (DFADs) has progressively increased in the tropical tuna purse seine fishery since 2010 as a means of improving fishing efficiency. Given the broad distribution of DFADs, the acoustic data provided by echosounder buoys can provide an alternative to the conventional CPUE index for deriving trends on tropical tuna stocks. This study aims to derive reliable indices of presence of tunas (and abundance) using echosounder buoy data. A novel methodology is presented which utilizes random forest classification to translate the acoustic backscatter from the buoys into metrics of tuna presence and abundance. Training datasets were constructed by cross-referencing acoustic data with logbook and observer data which reported activities on DFADs (tuna catches, new deployments and visits of DFADs) in the Atlantic and Indian Oceans from 2013 to 2018. The analysis showed accuracies of 75 and 85 % for the recognition of the presence/absence of tuna aggregations under DFADs in the Atlantic and Indian Oceans, respectively. The acoustic data recorded at ocean-specific depths (6-45m in the Atlantic and 30-150m in the Indian Ocean) and periods (4 a.m.-4 p.m.) were identified by the algorithm as the most important explanatory variables for detecting the presence of tuna. The classification of size categories of tuna aggregations showed a global accuracy of nearly 50 % for both oceans. This study constitutes a milestone towards the use of echosounder buoys data for scientific purposes, including the development of promising fisheries-independent indices of abundance for tropical tunas. |
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English |
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0165-7836 |
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WOS:000539099200018 |
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pas de |
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MARBEC @ isabelle.vidal-ayouba @ |
collection |
2816 |
| Lien permanent pour cet enregistrement |
