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In 2017, a total of 12 French vessels operated in the eastern Atlantic Ocean with 1 Bait Boat, 10 Purse Seiner and 1 supply vessel deploying FAD and managing a part of the FAD stock in the water. The total capacity weighted by the months of activity for each vessel is 9 907 t. The total nominal effort in 2017 was of 2794 fishing days and 2335 sets. The total catch of the French component of the EU purse seine fleet of the Atlantic Ocean was 45,730 t, being composed of 56%, 33%, and 8% of yellowfin tuna, skipjack tuna, and bigeye tuna respectively and with 2% of other species.

Ghanaian industrial tuna fisheries data covering the period 2006-2013 were analyzed following guidelines provided during the ICCAT preparatory meeting for the 2015 assessment of bigeye tuna (Thunnus obesus; BET). To account for differences in fishing strategy and quality of data sources available, the fleet was split between a component of large purse seiners and a component composed of baitboats and purse seiners that can collaborate at sea. First, the total Task I was derived from information on landings and logbooks for the first and second fleet components, respectively. Second, the monthly proportion of catch and spatial distribution on a 5°x5° grid were derived from logbook data with some necessary assumptions when data were missing. Third, species composition of the catch was estimated from the size samples collected onboard European purse seiners from fishing sets made on fish aggregating devices based on three processing areas. Bigeye represented about 15% in the ‘offshore’ area while its percentage in the catch was about 7-8% in areas closer to the shore during the same period. Size samples collected by MFRD during 2006-2013 showed that the distribution of bigeye caught by Ghanaian vessels differed from that of European purse seiners on FADs.

Since the mid 1990s, the use of drifting Fish Aggregating Devices (dFADs) by purse seiners, artificial objects specifically designed to aggregate fish, has become an important mean of catching tropical tunas. In recent years, the massive deployments of dFADs, as well as the massive use of tracking devices on dFADs and natural floating objects, such as GPS buoys, have raised serious concerns for tropical tuna stocks, bycatch species and pelagic ecosystem functioning. Despite these concerns, relatively little is known about the modalities of dFAD use, making it difficult to assess and manage the impacts of this fishing practice. The present paper provides an overview of a 4-year research on the use of dFADs by tropical tuna purse seiners in the Western Indian Ocean. Though our primary objective was to derive information on dFAD fisheries from a large variety of quantitative sources of information (GPS buoy positions, onboard observers, logbooks and VMS), a multi-disciplinary approach was adopted throughout our research. Quantitative results (estimates of dFAD use, fishing efficiency and impacts of dFAD use) were discussed with French purse seine skippers during semi-structured interviews to understand their perception of the impacts of dFAD use and to propose adapted management options for tropical tuna purse seine dFAD fisheries. Interviews with French purse seine skippers revealed the existence of a competition between EU purse seine fleets, encouraging the recent increase in the use of dFADs. They underlined the need for a more efficient management of the fishery, including the implementation of catch quotas, a limitation of the capacity of purse seine fleets and a regulation of the use of support vessels.

The drifting Fish Aggregating Device (dFAD) purse seine fishery is complex and fishing effort depends on a multitude of factors. Traditional indices of fishing effort such as searching time are meaningless for this fishery. We composed a comprehensive list of 28 candidate variables that describe the dFAD fishery and used them as predictors of fishing effort in bigeye tuna CPUE standardization of the French purse seiners operating in the Eastern Atlantic Ocean during 2007-2013. We performed variable selection using penalized maximum likelihood in GLM and GLMM frameworks, aiming to improve prediction accuracy and interpretability of the selected models. We applied the Lasso (Least Absolute Shrinkage and Selection Operator) regression models to derive the true parsimonious model, because the number of candidate independent variables is large compared to the number of observations. The penalized model selection process retained explanatory variables such as: the skipper, the vessel, the price of targeted tuna species, the density and spatial distribution of FADs and the number/type of deployed buoys. The inclusion of these predictors in CPUE standardization models provided realistic estimates of uncertainty. We propose the systematic collection of selected explanatory variables and their usage in dFAD related tuna CPUEs standardization in a mixed model framework.

The French purse seine fleet was composed in 2014 of 9 purse seiners of storage capacity >700 t and >60 m length overall, and 1 support vessel of 40 m length overall. The fleet capacity and overall nominal effort have remained stable in the recent years with a total annual number of about 2,000 fishing sets made in 2014, among which 55% on free-swimming schools and 45% on schools associated with fish aggregating devices (FADs). The total number of buoys used for tracking FADs has remained stable during 2010-2014 at around 660 (SD = 100), despite some important variations between vessels and seasons. In 2014, the total landings of the French fleet reached more than 40,000 t and were composed of about 50% yellowfin, 40% skipjack, and less than 10% bigeye. Skipjack predominated in the catch on FAD-associated schools (i.e. 70% in 2014) while large yellowfin predominated in the free-swimming schools catch (i.e. 80% in 2014). Catch rates on FADs have steadily increased to exceed 10 t per searching day in 2014. This increase results from the combination of an increased number of sets on FADs and an increased expected catch per successful set related to increased mean weights of skipjack and yellowfin in the catch.

The reduction of by-catch mortality is an objective of the ecosystem approach to fisheries and a request made by consumers. Elasmobranchs, an important component of the French tropical tuna purse seine fishery by-catch, are currently thrown back into the sea. Fishers interact with various types of elasmobranchs that range widely in size, weight and shape, and could pose various degrees of danger to the crew. A diversity of discarding practices within the fleet were reported, some practices were considered suitable, others needed to be adapted and improved and others simply had to be banned. The majority of the crews were likely to improve their handling practices if they were presented with practical suggestions that were quick and easy. Combining scientific observations and empirical knowledge from skippers and crew, a manual, providing appropriate handling practices to ensure crew safety and increase the odds of survival for released animals has been developed and disseminated. Bringing these good practices onto the decks of fishing vessels should contribute to the reduction of the fishing mortality of some vulnerable species. It would be positively viewed by consumers as an act that reduces fishing's footprint on the environment and promoting animal welfare which would improve the image of fishing industry. Mitigation research is by definition an iterative process and different complementary methods must be carried out at different levels of the fishing process to significantly reduce the mortality of the by-catch.

Within the Ecosystem-based fisheries management framework, we evaluated the changes over time in bycatch species of the European tuna purse-seine fishery operating in the eastern Atlantic Ocean. Bycatch data was collected during two scientific observer programs conducted in the late 1990s and in the late 2000s. Over these two time periods, we compared the temporal trends in bycatch species composition, the probability of occurrence of functional groups per fishing set, the spatio-temporal species richness and the potential impact on several species listed in the red list of the International Union for Conservation of Nature (IUCN). The analyses were performed separately on the two main fishing modes of the fleet, i.e. sets on free-swimming school sets and on fish aggregating devices (FADs). Owing data quality constraints, we did not estimate bycatch rates. Ours results showed that the species composition of sharks caught on FADs decreased over time. The total species richness was higher for FAD sets than for free-swimming school sets (87 vs. 61 species respectively), such difference is common between fishing modes worldwide. For the species catalogued as threatened by the IUCN, in free-swimming schools, 25.5 % of the species caught during first period increased to 30.4 % during second period, while for FAD-fishing the increase was from 28.8 % during first period to 34.9 % in second period. Ours findings suggest that tropical tuna purse-seine fisheries should include ecosystem-based governance of bycatch. Effective tuna management will require a combination of technological improvements for mitigating incidental catch of vulnerable species, best use of byproduct species, regulations in fishing practices and in spatial distribution of fishing effort, and international agreements that, together, can monitor and manage bycatch, reducing the negative fishing effects on the epipelagic ecosystem biodiversity., Sí

Technological advancements can influence both the fishing power of a fleet and the fishing strategies itemploys. To investigate these potential linkages, we examined almost three decades of data (1981–2008)from French tropical tuna purse seiners operating in the eastern Atlantic Ocean. Applying a sequence ofstatistical methods at different temporal and spatial scales, we analyzed two indicators of fishing power(sets per boat-day on fish aggregating devices (FADs) and sets per boat-day on free-swimming schools)each of which represent a distinct fishing mode. Our results show that the increasing modernizationof this fleet has led to increases in both fishing power and the available number of fishing strategies tochoose from. A key output of this analysis was the breakdown of fishing power time series (for each fishingmode) into separate periods of continuous years during which catchability was assumed to be constant,thus identifying regime shifts. This partitioning allowed us to identify when key changes occurred inthe fishery. Changes in FAD-associated fishing were mostly driven by the introduction of radio beacons(early 1990s) which lead to an increase in fishing effort and an expansion of fishing grounds (directeffect) and the implementation of time-area management measures which resulted in a fragmentationof the traditional fishing grounds in the 2000s (indirect effect). During the same period, fishing on free-swimming schools also increased despite the biomass of stocks decreasing and fishing grounds remainingunchanged. This suggests these increases were driven by improvements in fish detection technology (e.g.,bird radars, sonar). These identified increases are not entirely unexpected: indeed it is widely recognizedthat fishing power in the purse seine tuna fishery has increased over time. However, these increases donot necessarily occur linearly. Thus, understanding how fishing power is changing over time (such asdetermining when regime shifts occur) is critical to improving the CPUE standardization procedure intropical tuna purse seine fisheries.

Ce document présente une méthode objective visant à identifier et à évaluer les regroupements des bancs de thons autour des monts sous-marins. La méthode associe la sélection statistique des monts sous-marins actifs sur la base d'une analyse du temps de pêche de la flottille et du schéma de points spatiaux. Le document analyse brièvement les caractéristiques des prises de thonidés pour cinq monts sous-marins sélectionnés par cette méthode dans l'océan Atlantique au titre de la période 1999-2010 pour les flottilles de senneurs et de canneurs français et espagnols. Les prises par km2 sont plus élevées à proximité des monts sous-marins pour les deux flottilles. La composition spécifique change et la proportion des thons obèses augmente dans les captures alors que celle des albacores et des listaos se réduit. Les distributions des fréquences des tailles montrent que les spécimens plus petits sont plus fréquents à proximité des monts sous-marins. Toutefois, ces schémas peuvent varier en fonction des monts sous-marins considérés.

This paper deals with the use of drifting fish aggregating devices (DFADs) in the Indian Ocean and of the potential interest to manage purse seine fisheries through limiting their number. Potential risks associated with a massive use of DFADs are first discussed. Based on new information on the numbers of DFADs released by the French fleet in the 2003-2014 period, this paper estimates the levels and trends of the total numbers of DFADs deployed and active at-sea. It is estimated that the total number of DFADs numbers has been increasing by about 70% since the early 2000s and that they could reach 10,500-14,500 nowadays. A good knowledge of the total numbers of DFADs is urgently needed to better estimate the fishing effort and capacity of purse seine fisheries. Future limitations in the number of DFADs could be a direct and efficient way to reduce fishing effort exerted by purse seiners and their support vessels. Following a precautionary approach, we suggest that IOTC could consider setting a cap on the number of DFADs drifting at-sea and that threshold reference levels could be based on the year 2013, at least to slow down the trend observed in the overall fishing capacity on DFADs. Such measures should be first carefully analysed by an ad hoc IOTC DFAD multidisciplinary working group to ensure their efficient implementation and to allow an improved sustainability of the concerned fisheries.

En 1976, année de l'indépendance du pays, il n'existait aux Seychelles aucune pêche thonière industrielle, et peu d'experts prévoyaient un développement majeur de ces pêcheries. Aujourd'hui Victoria, la capitale, devenue l’un des ports thoniers les plus actifs au monde héberge l'une des plus grosses conserveries de la planète et l'industrie thonière constitue la clef de voûte de l'économie du pays. On ignore souvent que le thon en conserve consommé en Europe provient pour l'essentiel des eaux seychelloises, qui recèlent de très importantes ressources en thons, découvertes lors des campagnes expérimentales de pêche menées par des thoniers senneurs français et espagnols. En l'espace de vingt ans seulement, les retombées socio-économiques ont été considérables, avec création d'emplois et par ailleurs la mise en place d’une flottille palangrière semi-industrielle conduite par des opérateurs locaux. La recherche scientifique a en permanence accompagné ce développement, en assurant un suivi continu de la pêche thonière pour une gestion raisonnée des stocks et la préservation des écosystèmes pélagiques. Fruit d’une importante recherche documentaire et de témoignages recueillis auprès de scientifiques, de patrons thoniers et de personnalités politiques, cet ouvrage retrace les différentes étapes de cette « épopée thonière », jalonnée d’échecs et de réussites. Il nous livre le récit détaillé et vivant de cette tranche d’histoire mal connue et pourtant décisive pour le développement et la diversification économique des Seychelles, et pour les pêcheries thonières de l’océan Indien.

In 2013, the French purse seine fishing fleet of the Indian Ocean was composed of 13 vessels of individual capacity >800 t, which all represented a total carrying capacity >13,000 t of tuna. The total cumulated nominal effort exerted during the year was 3,673 and 3,185 fishing and searching days, respectively. The French purse seiners cumulated a total of more than 2,800 fishing sets, with 1 third made on free-swimming schools (FSC) and 2 third realised on schools associated with fish aggregating devices (FADs). The total annual landings of the principal market tunas by the French purse seine fishing fleet has remained very stable during 2010-2013, with a total of 66,000 t landed in 2013. The landings were composed of more than 55%, 33%, and 10% yellowfin, skipjack, and bigeye, respectively. Catch on FADs increased by 36% between 2012 and 2013 to reach more than 46,000 t. The proportion of yellowin in FAD-catch has strongly increased in the recent years and reached 45% in 2012-2013. The total number of sets per searching day on both fishing modes has been decreasing in the recent years and reached a low value

We used the French purse seine data to examine the trend of skipjack CPUEs for the period 1984-2013. Only sets made on drifting objects (logs and fish aggregating devices –FADs) are used in this analysis. Sensitivity tests were performed to evaluate the effect of the size of the core area in the north equatorial area (0-13N/45’70E) as well as effort minimal thresholds, on CPUE estimates (filtered nominal indices based on the catch per set). No significant effect was noted suggesting that the north equatorial area, as a whole, is a pertinent skipjack core area. A standardization procedure was applied to datasets based on CPUEs aggregated by 1°longitude/0.33° latitude and by month, to which corresponding environmental data such as the depth of the mixed layer, the sea surface anomaly, the speed of the current and the chlorophyll concentration were added. Generalized additive models (GAMs) were used to explore the shape of relationships with fishery-derived and environmental covariates, and undertake transformation in the dataset used by generalized linear models (GLMs). Seven models with various assumptions were tested. They denote a clear skipjack CPUE decline since 2002, with a steeper rate of decline since 2009. We suggest that the massive deployment of FADs during the 1990s and the development of efficient FAD fishing tactics have likely contributed to such decline, as more than 60% of skipjack is caught on FADs. However, environmental fluctuations are also at stake in such decline and notably the chlorophyll concentration which reflects the productivity level at the base of the food chain. The surface chlorophyll concentration has been anomalously low in the Somali Basin since 2006 and this could lead to detrimental foraging conditions for the upper trophic levels, or trigger spatial shift of the population in search of more productive areas. The biological and ecological processes associated to this decline would deserve more research. However, the fact that a sustained CPUE decline for skipjack has been occurring since 2002 could become a concern for the conservation of this stock.

En 2012, la flottille de senneurs français opérant dans l'Atlantique se composait de neuf navires, chacun ayant une capacité de transport > 600 t, représentant dans leur totalité une capacité de transport de 9.000 t. L'effort nominal cumulé total s'élevait à environ 2.500 et à 2.000 jours de pêche et de recherche, respectivement. Le nombre total d'opérations de pêche s'élevait à environ 1.900, à peu près la moitié étant réalisée sur des bancs associés à des dispositifs de concentration des poissons (DCP). Entre 2011 et 2012, la capacité et l'effort nominal de la flottille ont augmenté de plus de 10%, tandis que les prises totales ont diminué de 8%. La chute des captures pourrait s'expliquer par le fait que la flottille n'avait pas accès aux zones de pêche côtières du Gabon, qui représentaient 25% de la capture de la flottille entre 2010 et 2011 (c.-à-d. 8.000-10.000 t). En règle générale, l'année 2012 a été caractérisée par une diminution des opérations de pêche et des prises résultantes sur bancs libres, ce qui a été en partie compensé par l'augmentation des prises sous DCP. Par conséquent, la prise totale de listao et de thon obèse est demeurée stable entre 2010 et 2012, c.-à-d. à environ 12.600 t et 3.300 t, respectivement, tandis que la prise d'albacore a baissé de 15% entre 2011 et 2012 pour atteindre environ 18.000 t. La baisse des prises d'albacore était due à la diminution du nombre d'opérations par jour de recherche sur bancs libres tandis que la capture par opération positive est demeurée inchangée pour les deux modes de pêche en 2012, c.-à-d. 20,8 t opération -1 pour la pêche en bancs libres et 3,4 t opération-1 pour la pêche sous DCP. Pour le listao, la prise par opération positive dans la pêcherie opérant sous DCP a chuté de 13,5% entre 2011 et 2012, mais elle est demeurée à un niveau de 14 t opération -1 similaire à la moyenne observée entre 2009 et 2011. En revanche, les captures de listao par opération positive en bancs libres ont diminué progressivement entre 1991 et 2012, pour atteindre un minimum de 0,56 t opération-en 2012 en rapport avec l'absence de la pêche dans la zone de Cap Lopez où les gros listaos sont généralement capturés.

Indices of CPUE are presented for skipjack tuna (Katsuwonus pelamis) for the Indian Ocean over the period 1980-2013. The analysis was initiated under the framework of the E.U. research project CECOFAD, whose objectives are to enhance our understanding of fishing effort units and improve the accuracy of purse-seine CPUE estimates. Skipjack stock assessments mainly depend on abundance indices derived from purse-seine fleets, thus standardisation of purse seiner CPUEs for this species is a priority. We follow a CPUE definition framework where three different types of CPUE are calculated to describe trends in number of schools, school detectability and catchability and school size. CPUE standardization is typically achieved with the development of GLM models; these estimates are often biased because the range of the fishing area changes from one year to the next. We compare CPUE trends derived from conventional GLMs with trends based on GLMMs, where the spatial explanatory variables are treated as a random effect. According to a definition, a variable is random when it constitutes only a part of the entire population: spatial variables can be considered random since each year fishing vessels sample only a part of the historically fished area. Exploratory analyses revealed issues of heterogeneity and autocorrelation, supporting the use of mixed models and the shift towards a Bayesian approach to CPUE standardization modeling. Our analysis uses fishing sets targeting free swimming tuna schools for the French purse seiners operating in the western Indian Ocean. Future work will address the problem of accounting for the major changes in purse seine fishing strategies and the implementation of new technology on board (mainly the use of FAD technology) under a Bayesian framework.

Ce document présente une méthode objective visant à identifier et à évaluer les regroupements des bancs de thons autour des monts sous-marins. La méthode associe la sélection statistique des monts sous-marins actifs sur la base d'une analyse du temps de pêche de la flottille et du schéma de points spatiaux. Le document analyse brièvement les caractéristiques des prises de thonidés pour cinq monts sous-marins sélectionnés par cette méthode dans l'océan Atlantique au titre de la période 1999-2010 pour les flottilles de senneurs et de canneurs français et espagnols. Les prises par km2 sont plus élevées à proximité des monts sous-marins pour les deux flottilles. La composition spécifique change et la proportion des thons obèses augmente dans les captures alors que celle des albacores et des listaos se réduit. Les distributions des fréquences des tailles montrent que les spécimens plus petits sont plus fréquents à proximité des monts sous-marins. Toutefois, ces schémas peuvent varier en fonction des monts sous-marins considérés.

This study provides a historical overview of the use of drifting fish aggregating devices (DFADs) in purse seine fisheries since the early 1990s, using global tuna fisheries datasets from the four tuna Regional Fisheries Management Organizations (RFMOs). Tropical tuna purse seine fisheries typically target large yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tunas on free-swimming schools and skipjack (Katsuwonus pelamis )a nd juveniles of yellowfin and bigeye associated with drifting objects. DFADs have enabled global skipjack catches to markedly increase, and have also introduced major scientific issues for all tuna-RFMOs. In particular, they have strongly modified the fishing strategies of purse seiners that fish on a combination of free-swimming and DFAD-associated schools. Consequently, the cumulated search time traditionally used to quantify nominal fishing effort to assess the status of tuna stocks is inconsistent and cannot be used to derive time series of abundance indices from catch-per-unit of-effort (CPUE). In addition, the lack of information available on the construction, deployment, and use of DFADs has prevented effective monitoring of the fishing pressure over the last two decades exerted by purse seine fleets using this fishing mode. Juveniles of tropical tunas represent a substantial proportion of purse seine catch on DFADs in the three oceans, which has raised particular concern for some bigeye stocks that have been subject to overfishing in the past. Catches of juvenile tunas by DFAD fishing may also result in a decrease in recruitment for fisheries that target adult tunas such as longliners. In addition, some demographic parameters of tunas and other species associated with DFADs may be affected by the resultant habitat modification arising from the widespread deployment of DFADs. Evidence in the literature and provided by the ratio-estimator method suggest that fishing DFAD-associated schools may result in about 100 000 t of bycatch and discards annually. In addition, there is further potential for ghost fishing related mortality of sensitive species such as marine turtles and pelagic sharks. In this context and following a precautionary approach, we finally discuss the increasing need for all tuna-RFMOs to reduce, or at least monitor and control, the use of DFADs to mitigate their adverse effects not only on yellowfin and bigeye stocks but also on open-ocean ecosystems.

Les strategies de peche, developpees par les capitaines des thoniers senneurs venezueliens dans la mer des Caraibes, reposent sur la recherche d'indices visuels indiquant la presence de thons a la surface de l'ocean. Une fois que la detection est realisee, le senneur peut choisir la tactique qui consiste a demander l'aide d'un thonier canneur (peche a l'appât vivant) afin d'augmenter le taux de reussite d'un coup de senne. Pour prendre en compte la variabilite de differents facteurs, comme la saison, les indices de detection associes aux bancs, l'aide du thonier canneur, les especes de thons et le poids moyen des poissons presents dans le banc, les probabilites de realisation de certains evenements sont estimees a l'aide de la modelisation Logit, issue de modeles Log-lineaires. Les probabilites de capturer des bancs de gros individus sont maximales lorsque l'albacore est l'espece dominante et que la peche a lieu sur banc libre ou sur requin-baleine; cet effet est d'autant plus marque en saison seche. En revanche, si le listao est l'espece dominante, la probabilite de capturer des gros individus est faible, en particulier lorsque la peche est realisee sur des baleines. Les resultats de cette modelisation sont integres dans un arbre de decision. Si on retient le critere de l'esperance mathematique des gains potentiels, l'aide du thonier canneur ne semble pas etre la meilleure des tactiques possibles. Pourtant son impact est positif sur le taux de reussite d'un coup de senne, puisque le pourcentage de calees positives passe de 58 % sans aide a 85 % avec aide. L'efficacite de cette aide depend du type d'association rencontre. Elle augmente lorsqu'il s'agit de bancs libres ou en association avec des baleines, mais diminue lorsque le banc est associe a un requin-baleine.Une simulation par la methode de Monte Carlo montre que, malgre l'absence de cette aide, quelques gains importants peuvent etre realises lorsque l'objet flottant associe est une baleine. En consequence, le choix tactique qui consiste a demander l'aide d'un thonier canneur et qui est plus frequent chez les petits et moyens scnncurs que chez les grandes unites, pourrait traduire une attitude de prudence face au risque, sans ecarter certaines contraintes physiques de ces senneurs comme leur vitesse. Si on la compare avec d'autres zones de peche thoniere, la mer des Caraibes se caracterise par une forte proportion de coups de senne faites sur requins-baleines (37 % des coups) et sur baleines (24 %). En contrepartie, le nombre de coups de senne faits sur des epaves flottantes est tress faible. Ceci pourrait etre lie a la nature des courants marins qui entraineraient ces epaves en dehors de la zone de peche des senneurs venezueliens. La similitude des comportements adoptes face au risque, dans des milicux tres differents comme la peche et l'agriculture, est discutee brievement.

Amandè, M. J., Chassot, E., Chavance, P., Murua, H., Delgado de Molina, A., and Bez, N. 2012. Precision in bycatch estimates: the case of tuna purse-seine fisheries in the Indian Ocean. – ICES Journal of Marine Science, 69: . Estimating bycatch, i.e. the incidental catch of non-target marine animals and undersized individuals of target species, by raising observer data to the whole fishery is routine practice. The annual bycatch of the European tropical tuna purse-seine fishery over the period 2003–2009 was estimated at 11 590 t [95% confidence interval: (8165–15 818 t)], corresponding to 4.7% of the tuna landings. An analysis of the variability in the precision of this estimate, based on generalized linear models and Monte Carlo simulations, showed that the current sampling coverage of the tropical tuna fishery observer programme, which is 4.6% of the fishing trips, resulted in large uncertainties in bycatch estimates by species, i.e. none of the estimates have a relative root mean square error smaller than 50%. Although the overall magnitude of bycatch of the fishery appeared to be small, the current sampling coverage was insufficient to give any reliable estimate for low-occurring species, such as marine turtles, some oceanic pelagic sharks, and some billfishes. Increasing the sampling coverage would likely improve bycatch estimates. Simulation outputs were produced to help define (i) trade-offs between the priority species to be monitored, (ii) the estimation precision, (iii) expected accuracy, and (iv) the associated sampling costs.

Time-area closures have become a frequently used tool to control fishing effort and protect feeding and spawning areas. However, because time-area closure strata are mainly based on biological and ecological considerations, and do not accounts for fishermen’s behavior-at-sea, this type of regulation tool may not entirely achieve its objectives. With the aim of comparing the impact of two different time-area regulations: (1) a moratorium on Fish Aggregating Devices (FAD) sets (1997–2005) and (2) a no-take area for surface fleets (2005–2010) on the dynamics of the European (EU) tuna purse seine fleet operating in the eastern tropical Atlantic, several fishery indicators were evaluated through a Before-After, Control-Impact (BACI) approach. The results showed that prior to any regulation, the fleet used to be concentrated within the Gulf of Guinea area. During the first years of the moratorium on FAD (from November to January within a large region in the eastern Atlantic) there was a movement towards outside the protected area, increasing the total sets on FAD (restricted fishing activity). In general, this moratorium fulfilled its objectives; however, it was not respected during the last years of this regulation. The no-take time-area closure restricted all tuna catches for the surface fisheries but only in November and within a small area (i.e., the Picolo zone). As a result, there was an increase in activities on free schools outside the no-take area. Our findings suggest the use of some simple fishery indicators to understand fleet dynamics as a complement of ecological information before implementing new time area closures. Furthermore, since tunas are highly mobile species, anticipating the possible re-allocation of effort of purse seiners to adjacent areas in response to the spatial regulation is required to design different candidate time-area closures and to evaluate their effectiveness to protect juvenile tunas.

This document presents a summary of the statistics of French, Spanish, Italian, Seychelles and EU related NEI purse seine fleets fishing in the Indian Ocean since 1981: effort, catch by species and fishing type (log and free swimming schools), catch per unit of effort, sampling and mean weights for the main species. Since 2002, data from the European fleet (France and Spain) are collected within the framework of the EU “Data Collection Regulation” (DCR, Reg. 1543/2000 and 1639/2001), followed in 2008 by the “Community framework for the collection, management and use of data in the fisheries sector and support for scientific advice regarding the Common Fisheries Policy” (DCF, Reg 199/2008 and 665/2008). Data from other fleets are collected by SFA (Seychelles Fishing Authority). Data processing (species composition and size distribution) is done collectively for the whole fishery.

In the lack of direct estimate of tuna abundance, the French tropical tuna fleet of purse-seiners provides a way to monitor the tuna stocks particularly through the calculation of Catch per Unit of Effort (CPUE). The objective of this study was to analyze the individual track of purse seiners with the aim to identify which part of the searching behaviour should be used to perform the fishing effort. In this context, Vessel Monitoring Systems (VMS) data are useful to analyse the different fishing activities of a purse seiner at a small scale (i.e.. stop, track and cruise), generally embedded into the concept of fishing effort. A state-space model (run in a Bayesian framework) was applied to speeds and turning angles from Vessel Monitoring Systems (VMS) data, to identify the different “states” of the fishing behaviour of a purse seiner over a fishing trip. Then a threshold was fitted to distinguish the activities “fishing” and “stop” without fishing (from the “still” state), “tracking” (from “meander”), and “cruising” (from “straight”). On a subset of VMS data corresponding to observers' data, some differences of fishing efforts between fishing on free-swimming schools and schools associated with FAD (Fish Aggregating Devices) are highlighted.

This paper shows the difficulty to visually to illustrate the variability of the species composition of sampled sets landed by purse seiners in the Indian and Atlantic Oceans. When large numbers of sets have been sampled during the last 30 years, it is still quite difficult to visualize the heterogeneity of their species compositions. This paper proposes to use the ternary plots proposed by De Finetti to solve this problem. These ternary plots have been drawn as examples on the Free and FAD schools sets sampled in the Indian and Atlantic oceans during the 2002-2008 period. These ternary plots have been drawn as examples using 3 different plotting methods, but other alternate improved methods could also be envisaged following the discussion of this working document

The document describes the fishing activities of the French purse seiners targeting tropical tunas, i.e. Thunnus albacares, Katsuwonus pelamis, and Thunnus obesus in the Indian Ocean during 1991-2009. The catch time series of the fleet over the period 2001-2009 has been updated following a change in the spatial stratification used in the multispecies sampling and a few modifications in data processing. Information is provided on fishing effort (fishing days, searching days, and fishing sets), catch, catch rates, and mean weights for the major tropical tuna species. Two major fishing modes are considered for the fishery: log-associated and free swimming schools.

Working Group ICCAT July 2008; Florianopolis, Brasil; The PROCEAN (PRoduction Catch / Effort ANalysis) model is a multi-fleet biomass dynamic model developed in a Bayesian framework to conduct stock assessments based on catch and effort time series data. PROCEAN was applied to the eastern component of the Atlantic skipjack (Katsuwonus pelamis) to assess the current status of the stock and provide reference points to fishery managers. Data included 8 time series of catch and effort data spanning from 1969 to 2006 and mostly standardised based on generalized linear modelling techniques. Informative priors and constraints for some parameters were used to allow the model to converge. Model fits were generally good but indicated increasing trends in the residuals for some fishing fleets. Results suggested that the eastern Atlantic skipjack stock would be underexploited, with a biomass in 2006 equal to 1.8 times the biomass at the maximum sustainable yield (MSY) and a fishing mortality in 2006 equal to 30% of the fishing mortality at MSY (FMSY). A sensitivity analysis performed to account for uncertainty in some input parameters showed that FMSY estimates were robust to parameter changes while MSY estimates were sensitive to the prior distribution for MSY. Based on the different model runs, the MSY was estimated to be comprised between 152,000 and 185,000 t. The use of random walks on catchability was useful for tracking changes in catchability and associated increasing fishing power for some baitboat fishing fleets targeting skipjack.

This document presents a standardized index update of adult yellowfin (>30 kg) of tropical purse seine fleets in the Atlantic Ocean from 1980 to 2006. The data used were taken from spear fishing logbooks and detailed information of the fleet. The standardization has been carried out by generalized linear models (GLM) using the delta model. The standardized indices are obtained from the GLM model estimations: one is calculated from the least squares means (LSMeans) and another from the annual averages of the adjusted values. The variability of the latter is lower. Therefore, in this case, it is a more adequate index to be used in assessment models. The year, country, category, age of vessel and catches of skipjack tuna, which is the other target species of these fleets, were considered as explanatory variables.

An increasing proportion of landings by tuna purse seine fishing vessels are taken around drifting Fish Aggregating Devices (FADs). Although these FADs and their use by the fishing industry to capture tropical tuna have been well documented, operative tools to collect data around them are now required. Acoustic, video, photographic and visual data were collected on fish aggregations around drifting FADs in offshore waters of the western Indian Ocean. Multibeam sonars, multifrequency echosounders, pole-mounted digital video camera and an automated 360° rotating digital photographic camera were deployed from a vessel in the vicinity of FADs, and their observation capability evaluated with underwater visual census made by divers. Two prototypes of instrumented buoys equipped with scanning sonar were tested providing positive results on their feasibility and operability as pelagic observatory. Acoustics methods combined with digital underwater video represent interesting possibilities to remotely study the composition and behaviour of these fish aggregations. The acoustic methods allowed the accurate description of the spatial organisation and dynamics of individual fishes, schools and biotic scattering layers around the FAD, but species identification was difficult. In situ visual, photographic and video observations systems permitted species identification within a range of 0 to ~ 25 m. However, scuba divers observations were more efficient compared to the photographic and video cameras at detecting the presence of certain fish species around FADs. Obviously both methods are complementary, since the acoustic methods could not identify most fish species and could not detect the presence of small fishes found less than 5 meters under the FAD. These fishes represent a small part of the overall biomass of fish aggregations but they are part of the biodiversity of pelagic ecosystems and may play a major role in ecological processes associated with FADs. The opportunity to incorporate observation tools into the development of future autonomous instrumented drifting buoys for remotely monitoring fish diversity and abundance in the pelagic ecosystems is presented. The perspective of autonomously collecting large amounts of basic information useful for ecological and fisheries studies in an ecosystemic approach for open sea or coastal pelagic environment is emphasized. Keywords: Visual and video Fish census / Acoustics / Buoy system / Pelagic species / Monitoring / Observatory.

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