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The Northern Mozambique Channel is a treasure of unique oceanography, rich coral reefs, migrating tuna, and whales, bounded by the Comoros, France, Madagascar, Mozambique, Seychelles, and Tanzania. Its living resources are relatively intact and of great importance for food and livelihood security and the developing economies of its surrounding countries. It holds newly discovered natural gas fields of global importance that could fuel unprecedented development pressure, and its 10 million coastal population could grow an order of magnitude by the turn of the century. With these immense pressures against the backdrop of rapid climate change, effective governance across different sectors and among countries will be essential to maintain the region's natural capital and deliver on the promise of sustainable development and “blue economy” subscribed by the surrounding countries. This chapter outlines some of the novel ocean management and governance approaches that may provide the best chance to deliver on a prosperous future.

In order to comply with the different regulations and commitments requesting the presence of scientific observers onboard French purse seiners, and since it is not possible to embark more than one observer during a fishing trip, ORTHONGEL has imagined and implemented since July 2013 a program to facilitate and optimize the boarding of well-trained scientific observers. This voluntary program, called OCUP for "Observateur Commun Unique et Permanent" (Common Permanent Unique Observer) was conducted with the Institute for Research and Development (IRD), Oceanic Développement (OD) and several coastal countries. It was implemented in both Atlantic and Indian Oceans where the fleet adherent to ORTHONGEL is active. This paper describes the methodology of the OCUP program and presents and discusses its main results, focusing on the Atlantic Ocean. In the Atlantic Ocean, 43 scientific observers from 6 African countries have been trained as OCUP. Together with 39 French observers from IRD and OD, 37 of these African scientific observers have covered more than 300 trips until September 1st, 2017 and the coverage of the French fleet has reached 100% since 2015. Since 2013, the OCUP program allows a better coverage of many fishing information such as bycatch or incidental catch and discards data but also provides the boat-owners information on the implementation of best practices aboard their vessels. Lessons learned from this program allow the authors to suggest a few recommendations.

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.

© 2015 Elsevier Ltd.Some of the most important development goals for the countries and territories of the Western and Central Pacific Ocean (WCPO) involve the sustainable management of their fisheries in light of environmental, economic and social uncertainties. The responses of fish populations to variability in the marine environment have implications for decision making processes associated with resource management. There is still considerable uncertainty in estimating the responses of tuna populations to short-to-medium-term variability and longer-term change in the oceanic environment. A workshop was organised to examine how advances in oceanography, fisheries science and fisheries economics could be applied to the tuna fisheries of the WCPO and in doing so identify research priorities to improve understanding relevant to progressing management. Research priorities identified included: (i) improved parameterisation of end to end ecosystem model components, processes and feedbacks through expanded biological observations and incorporation of higher resolution climate models; (ii) development of seasonal and inter-annual forecasting tools enabling management responses to short-term variability in tuna distributions and abundances; (iii) improved understanding of the population dynamics of and the energy transfer efficiencies between food web components; (iv) assessment of the optimal value of access rights and overall fishery value under multiple scenarios of tuna distribution and abundance and influences on decision making by fisheries managers and fleets and (v) development of management strategy evaluation frameworks for utilisation in the implementing and testing of fishery management procedures and to help prioritise research directions and investment. Issues discussed and research priorities identified during the workshop have synergies with other internationally managed fisheries and therefore are applicable to many other fisheries.

Assessing the status of tuna and tuna-like populations for providing management advice requires the analysis of multiple data sets collected by the Contracting Parties and Cooperating non-contracting parties of Tuna Regional Fisheries Management Organizations (tRFMOs) Conventions. Data on the magnitude and composition of landings, discards, and fishing effort are currently managed at basin scale by the Secretariats of the tRFMOs. We have developed a global harmonized database for tuna fisheries data by collating the public domain datasets from ICCAT, IOTC, IATTC and WCPFC. The database covers the period 1919-2014 and is freely accessible online along with a set of open source codes to handle the data. Our objective is to propose services to format and exchange tuna fisheries data and indicators, and promote standards for metadata and data formats to facilitate their through web-based tools. Among others, the expected benefits of the project are the promotion of communication towards tRFMOs and their member States as well as to the general public and the increase of transparency and accessibility to fisheries data sets, indicators, underlying codes, and related expertise.

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.

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.

Assessing the status of tuna and tuna-like populations for providing management advice requires the analysis of multiple data sets collected by the contracting parties and cooperating non-contracting parties of Tuna Regional Fisheries Management Organizations (tRFMOs) Conventions. Data on the magnitude and composition of landings, discards, and sh- ing eort are currently managed at basin scale by the Secretariats of the tRFMOs. Consequently, data formats and reference codes have evolved rather independently despite some links with the FAO Coordinating Work- ing Party on Fishery Statistics. We have developed a global harmonized database for tuna sheries data by collating the public domain datasets (total catch, monthly-spatially aggregated catch and eort, and catch at size) from IOTC, ICCAT, IATTC and WCPFC. The database currently covers the period 1919-2014 and is freely accessible online along with a set of open source codes to handle the data, i.e. transform the data formats, load the standardized data into the database, extract data and compute a suite of indicators (e.g. global maps of catch). The database along with the codes represent the "toolbox".In a previous note ([Taconet et al.]), we have described the general method- ological approach used for the collation and formatting of the data, as well as the bene ts of using standardized data formats and code lists for scien- ti c research and sheries management. In this note, we present the codes available in the toolbox, the services that they oer and how users can access them through various applications. We argue that these methods are likely to bring visibility to the tuna RFMOs public domain datasets, as well as to facilitate their use. Overall, we showcase how the variety of available services and applications enables to reach dierent communities of users that might be interested in accessing tuna fisheries data for various uses and purposes.

Les premières années du gouvernement de Walter Lini ont été marquées par une forte volonté de développer l’exploitation des ressources halieutiques du pays pour renforcer la sécurité alimentaire du pays, réduire sa dépendance économique vis-à-vis de l’extérieur et diversifier l’économie monétaire dans les îles en mettant en exploitation un nouvel espace économique, à l’aide d’une technologie nouvelle, offrant des rendements sans commune mesure avec les pratiques halieutiques traditionnelles. Cette révolution bleue s’est finalement traduite par un échec (cessation d’activités de la spfc à Santo, non-structuration d’une flotte thonière nationale). Quant au programme de développement de la pêche artisanale, il a été victime de son succès initial (trop de groupements de pêche non rentables en raison d’un manque d’assistance technique solide). A very ambitious fisheries development policy, targeting, both pelagic and demersal resources, was conducted during the early years of the Walter Lini government. Its aims were to strengthen the country’s food security and economic self reliance and to diversify the cash economy in the islands. Due to the size of the new economic space and the yields of the new fishing gears, this policy may be related to a blue revolution. This last one has finally resulted in failure. After the closure of the spfc in Santo, Vanuatu authorities have been unable to structure a national tuna fleet or attract foreign investors. The program of artisanal fisheries’development was also a failure after an initial time of sucess. Without strong technical support, too many fishing groups never reached profitability.

Conventional "spaghetti" tags and tags originally designed for "sport fishing" and called Betyp tags, were used during a tuna tagging program conducted on board Dakar baitboats in 1999. With the aim of comparing the recapture rate of both types of tags, additional information obtained from previous tagging trips are used in a Bayesian context to set up an informative prior for conventional tags. We show in this study (1) how to account for the sampling uncertainty in the construction of the Beta prior with a likelihood method, and (2) how a simulation-based alternative can be useful for performing the probability density function of the difference between two posterior recapture rates. On the light of the resulting simulated difference we found that Betyp tags have a very strong negative effect on the return rate of bigeye tuna (−19.6% on average). For skipjack the strength of evidence concerning the decrease in recapture rate due to the implementation of Betyp tags (−3.2%) was supported only at a 10% level. The Bayesian approach is compared with the conventional "frequentist" approach and with a likelihood method allowing for the integration of previous information. The results obtained from different approaches indicate that the choice of the method, as well as the choice of the prior, does not modify the conclusion of the study. Potential causes for explaining the lowest efficiency of Betyp tags are discussed.

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

Since the mid 1990s, drifting Fish Aggregating Devices (dFADS), artificial objects specifically designed to aggregate fish, have become an important mean of catching tropical tunas in the Indian Ocean for the purse seine fleet. In recent years, the massive deployments of dFADs as well as the massive use of tracking GPS and echosounder buoys on dFADs and natural floating objects (logs) have raised serious concerns for tropical tuna stocks but also regarding the possible modifications in ecosystem functioning. However, relatively little remains known on the modalities of dFAD and tracking buoy use by purse seiners. These knowledge gaps render difficult the evaluation of the impacts of fishing practices with dFADs and logs. For the first time, the three French fishing companies operating or having operated in the Indian Ocean provided the GPS buoy tracks of a large proportion of the dFADs and logs monitored by the French fleet. Here, we combine this new source of information with observations of dFADs and logs by observers aboard French and Spanish purse seiners, quarterly French fishing companies orders of buoys, and interviews with purse seine skippers conducted in the port of Victoria. This allows us to identify 4 dFAD and log seasons, to understand the strategies of fishers regarding dFAD and tracking GPS buoy deployment, to extrapolate the total number of dFADs and GPS buoys used by all purse seine fleets and to examine some of the impacts of dFAD use in the Indian Ocean. The results we obtain are a first step for a better assessment and management of the purse seine dFAD fishery.

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.

Recent resolutions of the Indian Ocean Tuna Commission (IOTC) have been implemented to improve scientific knowledge on the effects of drifting fish aggregating devices (DFADs) through increased data collection and reporting. Here, we report information on DFADs collected from three distinct data sources to describe the use of DFADs and buoys by the French PS fleet of the Indian Ocean over the last decade. First, archives of buoy purchase orders during 2002-2014 were provided by fishing companies to give insight into the historical use of DFADs. Data show an homogeneity of the numbers of buoys available to each purse seiner and a steady increase of about 10 buoys per year per vessel, from 50-60 in the early 2000s to 200 in 2013. Second, information derived from satellite transmission data was made available for the period 2010-2013 based on quarterly reports that are produced by buoy supplier companies on a vessel basis. Data show an overall relative stability of the number of French buoys having been used to monitor floating objects (FOBs) during 2010-2013. Each French purse seiner operating in the IO has been monitoring a mean number of 90 FOBs (predominated by DFADs) on a quarterly basis during 2010- 2013, with some variability between vessels and seasons. The total number of FOBs monitored for the French component of the European PS fleet would be around 1,200 in the recent years. Third, an extended version of the PS logbooks has been implemented since January 2013 to include information on DFADs and associated buoys. Although incomplete for some vessels, data collection has been improving over time and several skippers now report a large amount of information on DFADs on an operation basis. This information appears complementary to the two other sources of aggregated data and allows identifying the areas of DFAD deployments for instance.

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.

This paper discusses the skipjack movements observed in the Indian Ocean based on an analysis of fishery data of the 13.128 selected recoveries of tagged skipjack. Its goal is to evaluate the potential geographical heterogeneity of the skipjack population fished in the Indian Ocean. Significant latitudinal & longitudinal movements have been frequently observed; the geographical range of skipjack movements appears to be wide in scale, showing an average distance over 1000 miles between tagging & recovery positions. These distances are showing an increasing trend with time at liberty, and reaching average distances of 1400 miles after 2 years. Recovery data are also showing that skipjack movements are often very fast, for instance reaching average distances over 800 miles after only 1 month at liberty in the Tanzania tagging. Distances covered are the lowest for skipjack tagged in the Maldives and in Seychelles islands and much larger in the Tanzania and Seychelles tagging. these differences are discussed. Because of these fast and extensive movements of skipjack, it can be concluded that its population is highly mobile in the Indian Ocean, but that the mixing rates of individual skipjack that are fished in remote parts of the Indian Ocean are probably low or very low. Based on these results, it is proposed that skipjack indicators and future skipjack stock assessment should be stratified on at least 4 areas, and estimating the mixing rates of skipjack tunas fished in each of these areas.

Nearly 70% of the world's annual tuna harvest, currently 3.2 million tonnes, comes from the Pacific Ocean. Skipjack tuna ( Katsuwonus pelamis ) dominate the catch. Although skipjack are distributed in the surface mixed layer throughout the equatorial and subtropical Pacific, catches are highest in the western equatorial Pacific warm pool, a region characterized by low primary productivity rates1 that has the warmest surface waters of the world's oceans (Fig. 1). Assessments of tuna stocks indicate that recent western Pacific skipjack catches approaching one million tonnes annually are sustainable2. The warm pool, which is fundamental to the El Nino Southern Oscillation (ENSO) and the Earth's climate in general3,4,5, must therefore also provide a habitat capable of supporting this highly productive tuna population. Here we show that apparent spatial shifts in the skipjack population are linked to large zonal displacements of the warm pool that occur during ENSO events5,6. This relationship can be used to predict (several months in advance) the region of highest skipjack abundance, within a fishing ground extending over 6,000 km along the Equator.

En 20011, la flottille de senneurs français de l'océan Atlantique comprenait neuf grands senneurs qui représentaient une capacité de transport totale d'environ 8.000 m3. Les prises totales se sont élevées à environ 37.000 t et se composaient de 58% d'albacore, 33% de listao et de 9% de thon obèse. Après une période de déclin depuis le début des années 90, l'effort de pêche de la flotte augmente depuis 2007 pour atteindre plus de 1.800 jours de recherche en 2011. La hausse de l'effort a été associée à un élargissement des zones de pêche de la flottille au cours de ces dernières années et elle s'est caractérisée par une augmentation du nombre d'opérations. En 2011, plus de 1.900 opérations de pêche ont été réalisées par rapport à environ 800 en 2007. Le pourcentage des opérations réalisées sur des bancs associés à des DCP a augmenté depuis 2007, pour atteindre 41% en 2010 et 34% en 2011, ce qui correspond à 36% de la capture totale de ces dernières années. Aucune tendance n'est apparue clairement dans la série temporelle des taux de capture (exprimée en t par jour de recherche) du thon obèse et du listao dans chaque mode de pêche de la pêcherie, tandis que, depuis le début des années 90, l'albacore capturé dans des bancs libres fait apparaître une tendance ascendante apparente. Le poids moyen de la capture des trois thonidés tropicaux n'a dégagé aucune tendance claire entre 1991 et 2011 à la fois pour les bancs associés à des DCP et les bancs libres, exception faite du thon obèse dont le poids moyen semble augmenter depuis le milieu des années 2000.

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.

In 2012, the European Union and associated flags purse seine fishing fleet of the Indian Ocean was composed of 37 vessels of individual carrying capacity >800 t, which all represented a total carrying capacity of more than 45,000 t. The total cumulated nominal effort was about 9,500 and 7,800 fishing and searching days, respectively. The total number of fishing sets was about 9,000, with about 5,600 realised on FAD-associated schools (i.e. >60%). Overall, the capacity and nominal effort of the fleet have remained stable during the recent years while the total catches have significantly dropped from more than 260,000 t during 2009-2011 to less than 230,000 t in 2012. The decline in catch is mainly explained by a combination of a major decrease in the number of sets per day and catch rates of skipjack on FAD-associated schools, the catch of skipjack per positive set being the lowest observed since 1984, i.e. 15 t set−1. Catch rates of skipjack on free-swimming schools also strongly decreased, which resulted in an overall decrease of skipjack catch by more than 40% between 2009-2011 and 2012. Meanwhile, catch rates of yellowfin on both FAD-associated and free-swimming schools increased in the recent years, resulting in a total catch of yellowfin that increased in 2012 to 130,000 t. The strong reduction in the number of FAD sets resulted in a total catch of bigeye that reached 16,500 t in 2012.

International audience; The imperative to increase seafood supply while dealing with its overfished local stocks has pushed the European Union (EU) and its Member States to fish in the Exclusive Economic Zones of other countries through various types of fishing agreements for decades. Although European public fishing agreements are commented on regularly and considered to be transparent, this is the first global and historical study on the fee regime that governs them. We find that the EU has subsidized these agreements at an average of 75% of their cost (financial contribution agreed upon in the agreements), while private European business interests paid the equivalent of 1.5% of the value of the fish that was eventually landed. This raises questions of fisheries benefit-sharing and resource-use equity that the EU has the potential to address during the nearly completed reform of its Common Fisheries Policy.

The management and conservation of large pelagic fish commonly rely on fisheries data and thus crucially depend on our understanding of the fish response to the fishing gear. Stock assessment of both tropical and temperate tuna strongly leans on the catch statistics derived from pelagic longline fisheries. However, the role of the spatial distribution of catches of tuna and bycatch species over the gear, which can affect the estimated tuna abundance, is still neglected. In this study, we analyzed data obtained from 147 instrumented pelagic longline sets equipped with hook timers and temperature depth recorders to characterize the distribution of hooking contacts and success at a fine temporal and spatial scale. Scientific surveys were carried out in the Central–South Pacific Ocean (French Polynesia), targeting tropical (Thunnus albacares, Thunnus obesus) and temperate (Thunnus alalunga) tuna. Data analysis based on spatial point processes and stochastic modeling demonstrate the presence of spatio-temporal clusters for both hooking contacts and hooking success. The comparative analysis of the observed spatio-temporal patterns for different oceanographic zones revealed the persistent structure of the clusters, suggesting that they are neither related to local environmental conditions nor to the spatial distribution of prey species.

Ce document examine et discute des courbes de croissance de l'albacore (Thunnus albacares) estimées par les scientifiques de l'ICCAT au cours de ces 40 dernières années. Si l'on compare les résultats obtenus de l'analyse des progressions modales, des récupérations des poissons marqués et des lectures des pièces dures aux fins de la détermination de l'âge, on peut conclure que l'albacore suit dans l'océan Atlantique et dans d'autres océans une courbe de croissance complexe multistance, similaire à la croissance humaine, et non un simple modèle de croissance von Bertalanffy. Il est également réaliste de postuler, sur la base de la prise par taille par sexe dans l'Atlantique et d'autres informations, que l'albacore mâle connaît des tailles asymptotiques supérieures à celles des femelles. Cette hypothèse aurait besoin d'être confirmée dans l'Atlantique au moyen du marquage et de la récupération d'albacores adultes par sexe. Le document recommande en outre d'évaluer les changements potentiels dans la croissance de l'albacore susceptibles d'avoir eu lieu au cours de ces 20 dernières années. La réalisation du programme de marquage à grande échelle recommandé en 2010 par le SCRS serait le seul moyen de bien estimer la croissance actuelle de l'albacore et sa variabilité géographique.

In 2011, the French purse seine fishing fleet of the Indian Ocean was composed of 8 large size vessels that represented a total carrying capacity of about 8,000 t. Catches reached a total of 43,000 t and were composed of 50%, 42%, and 8% of yellowfin, skipjack, and bigeye, respectively. After a period of increase during 2006-2008, the fishing effort of the fleet has been decreasing to reach a minimum of 1,800 searching days in 2011. The decrease in effort was associated with a contraction of the fleet fishing grounds in the recent years and mainly characterized by a strong decrease in the number of sets made on free-swimming schools; a total of 1,800 fishing sets being made in 2011 compared to about 4,200 y−1 in the mid-2000s. Hence, the percentage of sets made on FAD-associated schools steadily increased since 2004 to reach more than 65% in 2010-2011, FAD-fishing resulting in 75% of the total catch of the French purse seine fishing fleet in 2011. Species-specific catch rates (in t per searching day) on FAD-associated schools reveal increasing trends over 1981-2011 with high interannual variability while no clear trend is apparent in the time series of catch rates on free-swimming schools. The year 2011 is characterized by a large proportion of yellowfin in the catch on FAD-associated schools that might indicate a good recruitment. For both fishing modes, the mean weight in the catch of the 3 tropical tunas has decreased since the mid-2000s with values in 2011 equal to 7.1 kg, 2.4 kg, and 5.4 kg for yellowfin, skipjack, and bigeye, respectively.

This paper presents the parameter estimation and sensitivity analysis of the APECOSM-E model, which describes the basin scale 3D size-structured population dynamics of the skipjack tuna population in the Indian Ocean under the joint effect of environmental variability and fisheries exploitation. The model is presented in detail in the companion paper ( Dueri et al., 2012 ). A common methodology based on the evaluation of a cost function that combines the negative log-likelihoods of commercial catches and size frequencies is used for both tasks. A Bayesian term representing the a priori probabilities about the model parameters is added to the cost function used for parameter estimation. The partial derivatives of the cost function with respect to the parameters are obtained by deriving the tangent linear code of the model by automatic differentiation of the direct code. A minimization algorithm is used to estimate the parameters related to fisheries and maximise the fitness of the model to the available observations. In a second step, we evaluate the local sensitivity of the non-estimated parameters and identify the model parameters that have an important effect on the output of the model and that would deserve better measurements in order to reduce the level of uncertainty in the model outputs. The comparison between the optimized simulation and the observations allows identifying the model's strengths and limitations, in the perspective of using the model to test scenarios concerning the resilience of the population and the sustainability of its exploitation in the Indian Ocean.

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.

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