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Statistics of French purse seine fishing fleet targeting tropical tunas in the Indian Ocean







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    Statistics of the purse seine fleets of France’s overseas territories targeting tropical tunas in the Indian Ocean 2013
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    Statistical data for the France’s Overseas Territories (FRAT) purse seine fleet have been collected by the “Institut de Recherche pour le D ?eveloppement” (IRD) since 2001. Purse seiners registered in the harbour of Dzaoudzi, Mayotte, belong to the EU purse seine fleet of the Indian Ocean and data collection and processing are similar to the ones used for the French component of the fleet. Tropical tu purse seiners target yellowfin (Thunnus albacares), skipjack (Katsuwonus pelamis), and bigeye t u (Thunnus obe- sus) through two major fishing modes that result in different species and size composition of the catch: fish-aggregating device-associated (FAD) and free-swimming schools (FSC). Here, the acronym ”FAD” encompasses any type of drifting floating object to which tu schools can associate. This definition includes ”tural” objects (e.g. logs, palm branches) and anthropogenic floating objects, such as man- made bamboo rafts equipped with radio-range beacons, satellite transmitters and scanning sors. The fleet activities are described through a suite of fisheries indicators that provide information on fishing capacity and effort, catch, and catch rates for the 3 principal market tropical tus, with a particular focus on the year 2012.
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    Global spatio-temporal patterns in tropical tuna purse seine fisheries on drifting fish aggregating devices (DFADs): Taking a historical perspective to inform current challenges 2013
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    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 tu fisheries datasets from the four tu Regiol Fisheries Magement Organizations (RFMOs). Tropical tu purse seine fisheries typically target large yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tus on free-swimming schools and skipjack (Katsuwonus pelamis) and juveniles of yellowfin and bigeye associated with drifting objects. DFA Ds have ebled global skipjack catches to markedly increase, and have also introduced major scientific issues for all tu-RFMOs. In particular, they have strongly modified the fishing strategies of purse seiners that fish on a combition of free-swimming and DFAD-associated schools. Consequently, the cumulated search time traditiolly used to quantify nomil fishing effort to assess the status of tu stocks is inconsistent and cannot be used to derive time series of abundance indices from catch-per-un it 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 tus 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 tus by DFAD fishing may also result in a decrease in recruitment for fisheries that target adult tus such as longliners. In addition, some demographic parameters of tus 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 additi on, 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 precautiory approach, we filly discuss the increasing need for all tu-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.
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    A critique of the ecosystem impacts of drifting and anchored FADs use by purse-seine tuna fisheries in the Westernand Central Pacific Ocean 2013
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    In the Western and Central Pacific Ocean (WCPO), which accounts for over half of world tu production, purse seine effort and catch on floating objects have increased significantly due to a rapid increase in the use of fixed and free-floating fish aggregation devices (FADs). FAD fishing has had an impact on the current status of the stocks of the three main target tus in the equatorial WCPO, skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (T. obesus). FADs have been shown to influence the behaviour and movement patterns of the three tu species with the juveniles of each species occupying shallower habitats when associated with FADs. Aggregation of tus around drifting objects increases their vulnerability to purse seine gear, particularly for juvenile and small size classes. Further to the impacts on the target stocks, the use of FADs has increased the vulnerability of other fishes to the purse seine method, including some shark and billfish species. Given the con cern over FAD-related fishing effort on target and bycatch species, there is a need to understand how FAD use affects target and bycatch stocks. Science needs to better support magement decisions are highlighted including the need to identify the magnitude of broader community-level affects.

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