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Drifting Fish Aggregating Devices of the Atlantic and Indian Oceans : Modalities of Use, Fishing Efficiency and Potential Management Alexandra Maufroy

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Drifting Fish Aggregating Devices of the Atlantic and Indian Oceans : Modalities of Use, Fishing Efficiency and Potential Management Alexandra Maufroy Drifting Fish Aggregating Devices of the Atlantic and Indian Oceans : modalities of use, fishing efficiency and potential management Alexandra Maufroy To cite this version: Alexandra Maufroy. Drifting Fish Aggregating Devices of the Atlantic and Indian Oceans : modalities of use, fishing efficiency and potential management. Animal biology. Université Montpellier, 2016. English. NNT : 2016MONTT150. tel-01663770 HAL Id: tel-01663770 https://tel.archives-ouvertes.fr/tel-01663770 Submitted on 14 Dec 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. THESE Pour obtenir le grade de Docteur Délivré par l’Université de Montpellier Préparée au sein de l’école doctorale GAIA Et de l’unité de recherche UMR MARBEC Spécialité EFSA Présentée par: Alexandra MAUFROY Drifting Fish Aggregating Devices of the Atlantic and Indian Oceans: modalities of use, fishing efficiency and potential management SoutenueSoutenance le 30prévue Juin le2016 30 Juindevant devant le jury le composéjury: de: Mme Jocelyne FERRARIS, IRD, UMR Entropie, Rapporteur M. Paul MARCHAL, Ifremer Centre Manche Mer du Nord, Rapporteur M. Didier GASCUEL, Agrocampus Ouest Rennes, Examinateur M. Roger PRADEL, CEFE - CNRS, Examinateur M. Nicolas BEZ, IRD - UMR MARBEC, Directeur de thèse M. Emmanuel Chassot, IRD - UMR MARBEC, Co-Directeur de thèse M. David M. KAPLAN, VIMS (USA), Invité A Tom. Sans qui cette thèse n’existerait pas. Mais sans qui plus rien n’a de sens. 5 Abstract 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, by - catch species and pelagic ecosystem functioning. Despite these concerns, relatively little is known about the modalities of GPS buoy tracked objects use, making it difficult to assess and manage of the impacts of this fishing practice. To fill these knowledge gaps, we have analyzed GPS buoy tracks provided by the three French fishing companies operating in the Atlantic and the Indian Oceans, representing a large proportion of the floating objects monitored by the French fleet. These data were combined with multiple sources of information: logbook data, Vessel Monitoring System (VMS) tracks of French purse seiners, information on support vessels and Local Ecological Knowledge (LEK) of purse seine skippers to describe GPS buoy de - ployment strategies, estimate the total number of GPS buoy equipped dFADs used in the Atlantic and Indian Oceans, measure the contribution of strategies with FOBs and support vessels to the fishing efficiency of tropical tuna purse seiners, identify potential damages caused by lost dFADs and finally to propose mana - gement options for tropical tuna purse seine FOB fisheries. Results indicate clear seasonal patterns of GPS buoy deployment in the two oceans, a rapid expansion in the use of dFADs over the last 7 years with an increase of 4.2 times in the Indian Ocean and 7.0 times in the Atlantic Ocean, possible damages to fragile coastal ecosystems with 10% of GPS buoy tracks ending with a beaching event and an increased efficiency of tropical tuna purse seine fleets from 3.9% to 18.8% in the Atlantic Ocean over 2003-2014 and from 10.7% to 26.3% in the Indian Ocean. Interviews with purse seine skippers 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. These results represent a first step towards better assessment and management of purse seine FOB fisheries. keywords: tropical tunas, fishing effort, pelagic ecosystems, Atlantic Ocean, Indian Ocean, Fish Ag - gregating Devices 7 Résumé Depuis le milieu des années 1990, l’utilisation de Dispositifs de Concentration de Poissons (DCP), des objets artificiels spécifiquement mis à l’eau pour agréger des bancs de poissons, est devenue de plus en plus importante pour la pêche au thon tropical à la senne. Cette utilisation massive des DCP, qui s’accompagne d’une utilisation massive de dispositifs de suivi comme les balises GPS et les balises échosondeurs, est aujourd’hui source d’inquiétude pour les stocks de thons, les prises accessoires mais aussi pour le fonction - nement des écosystèmes pélagiques. Cependant, les modalités d’utilisation des DCP et des balises GPS qui servent à les suivre restent mal connues, ce qui complique considérablement l’évaluation et la gestion des impacts de ces pratiques de pêche. Afin d’améliorer les connaissances actuelles de la pêcherie, les positions des balises GPS utilisées par les 3 armements français dans les océans Atlantique et Indien, constituant une part significative des DCP utilisés dans ces deux océans, ont été analysées. Ces données ont été combinées avec des multiples sources d’information : les livres de bord, les trajectoires VMS des senneurs français ainsi que des entretiens avec les patrons français. Elles nous permettent de mieux comprendre les stratégies de mise à l’eau des DCP et des balises, d’estimer le nombre d’objets flottants utilisés par les flottes de senneurs dans les océans Atlantique et Indien, de mesurer la contribution des DCP et des navires auxiliaires à l’effica - cité de pêche des senneurs, d’identifier des destructions potentielles d’habitats par les DCP échoués et pour finir de proposer des solutions de gestion pour la pêcherie. Les résultats montrent une importante saison - nalité dans les mises à l’eau des deux océans, une croissance rapide du nombre de balises GPS au cours des 7 dernières années puisqu’elle est multipliée par 4.2 dans l’Océan Indien et 7 dans l’Océan Atlantique, des dommages possibles causés à des écosystèmes côtiers fragiles avec une probabilité d’échouage de l’ordre de 10% et finalement une augmentation de l’efficacité de pêche entre 2003 et 2014 de l’ordre de 3.8- 18.8% dans l’Océan Atlantique et 10.7%-26.3% dans l’Océan Indien. Les entretiens avec les capitaines des senneurs soulignent la nécessité d’une gestion plus efficace de la pêcherie, avec entre autres l’instauration de quotas, une régulation de la capacité de la flotte de senneurs et un meilleur suivi des navires auxiliaires. Les résultats obtenus constituent les premières étapes nécessaires à une meilleure gestion de la pêche sous objet flottant. mots clés: thons tropicaux, effort de pêche, écosystèmes pélagiques, Océan Atlantique, Océan Indien, Dispositifs de Concentration de Poissons 9 Remerciements Cette étude a été financée par France Filière Pêche (http://www.francefilierepeche.fr/) et a bénéficié d’une aide du projet AMPED (Aires Marines Protégées pour Espèces qui se Déplacent beaucoup, www.amped.ird. fr), financé par l’Agence Nationale de la Recherche (ANR) dans le cadre du programme SYSTERRA ainsi que d’une aide de l’Observatoire Thonier. Une partie des questions abordées dans cette thèse s’inscrit dans le projet CEcoFAD (Catch, Effort, and eCOsystem impacts of FAD-fishing). Je tiens tout d’abord à remercier mes directeurs de thèse Emmanuel Chassot, David Kaplan et Nicolas Bez. A chacun de vous, merci de m’avoir donné la chance de découvrir cette pêcherie fascinante. Entre dé - couvertes et rebondissements, la route n’a pas été facile mais vous avez su tour à tour me guider, m’accom - pagner, bousculer mes certitudes parfois, tout en me laissant la liberté d’explorer des pistes qui me tenaient à cœur. J’ai beaucoup appris de ces quatre années passées avec vous. Je souhaite aussi remercier les membres de l’Observatoire Thonier, pas seulement pour les données sans lesquelles cette thèse n’existerait pas mais aussi pour leur aide et pour leur soutien. En particulier, je remercie Laurent Floch pour son aide précieuse tout au long de ce travail, le temps passé à résoudre les dif - ficultés techniques et à préparer les données. Je remercie également Daniel Gaertner pour sa bienveillance et son aide précieuse pour démêler les inextricables problèmes d’effort de pêche, ainsi qu’Alain Fonteneau et Francis Marsac pour leurs bons conseils et leur relecture de mon dernier chapitre en un temps record. Je remercie Orthongel (Organisation des producteurs de thon congelé et surgelé, http://orthongel.fr) qui a mis à la disposition de l’IRD les données de position des balises GPS utilisées par les thoniers senneurs français pour suivre leurs objets flottants. Je remercie les instituts Espagnols AZTI (http://www.azti.es/) et IEO (http://www.ieo.es) qui ont mis à notre disposition les données observateurs collectées à bord des sen - neurs Espagnols ainsi que les données des livres de bord. Je remercie la SFA aux Seychelles pour m’avoir accueillie à deux reprises et pour les informations recueillies sur les navires auxiliaires. Je remercie chacun des patrons Français ou Espagnols qui m’ont accordé leur temps et leur confiance, pour certains d’entre eux à deux reprises. Vous m’avez aidé à transformer des chiffres en histoires et à don - ner un autre sens à mon travail, j’espère que les résultats sont à la hauteur de ce que vous m’avez apporté. Je souhaite également remercier toutes les autres personnes avec lesquelles j’ai pu échanger au cours de ce travail (armements, ONG, pêcheurs locaux aux Seychelles, gestionnaires, conserverie) et qui m’ont aidé à y voir plus clair.
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