Les captures accessoires et les rejets sont inhérents à la pêche depuis toujours mais ce n’est que récemment, avec l’intérêt croissant pour l’approche écosystémique des pêches, qu’une attention particulière est portée à ces sujets aussi bien dans le domaine de la recherche que celui de la gestion des pêches. Le travail présenté dans cette thèse porte sur l’estimation, la caractérisation et la gestion des captures accessoires et des rejets de la pêcherie thonière tropicaleeuropéenne à la senne des océans Atlantique et Indien. La thèse est basée sur les données de livre de bord et celles collectées par les observateurs embarqués à bord des navires de pêche français et espagnols dans le cadre du programme européen de collecte de données DCF (Data Collection Framework). Les prises accessoires et les rejets des océans Atlantique et Indien sont évalués à partir de méthodes statistiques de complexités variables en fonction des questions posées : estimations globales versus locales et/ou par mode de pêche. Une analyse des précisions et biais d’estimation est présentée ainsi qu’une étude comparative des méthodes d’estimation des prises accessoires. Les caractéristiques des prises accessoires et des rejets sont également détaillées. Cette thèse propose un panorama assezcomplet des problématiques liées à la capture accessoire et aux rejets de la pêcherie thonière tropicale européenne à la senne. Elle fait également des propositions pour améliorer la qualité des estimations, réduire les prises accessoires et valoriser les rejets. / Bycatch and discards has always been inherent in fishing but it is only recently, with the growing interest in ecosystem approach to fisheries, that particular attention is paid to these topics both in research and fisheries management.The work presented in this thesis focuses on the estimation, characterization and management of bycatch and discards in the European tropical tuna purse seine fishery of the Atlantic and Indian Oceans. The thesis is based on logbook data andon data collected by observers on board the French and Spanish fishing vessels in the framework of the European data collection programme DCF (Data Collection Framework). Bycatch and discards of Atlantic and Indian Oceans are estimated from statistical methods of various level of complexity according to the questions : global versus local estimations and/or by fishing mode. An analysis of precision and bias in bycatch estimates and a comparative analysis of methods for estimating bycatch are presented. The characteristics of bycatch and discards are also detailed. This thesis proposes a complete overview of issues related to bycatch and discards of the European tropical tuna purse seine fishery. It also makes suggestions to improve the quality of estimates, to reduce bycatch and to valorize the discards.

The Western and Central Pacific Ocean (WCPO) is home to the largest tuna fishery stock in the world. However, Pacific Island members of the Western and Central Pacific Tuna Commission (WCPTC) argue that their share of the economic rent from the tuna catches taken out of the Pacific region is very small, being on average only about 6% of the total net benefit, when compared to the share earned by Distant Water Fishing Nations (DWFNs). Kiribati is one of the Pacific Island Countries (PICs), which relies heavily on its fishery for its economic development and sustainability. Kiribati earns 40% - 50 % of its government revenue from fisheries access fees paid by DWFNs for tuna caught in the the Kiribati EEZ. The Government of Kiribati (GoK) believes that Kiribati could get greater benefit if they develop their own domestic tuna fishery. This study uses Cost-Benefit Analysis (CBA) and SWOT Analysis to investigate whether domestication of the tuna fishery is the right move for Kiribati or not. The CBA reported in this thesis adapted a model developed by Campbell (2004) to investigate and evaluate fisheries policy in Papua New Guinea (PNG). However the model in this thesis is reflective of the situation and case of Kiribati. In analyzing the different options identified in this study, the CBA indicated negative (-) NPV(s) for the medium-sized vessel option and positive (+) NPV(s) for the large-sized vessel option. The SWOT analysis however, complemented the CBA by further investigating the tuna domestication options in the economic, social and business and business environment of Kiribati. The SWOT analysis indicated that the existing situation and business conditions in Kiribati appears to favor the small to medium sized vessel options which are less risky than the large purse seine vessel option.