Résumé
Environmental changes and human activities can have strong impacts on biodiversity and ecosystem functioning. In this context, there is now a growing importance to consider modifications in the functional diversity of species communities in addition to the traditional quantification of changes in species diversity and composition. In spite of their trophic and economic importance in open-sea ecosystems, the functional diversity of large predatory fishes such as tunas, swordfish, billfishes and sharks is still poorly documented. In this work, we investigated the spatio-temporal variations in the functional diversity of fish predators in the western Indian Ocean during eight years. Fishes were caught by longliners during scientific surveys performed between 2000 and 2008 in the Seychelles area and in the Mozambique Channel. A total of 26 species were identified and 20 functional traits were quantified to describe four main functions: food acquisition, locomotion, social behaviour and reproduction. Recent methodological advances, including both indices and multivariate analyses, were performed to quantify on these data complementary facets of functional diversity. These methodological approaches allowed an original investigation of functional diversity variability of large predatory fishes in the Indian Ocean, and potential impacts of environmental changes and human activities are discussed.