Résumé
From 2002 to 2004, four scientific cruises were conducted by the Institut de Recherche pour le Developpement (IRD) in the Mozambique Channel (Western Indian Ocean), in order to study the pelagic habitat of large top predators such as tuna and tuna-like species. Acoustic data were recorded to study the spatial and temporal distribution of plankton layers and micronekton aggregations. Sea temperature, salinity, dissolved oxygen and fluorimetry profiles (not available for all the cruises) were carried out from the surface to 300 m using a Sea-Bird CTD. Sea water samples at different depth levels were filtered to characterize the photosynthetic pigments, and nutrients were analysed. Satellite data (ocean colour and altimetry) provided complementary information at a larger scale. In this study, we analyse the aggregative behaviour of schools and the dynamics of the scattering layers in relation with abiotic parameters at different spatial scales. We underlined the importance of meso-scale dynamics for the productivity in these areas (i.e., occurrence of cyclonic eddies in the Mozambique Channel) and the importance of the deep maximum chlorophyll for the distribution of the micronekton.