Résumé
Functional relationships in marine ecosystems are complex as far as physical and biological parameters are concerned. Improving our understanding of ecosystem functioning requires the ability to observe in situ the interactions between physical and biological features. In this context, the Peruvian anchovy (Engraulis ringens) is an interesting case study as this species supports the highest worldwide landings and is know to present very high populational, distributional and even biological dynamics at different spatio-temporal scales. A specific behavioural ecology survey was performed in November 2004 to study 3D occupation of space by anchovy in Peru. This study was based on an integrated approach. Indeed, using a series of observation tools (Niskin, CTD probes, phyto- and zooplankton sampling, stomach content analysis, echo-sounder, multibeam sonar, birds and mammal observations) we assessed interactions between fish and most of the oceanographic and biotic environmental features possibly driving its behaviour. We could link levels of fish organisation (layer, school, shoal, cluster) according to different oceanographic and biological features: upwelling plume, plankton patches, water mass fronts, predators and others, varying in space and in time, particularly according to the diel cycle. We adapted the basin model framework to propose a conceptual model of environment impact on fish space occupation. Indeed, the small and medium-scale habitat favourability shaped the fish 3D spatial organisation.