Stratégie de reproduction des petits poissons pélagiques dans les zones d'upwelling : Une approche par modélisation individu-centrée appliquée aux systèmes de courants de Humboldt et des Canaries

Eastern boundaries upwelling systems are very productive and sustain the largest fisheries in the world. Biomass in these systems is dominated by small pelagic fish, mainly sardine and anchovy species. Their population dynamics displays a very high abundance variability related to the upwelling physical variability. Understanding the linkage between the environmental fluctuations and the small pelagic fish recruitment in upwelling systems is a key issue for fisheries sciences. In this context, an individual-based model (IBM) approach is proposed to study the early life history of small pelagic fish. Hydrodynamics simulations are used as input in the IBM to represent the environmental conditions experienced by fish eggs and larvae. The results give information about ichthyoplankton survival rates as a function of spawning date and area. The effects of lethal temperature, egg buoyancy and vertical larval migration are also assessed. Finally, an evolutionary IBM was also developed in order to explore the hydrodynamic selective constraints that may influence the spatio-temporal spawning patterns, in the framework of a natal homing hypothesis. For a comparative purpose, these methods are applied to both the Humboldt current system (HCS), which sustains the world largest anchovy stock, and to the Canary current system (CCS), where primary production is higher. The comparison suggests different seasons for optimal ichthyoplankton retention over the shelf and food abundance in the CCS. In contrast, optimal retention and food abundance occur at the same time in the HCS. This could explain why the HCS sustains the largest small pelagic fish stock.