Abstract:The coastal regions of the Gulf of Guinea constitute one of the major marine ecosystems, producing essential living marine resources for the populations of Western Africa. In this region, the Ivorian continental shelf is under pressure from various anthropogenic sources, which have put the regional fish stocks, especially Sardinella aurita, the dominant pelagic species in Ivorian industrial fishery landings, under threat from overfishing. Here, we combine in situ observations of Sardinella aurita catch, temperature, and nutrient profiles, with remote-sensing ocean-color observations, and reanalysis data of wind and sea surface temperature, to investigate relationships between Sardinella aurita catch and oceanic primary producers (including biomass and phenology of phytoplankton), and between Sardinella aurita catch and environmental conditions (including upwelling index, and turbulent mixing). We show that variations in Sardinella aurita catch in the following year may be predicted, with a confidence of 78%, based on a bilinear model using only physical variables, and with a confidence of 40% when using only biological variables. However, the physics-based model alone is not sufficient to explain the mechanism driving the year-to-year variations in Sardinella aurita catch. Based on the analysis of the relationships between biological variables, we demonstrate that in the Ivorian continental shelf, during the study period 1998-2014, population dynamics of Sardinella aurita, and oceanic primary producers, may be controlled, mainly by top-down trophic interactions. Finally, based on the predictive models constructed here, we discuss how they can provide powerful tools to support evaluation and monitoring of fishing activity, which may help towards the development of a Fisheries Information and Management System.
Le suivi morpho-sédimentaire des côtes, effectué, à travers des mesures de levés topographiques au DGPS à haute résolution spatiale (5 cm de précision) a permis d'identifier 7 profils de plage et de quantifier les changements morphologiques sur cette plage entre octobre 2014 et février 2016. Les profils de plage ont été identifiés à partir du profil topographique de la première mission de terrain (29 décembre 2014). Il s'en est suivi une interpolation de lignes 3D sur les modèles surfaciques (TIN), calculés à partir du logiciel ARCGIS 10.2.2. Les évolutions sédimentaires enregistrées sur ces profils ont montré un équilibre sédimentaire dans le secteur du Phare (±16000 m 3), suivi de sédiments engraissés entre le Phare et l'Aéroport (compris entre +3350 et +48880 m 3), dont certaines quantités ont été érodées entre la localité de Derrière Wharf et l'Aéroport (-1050 m 3). Ces évolutions traduisent l'instabilité du trait de côte et confirment le sens du transit sédimentaire de la dérive littorale de l'ouest vers l'est de la côte. Les quantités érodées pourraient s'expliquer par le piégeage des sédiments dans la baie de Port-Bouët dû aux effets conjugués des protections du canal de Vridi et du Trousans-fond qui entaillent l'avant-côte.
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