Conducted jointly by UGB and IRD, this research explores the dynamics of sardinella larvae in the Gulf of Guinea.
The Essentials: Conducted jointly by UGB and IRD, this research explores the dynamics of sardinella larvae in the Gulf of Guinea.
Yago Ya Hilaire Amemou, researcher at UMMISCO (Université Gaston Berger de Saint-Louis Sénégal).
Thesis defended in 2021 at the doctoral school École doctorale Sciences de l'environnement d'Île-de-France (Paris ; 1992-....).
This research is the product of an international joint supervision between several partner institutions.
Listed in the ABES/STAR network, this thesis meets the rigor criteria of French higher education.
Context and Research Problem
Sardinella aurita, the predominant species in the Gulf of Guinea, forms the backbone of artisanal fishing in the region, essential to the food security of millions of people. The recruitment of sardinella larvae depends on environmental conditions, notably ocean circulation dynamics and food availability. Upwelling, a phenomenon characterized by the rise of deep, nutrient-rich waters, plays a central role in marine productivity. However, the mechanisms governing the interaction between the dispersal, growth, and mortality of sardinella larvae remain only partially understood, particularly in the northern part of the Gulf of Guinea.
The study of biophysical systems helps improve understanding of these complex interactions. Numerical models provide a framework for integrating hydrodynamic, biogeochemical, and biological processes, facilitating the assessment of conditions favorable to larval recruitment. Evaluating these parameters is crucial for developing sustainable artisanal fishing management strategies that account for the vulnerability of marine ecosystems to climate change and human activities.
Methodology
This research relies on an integrated numerical modelling approach, combining hydrodynamic, biogeochemical, and biological data. The models were calibrated to simulate the dispersal and growth processes of sardinella larvae in the Gulf of Guinea. Emphasis was placed on identifying retention zones, where conditions are optimal for larval survival and growth.
Simulations were carried out taking into account various environmental factors, notably temperature, salinity, and nutrient concentration. Results were validated against field data, making it possible to assess the accuracy of the models in predicting the population dynamics of sardinella larvae.
Key Findings
The results indicate that coastal areas of the Gulf of Guinea, characterized by the presence of eddies, favor the retention of sardinella larvae. These eddies act as natural barriers, increasing larval survival chances by keeping them in nutrient-rich zones. Sardinella spawning periods coincide with upwelling seasons, notably in February and August, when nutrients are available at the surface.
Optimal depths for larval retention lie between 0 and 50 meters. These depths correspond to simulated prey distribution maxima, indicating that food availability is a determining factor for larval growth. The weakening of the Guinea Current's intensity at depth also appears to influence larval retention dynamics.
Discussion and Outlook
The study of interactions between ocean circulation, food availability, and sardinella larvae recruitment underscores the importance of an integrated approach to marine resource management. The results obtained highlight the need to adapt management policies to account for the specific environmental conditions that influence larval survival.
The economic implications of this research are significant. Effective marine resource management, based on scientific data, could strengthen food security while supporting local economies. Collaboration between academic institutions and stakeholders in the fishing sector proves crucial to ensuring a sustainable future for coastal communities.
The results also open up prospects for future research. Exploring interannual variability in environmental conditions and its impact on larval recruitment could enrich our understanding of ecological dynamics in the Gulf of Guinea. In addition, integrating new modelling and environmental monitoring tools could help refine management and adaptation strategies in the face of climate change, thereby ensuring the sustainability of artisanal fisheries and food security in the region.
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Sources and Access
Yago Ya Hilaire Amemou. Modélisation biophysique de la dispersion et de la croissance des larves de sardinelles dans le Golfe de Guinée. Ecosystèmes. Sorbonne Université; Université Félix Houphouët-Boigny (Abidjan, Côte d'Ivoire), 2021. Français. ⟨NNT : 2021SORUS185⟩. ⟨tel-03681804⟩