Senegal’s coastal waters are made rich by an unusual coastal phenomenon, according to a study published in 2017. Research on the oceanic and atmospheric mechanisms involved provide the knowledge we need for sustainable management of this indispensable resource for Senegalese food security.
The phenomenon of upwelling affecting the southern coast of Senegal, recently re-examined, is shaking up common theories on the subject. This coastal current, a product of oceanic and atmospheric forces, is even highly unusual. “Its very specific characteristics make it a precious ally for Senegalese artisanal fishers exploiting the coastal waters,” explains marine ecologist Patrice Brehmer of IRD. With specialists in physical oceanography, he has recently devoted a study to the subject, combining computer modelling and oceanographic campaigns.
The phenomenon of upwelling affects many coasts on all continents. It is primarily connected to the coastal winds that help to push surface water out to sea. In a volume conservation effect, this is logically replaced by water coming up from the depths, which is colder and richer in nutrients. “This powerful oceanic conveyor belt helps to enrich coastal environments, but also offshore environments, because the water that comes up from the depths is in turn pushed out to sea,” indicates oceanographer and physicist Siny Ndoye, the lead author of the study. Upwelling therefore supplies the trophic chain of particularly rich zones, such as that situated off Peru, which is the most fish-filled in the world.
“Our work modelling the South Senegalese upwelling has shown that the water rises are of quite low intensity and very localised in a limited zone,” confirms his colleague Xavier Capet. These characteristics are due to the topography of the area, with a coastline interrupted by the imposing Cap-Vert peninsula, and the specific climate conditions of West Africa. Paradoxically, the limited power of this upwelling is highly beneficial for species living near the coast. “Although the enrichment of the environment is only moderate, the coastal retention is high,” explains Xavier Capet. “The low intensity of the phenomenon comes with quite limited transport out to sea.”
In concrete terms, little cold water and nutrients are pushed out to sea, and they are instead distributed along the coast from the point where they rise. The primary production generated by this nutrient input thus benefits the whole marine coastal fauna. “The Petite-Côte, located between the south of Dakar and the Gambia estuary, is an important fishing zone, for both the livelihoods of Senegalese artisans and the food security of the country. The new knowledge provided by this study of the local South Senegalese upwelling will allow better management of the environment and its resources,” explains Patrice Brehmer. Research on the oceans, on their interactions with the atmosphere and on marine fauna is an essential priority for achieving the sustainable development goals.