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Mbaye B.C.,Laboratoire Of Physique Of Latmosphere Et Of Locean Simeon Fongang Lpao Sf | Mbaye B.C.,University Pierre and Marie Curie | Brochier T.,Institute Of Recherche Pour Le Developpement Ird | Echevin V.,University Pierre and Marie Curie | And 5 more authors.
Fisheries Oceanography | Year: 2015

Sardinella aurita is the most abundant small pelagic fish in the Senegalese-Mauritanian region. The success of its reproduction crucially depends on the local circulation as this determines whether larvae reach coastal nursery areas favorable to their survival or are dispersed into the open ocean. As a first step towards evaluating sardinella vulnerability to climate-driven hydrodynamical changes, this study aims at underpinning how transport pathways drive optimal spatial and seasonal patterns for sardinella reproduction. We have used two estimates of the Senegalese-Mauritanian coastal seasonal circulation simulated by two hydrodynamical model configurations that differ in their forcing and topography. Nursery areas are determined by evaluating coastal retention with a Lagrangian individual-based model that accounts for processes such as diel vertical migration and mortality as a result of lethal temperature exposure. Our results suggest that the shelf zones located at the Arguin Bank (19.5°N-21°N) and south of Senegal (12°N-14.75°N) are highly retentive. We find maximum retention rates in July-August and November-December over the Arguin Bank; from February-July and November-December over the southern Senegalese shelf; and lower retention rates over the central region (14.75°N-19.5°N) that are locally maximum in June-July when the upwelling weakens. These retention areas and their seasonality are in agreement with previously reported spawning patterns, suggesting that the Sardinella aurita spawning strategy may result from a trade-off between retention patterns associated with the seasonal circulation and food availability. Exposure to lethal temperatures, although not well studied, could be a further limiting factor for spawning. The Lagrangian analysis reveals important connectivity between sub-regions within and south of the system and hence underlines the importance for joint management of the Sardinella aurita stock. © 2015 John Wiley & Sons Ltd.

Diakhate M.,Laboratoire Of Physique Of Latmosphere Et Of Locean Simeon Fongang Lpao Sf | Diakhate M.,Laboratoire dOceanographie et Climat | de Coetlogon G.,Laboratoire Atmosphere | Lazar A.,Laboratoire dOceanographie et Climat | And 2 more authors.
Quarterly Journal of the Royal Meteorological Society | Year: 2016

Tropical Atlantic sea-surface temperatures (SSTs) maximum intraseasonal variability (ISV) and their interaction with local surface winds are investigated, applying statistical analysis to observations and to a recent coupled reanalysis over the 2000-2009 decade. Five cores of strong ISV emerge, with standard deviation reaching about 1 °C in frontal areas of the three main upwelling systems: equatorial, Angola-Benguela and Senegal-Mauritania (the southern side of the Canary upwelling). West of 10 °W along the Equator, a 20-60-day peak caused by tropical instability waves is shown to generate surface wind anomalies through the adjustment of the horizontal surface pressure gradient in addition to the modification of near-surface atmospheric stratification. East of 10°W along the Equator, an intense biweekly oscillation increases the ocean and atmosphere ISV. In the two coastal upwelling fronts, intraseasonal SST anomalies resemble each other. They are shown to be influenced by coastal Kelvin waves in addition to large-scale wind forcing. Over the Angola-Benguela upwelling, coastal wind bursts controlling the SST ISV are associated with anomalously strong pressure patterns related to the Madden-Julian Oscillation, the St Helena anticyclone and the Antarctic Oscillation. In the Senegal-Mauritania upwelling, the wind anomalies mainly linked to the Azores anticyclone in the southern front during November to May appear to be connected to the Saharan heat-low in the northern front from June to September. In all five regions and as expected for such upwelling regimes, vertical oceanic mixing represents the dominant term in the mixed-layer heat budget. In the equatorial band, as found in previous studies, horizontal advection is equally important, while it appears surprisingly weak in coastal fronts. Finally, a striking result is the general lack of surface wind signal related to the SST ISV in the coastal upwellings. © 2016 Royal Meteorological Society.

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