David Viviane auteur aut IRD Habasque Jérémie auteur aut IRD Roudaut Gildas auteur aut IRD Marie L. auteur aut IRD Thibault D. auteur aut IRD Lebourges Dhaussy Anne auteur aut IRD Capet X. auteur aut IRD Machu Eric auteur aut IRD text journalArticle eng text/pdf reformatted digital access The coastal area of north-west (NW) Africa is a highly productive ecosystem due to the presence of a strong upwelling. This ecosystem supports large populations of small pelagic fish, such as sardinellas, which have significant socio-economic value for local populations. In this study, we analyzed the acoustic data collected during a one-month survey along the Senegalese coast at the beginning of the upwelling season. Hierarchical clusterings were performed to classify the acoustic data from the epipelagic zone (down to 120 m-depth) separately for daytime and nighttime. The analysis identified five echo-groups during the day and six at night. The resulting echo-groups were then compared to stratified midwater trawl samplings to support hypotheses about the organisms responsible for the echoes. Additionally, a remotely operated towed vehicle (called Scan-fish) was used to monitor environmental variables down to 100 m depth. Two machine learning models were applied to link the classified echo-groups to the environmental data for both day and night. Each daytime echo group had a corresponding nighttime echo group, with also similar environmental preferences. Fish schools were mainly found in shallow coastal waters while dense sound-scattering layers detected at 38 kHz, likely composed of small fish or fish larvae, were observed in the temperature range of 17 degrees-21 degrees C for both day and night. The other echo-groups were composed of fluid-like zooplankton or gas-bearing zooplankton. The sixth night echo-group corresponded to migrant organisms and was predominant at night. Overall, the analyses of the abiotic habitats for each echo-group allow us to better understand the organism distributions during the beginning of the NW Africa upwelling season. specialized Active acoustics Micronekton Senegal Upwelling SENEGAL ATLANTIQUE 036 082 251 104113 [14 ] 2025 0924-7963 https://www.documentation.ird.fr/hor/fdi:010094808 10.1016/j.jmarsys.2025.104113 0924-7963 [F B010094808] https://www.documentation.ird.fr/hor/fdi:010094808 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2025-09/010094808.pdf IRD - Base Horizon / Pleins textes 2025-09-24 2025-11-04 fdi:010094808 fre