Diogoul N. auteur aut IRD Brehmer Patrice auteur aut IRD Perrot Yannick auteur aut IRD Tiedeman M. auteur aut IRD Thiam A. auteur aut IRD El Ayoubi S. auteur aut IRD Mouget A. auteur aut IRD Sarré A. auteur aut IRD text journalArticle eng text/pdf reformatted digital access Understanding the relationship between sound scattering layers (SSLs) and pelagic habitat char-acteristics is a substantial step to apprehend ecosystem dynamics. SSLs are detected on echo sounders representing aggregated marine pelagic organisms. In this study, SSL characteristics of zooplankton and micronekton were identified during an upwelling event in two contrasting areas of the Senegalese continental shelf. Here a cold upwelling-influenced inshore area was sharply separated by a strong thermal boundary from a deeper, warmer, stratified offshore area. Mean SSL thickness and SSL vertical depth increased with the shelf depth. The thickest and deepest SSLs were observed in the offshore part of the shelf. Hence, zooplankton and micronek-ton seem to occur more frequently in stratified water conditions rather than in fresh upwelled water. Diel vertical and horizontal migrations of SSLs were observed in the study area. Diel pe-riod and physicochemical water characteristics influenced SSL depth and SSL thickness. Alt-hough chlorophyll-a concentration insignificantly affected SSL characteristics, the peak of chlo-rophyll a was always located above or in the middle of the SSLs, regularly matching with the peak of SSL biomass. Such observations indicate trophic relationships, suggesting SSLs to be mainly composed of phytoplanktivorous zooplankton and micronekton. Despite local hypoxia, below 30m depth, distribution patterns of SSLs indicate no vertical migration boundary. The results increase the understanding of the spatial organization of mid-trophic species and migra-tion patterns of zooplankton and micronekton, and they will also improve dispersal models for organisms in upwelling regions. specialized SENEGAL ATLANTIQUE 032 040 Jech M. ed. edt IRD 4 54 50-51 2022 2618-1371 ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST), Somone (SEN), 2022/04/25-28 https://www.documentation.ird.fr/hor/fdi:010089773 2618-1371 [F B010089464] https://www.documentation.ird.fr/hor/fdi:010089773 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2024-03/010089773.pdf IRD - Base Horizon / Pleins textes 2024-02-15 2024-03-01 fdi:010089773 fre