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Ocean Science An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 08 Apr 2019

Submitted as: research article | 08 Apr 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Ocean Science (OS).

Fine-scale vertical structure of sound scattering layers over an east border upwelling system and its relationship to pelagic habitat characteristics

Ndague Diogoul1,6, Patrice Brehmer2,3,5, Yannick Perrot3, Maik Tiedemann4, Abou Thiam1, Salaheddine El Ayoubi5, Anne Mouget3, Chloé Migayrou3, Oumar Sadio2, and Abdoulaye Sarré6 Ndague Diogoul et al.
  • 1University Cheikh Anta Diop UCAD, Institute of Environmental Science (ISE), BP 5005 Dakar, Senegal
  • 2IRD, Univ Brest, CNRS, Ifremer, LEMAR, Campus UCAD-IRD de Hann, Dakar, Senegal
  • 3IRD, Univ Brest, CNRS, Ifremer, LEMAR, DR Ouest, Plouzané, France
  • 4Institute of Marine Research IMR, Pelagic Fish, P.O. Box 1870 Nordnes, 5817 Bergen, Norway
  • 5Institut National de Recherche Halieutique INRH, Agadir, Morocco
  • 6Institut Sénégalais de Recherches agricoles ISRA, Centre de Recherches Océanographiques de Dakar-Thiaroye (CRODT), BP 2221 Dakar, Senegal

Abstract. Sound scattering layers SSLs distribution and their relationship to pelagic habitat characteristics is a first step to understand their role in ecosystem dynamics and their interactions with other pelagic components such as small pelagic fish. In this study two areas of the Senegalese shelf have been characterized during upwelling season corresponding to a cold inshore area and a deeper and warmer stratified offshore area that was sharply separated by a strong thermal boundary. Marine pelagic organisms usually aggregates and occurs as SSLs on echosounder. Mean SSL thickness and SSL vertical depth increase with continental shelf depth; thickest and deepest SSLs were observed in the offshore part of the continental shelf. SSLs preferendum was reported for stratified water conditions rather than fresh upwelled water. The SSLs spatiotemporal variability was mostly explained by bottom depth which influence depth, thickness, and biomass of the SSLs. Diel period and water physico-chemical characteristics had also an effect on SSL depth and SSL thickness but not on SSL biomass. Despite chlorophyll-a has statistically no effect on SSLs structure, we report that the chlorophyll-a peak was always located above or in the middle of the SSLs, often matching with the peak of SSLs biomass. Such observations indicate trophic relationships, highlighting SSLs being mainly composed of phytoplanktivorous organisms. Acoustic mapping technique of mixed layer depth is not always efficient in east border upwelling system. Lastly, over the Senegalese continental shelf the level of dissolved oxygen was not found limitative (no hypoxia) for SSLs marine pelagic organisms during upwelling event.

Ndague Diogoul et al.
Model code and software

Matecho: An Open-Source Tool for Processing Fisheries Acoustics Data Y. Perrot, P. Brehmer, J. Habasque, G. Roudaut, N. Behagle, A. Sarré, and A. Lebourges-Dhaussy

Ndague Diogoul et al.
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