Comparative analysis of pelagic compartment organization by bathymetric strata in the Canary Current Large Marine Ecosystem [résumé]
Résumé
The Canary Current Large Marine Ecosystem (CCLME) is located along the North West African coast from Morocco to Guinea Bissau. In this work, 14 Nansen fisheries acoustics surveys have been led from the southern border of Senegal (12.15°N) to the Cape Blanc (20.77°N) during the hot wet season, i.e., outside the seasonal upwelling period, from 1995 to 2015. The aim of this study was to scrutinize the water column organization in a bathymetric gradient starting from the coast to the offshore area, discretised in three areas: inshore (< 150m), transition (150-500m) and off shore (> 500m). Here, we worked on acoustic sound scattering layers (SSL) and on the whole water column through echointegrated data (EI). SSL and EI descriptors highlighted sig-nificant difference between the three depth strata. Study of the Diel Vertical Migration (DVM) highlighted that volume backscattering coefficient (proxy of pelagic abundance) vertical profile from transition area has a pattern globally similar to offshore one while inshore presented an inversed pattern. Analyse of annual change using EI descriptors reveal one common trait: the number of SSLs significantly increase whatever the depth strata considered. This study high-lights differences and similarity in water column organization between depth strata.