Structure and zonation of demersal and deep-water fish assemblages off the Cabo Verde archipelago (northeast-Atlantic) as sampled by baited longlines

The assemblages of the demersal and deep-water fish assemblages of the Cabo Verde archipelago are described for the first time from a total of 20 longline hauls that extends from coastline to 1200 m water depth. A total of 98 species from 47 different families were caught, and despite the changes of biogeographic affinities with depth, the majority of the species are from a Subtropical and Tropical origin or have a broad geographic distribution (Wide and Amphiatlantic distributions) with small affinities with the Macaronesian islands and the Mediterranean. Depth distribution profiles show a clear turnover of species with depth, and an increase in the depth distribution range of the deeper living species. Furthermore, the indices of species abundance, biomass and the number of species caught, significantly decreased with increasing depth. Four main fish assemblages in a depth-aligned structure are proposed in the present work. A shelf assemblage mainly distributed above the 150 m depth strata, a shelf-break/upper-slope assemblage mainly between the 150-350 m depth strata, a deep/upper-slope assemblage between the 300-600 m depth strata, and a mid- deep/mid-slope assemblage mainly distributed below the 600 m. Species abundances and diversity found below 200 m is relatively low compared with shallow waters. The observed depth zonation of the slope assemblages, roughly agrees with the expected occurrence or influence of different water masses: shelf and surface mixing and seasonal thermocline depth zone, the depth range of occurrence of the intermediate waters (North Atlantic Central Water-NACW), the South Atlantic Central Water-SACW), and Atlantic Equatorial Water-AEW), a mixing or overlapping zone of previous intermediate water masses with the Antarctic Intermediate Water (AAIW), and the Mediterranean Outflow Water (MOW), and a deeper zone where the AAIW predominate.