Structure and zonation of demersal fish assemblages off the Azores Archipelago (mid-Atlantic)

The assemblages of the demersal fish fauna of the Azores Archipelago are described from longline surveys that extended from the coastline to 1200 m water depth. A total of 104 fish species from 47 different families were caught, and despite the changes of biogeographic affinities with depth, most species caught are of subtropical origin (mainly from the Eastern Atlantic/Mediterranean areas) or have a broad geographic distribution. Four large-scale fish assemblages following a depth-aligned structure were found: a shallow-shelf/shelf-break assemblage at depths < 200 m, an upper-slope assemblage at 200-600 m, a mid-slope assemblage at 600-800 m and a deep mid-slope assemblage at 800-1200 m. Within the main shallow assemblage, 4 small-scale fish assemblages were found: an inner-shelf-island assemblage, an outer-shelf-island assemblage, a seamount/island-shelf/shelf-break assemblage and a transitional shelf/break assemblage. The bathymetric delineation of the mid-slope assemblages coincides with the known distributions of the North Atlantic Central Water (NACW), Mediterranean Water (MW) and the upper influence of the intermediate waters in the region: the northern sub-polar waters (Subarctic Intermediate Water [SAIW], the Labrador Sea Water [LSW]) and the Antarctic Intermediate Water (AAIW). The delineation of the shallow small-scale fish assemblages appears to be determined by small-scale environmental factors (e.g. bottom characteristics, seamounts or island areas).