The community structure of demersal fish species from bottom-trawls off Namibia and the West coast of South Africa.

Abstract

Changes in the structure and composition of the demersal fish assemblages are assessed using a variety of ecosystem indicators known to capture such changes, which may be induced by bottom-trawling. The aim of this study was to investigate whether there are any structural changes in demersal fish assemblages by way of latitudinal variation. The study was conducted from the Kunene River to Agulhas Bank during the 2007 demersal surveys. Abundance and biomass data was analysed using cluster analysis, non-metric multidimensional scaling, abundance biomass comparison curves, and similarity profiles in PRIMER v6 software. The dendrogram identified three main groups, two in northern Benguela, separated into shelf and slope assemblages and one in the southern Benguela, without any distinction between shelf and slope at 19% similarity. Identified assemblages are spatially distinct. The average similarities on the continental shelf in northern Benguela were driven by the following top three species: M. capensis, Sufflogobius bibarbatus and Trachurus trachurus capensis; on the continental slope they were driven by M. paradoxus, Nezumia micronychodon and Helicolenus dactylopterus; while the similarities in southern Benguela assemblages were driven by M. paradoxus, H. dactylopterus and Lophius vomerinus, in order of % contribution.