Species richness, taxonomic diversity, and taxonomic distinctness of the deep-water demersal fish community on the Northeast Atlantic continental slope (ICES Subdivision VIa)

The fish community on the Atlantic deep continental shelf and upper slope to the northwest of Scotland has been the subject of biological studies for more than a century, and subject to bottom-trawl fishing for around 25 years. In this work, we examine trends in biodiversity of the deep-water demersal fish community revealed by a decade of trawl surveys by Marine Scotland-Science. The composition and structure of the fish assemblage was described using species richness as well as the descriptors of community interrelatedness: taxonomic diversity (Delta) and taxonomic distinctness (Delta*). Results revealed no temporal trends in community composition. The most significant factor in determining richness and taxonomic diversity of the demersal fish fauna was depth, and to a lesser extent latitude. Diversity and distinctness decreased with increasing depth and showed a complex relationship with latitude, while richness peaked at depths around 1400 m. This study shows taxonomic measures of diversity and distinctness to be sensitive indicators of ecological conditions in the deep-water fish community, with respect to depth and latitude, and the fact that no temporal trends were detected suggests that the structure of the fish community at exploitable depths on the Scottish slope has remained stable over the period 1998-2008. These findings imply that care should be taken when planning spatial measures designed to safeguard deep-water fish biodiversity because the optimal area recommended for protection is strongly dependent on the choice of metric used.