| Summary: | Data from EU-Spain (Instituto Español de Oceanografía) bottom trawl surveys in the NAFO Regulatory Area (2002- 2011) were analyzed to examine evolution patterns in the Southern of Grand Banks (NAFO Div. 3NO) groundfish assemblage structure in relation to depth. The 1160 hauls from the slope surveys spanned between 38 and 1460 m in depth. We focused on the 28 most abundant species, which made up 92.6 % of the catch in terms of biomass. The fish biodiversity results (221 fish species) are higher than in other ecosystems, and the highest value is reached in the deeper assemblage, with diversity H=2.23. Assemblage structure was strongly correlated with depth. For the most part, changes in assemblages seem to be fairly continuous although there were more-abrupt changes at 300 m. Three main groups and five assemblages were identified. Cluster I (Shallow) comprised the strata with depths lesser than 300 m; cluster II (Intermediate) contained the depth strata between 301 and 1000 m and cluster III (Deep) the depth strata greater than 1001 m. Cluster I could be further subdivided into two sub-clusters. Cluster Ia comprised the strata with depth less than 150 m and cluster Ib the strata with depths between 151 and 300 m. Two sub-cluster were identified in cluster II: IIa contained depths between 301 m and 600 m and IIb depths between 601 and 1000 m. Despite dramatic changes in biomass and abundance of the species in the area, the boundaries and composition assemblages seem to be similar to the previous period. Although some changes were evident, the main ones were replacement of the dominant species in several assemblages and bathymetric range extension of distribution of some species. Yellowtail flounder (Limanda ferruginea) appears to be as the dominant species in shallow assemblages instead of Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) that were dominant in the period before the collapse in the area; in the intermediate assemblages redfish (Sebastes spp) is the dominant species. The ...
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