Persistence and Variation on the Groundfish Assemblages on the Southern Grand Banks (NAFO Divisions 3NO): 2002-2011

Abstract

Data from EU-Spain (Instituto Espanol de Oceanografia) bottom trawl surveys in the NAFO Regulatory Area (2002–2011) were analyzed to examine patterns on the South of Grand Banks (NAFO Div. 3NO) of groundfish assemblage structure and diversity 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. 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. Five assemblages were identified. Two shallow assemblages were found in the shelf. Assemblage I (Shallow) comprises the strata with depths lesser than 150 and include yellowtail flounder (Limanda ferruginea), American plaice (Hippoglossoides platessoides), Northern sand lance (Ammodytes dubius), moustache sculpin (Triglops murrayi), capelin (Mallotus villosus) and web sculpin (Hemitripterus americanus). Assemblage II (Shallow) includes the strata with depths between 151 and 300 m and comprises Atlantic cod (Gadus morhua), American angler (Lophius americanus), wolfish (Anarichas lupus) and thorny skate (Amblyraja radiata). Assemblage III (Intermediate) contains the depth strata between 301 and 600 m. Redfish (Sebastes spp.), spotted wolfish (Anarichas minor), Arctic eelpout (Lycodes reticulatus), Northern wolfish (Anarichas denticulatus), white hake (Urophycis tenuis), witch flounder (Glyptocephalus cynoglossus) and longfin hake (Phycis chesteri) were included in the intermediate assemblage. Finally, we found two deep clusters: Assemblage IV (Deep) contains the depths between 601 and 1000 m, and Assemblage V (Deep) the depth strata greater than 1001 m. Greenland halibut (Reinhardtius hippoglossoides), marlin-spike (Nezumia bairdii), roughhead grenadier (Macrourus berglax) and spinytail skate (Bathyraja spinicauda) formed Assemblage IV. Snubnosed spiny eel (Notacanthus chemnitzii), blue antimora (Antimora rostrata), Northern cutthroat eel (Syphanobranchus kaupii), roundnose grenadier (Coryphaenoides rupestris), black dogfish (Centroscyllium fabricii), Arctic skate (Amblyraja hyperborea) and longnose chimera (Harriotta raleighana) made up the deepest assemblage. Despite dramatic changes in biomass and abundance of the species in the area, the boundaries and composition of the assemblages seem to be similar to the period before the collapse. Although some changes were evident, the main ones were replacements of the dominant species in several assemblages and bathymetric range extension of distribution of some species. Yellowtail flounder appears to be the dominant species in the shallowest assemblage instead of Atlantic cod and American plaice that were dominant in the period before the collapse in the area; redfish is the dominant species in the second shallow and intermediate assemblages. Diversity appears inversely related to biomass in the different assemblages. Despite the fishing effort in the deep waters of the Grand Banks, the overall pattern of demersal fish assemblages remains similar over time. This pattern is similar in other Atlantic areas; it indicates that changes in the fish populations in Northwest Atlantic have been produced on a large scale and are not limited to specific areas.