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

Abstract

Data from EU-Spain (Instituto Español de Oceanografía) 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 wate...

Demersal groundfish assemblages and depth-related trends on Flemish Cap (NAFO division 3M): 2004–2013

“…All analyses agree that species follow two main patterns: shallow or deep, even if we can observe one more (intermediate assemblage with some species superimpose). While we found three assemblages, the strongest boundary was at 600 m where the PS value was lowest, a result consistent with previous analyses (Paz and Casas, 1996;González-Troncoso et al, 2006;Nogueira et al, 2013). However, our PS value at this bound-ary was lower than that found by Paz and Casas (1996), suggesting stronger zonation in the 2004-2013 period than in the 1989-1994 period.…”

“…In line with this assertion, diversity was lowest on the shelf and upper slope, which are the regions where the traditional commercial species, such as Atlantic cod and redfish, are found. Similar results were found in Flemish Cap by Paz and Casas (1996) and González-Troncoso et al (2006), and in the South of the Grand Banks by Nogueira et al (2013). Diversity in the shallow assemblage is lower and more similar to those found by Paz and Casas (1996) before the collapse for the period 1989-1995, than those found by González-Troncoso et al (2006) for the period 1996-2002 during the collapse.…”

“…This method is unaffected by double-zeros, i.e., tows in which both species that are being compared are absent (Kendrick and Francis, 2002). We used PCA to facilitate the comparison with previous works in near and same areas (Mahon et al, 1998;González-Troncoso et al, 2006;Lorenzo et al, 2011;Nogueira et al, 2013) and to verify the results of the CA with the results of another ordination method. Species loadings on the principal components (PCs) were used to identify groups of species that tend to co-occur (i.e., assemblages).…”

“…Mahon and Smith (1989) identified similar assemblage structure on Scotian Shelf and in the Bay of Fundy from 1970 to 1981. Gomes et al (1992) found six assemblages over 16 years on the Grand Banks of Newfoundland; Nogueira et al (2013) found five assemblages in the South of the Grand Banks (Regulatory Area of NAFO [NRA] Divisions 3NO). Previous works on the Flemish Cap (NRA Div.…”