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Many descriptions of paralarval and juvenile cephalopods are poor. By using DNA barcoding, a global bioidentification system for animals, along with morphological investigation, we can confirm species identifications. We have a better chance of eliminating misidentifications and, therefore, documenting the correct abundance and distribution of cephalopods within an area by combining morphological and molecular evidence. The central objectives of this study are to: (1) compare morphological vs molecular identification of cephalopods and (2) determine the occurrence of cephalopods within the deep scattering layer (DSL) within warm core eddies. The specimens reported here were collected between 2014 and 2016 during three transatlantic cruises from Galway, Ireland to St John's, Newfoundland, with a focus on assemblages in warm-core mesoscale eddies on the western part of the transect. Samples were collected from the DSL at multiple stations across mesoscale eddies. In total, 301 cephalopods belonging to 29 species were collected. Not only does our study increase the knowledge of abundance and diversity of pelagic cephalopods in this area, but it also provides sequences for species for which no comparative sequences were previously available. By examining the match/mismatch between morphological and molecular identifications, we highlight a need for revisions in some taxonomic groupings such as the family Cranchiidae.

Variability in mesopelagic fish assemblages of the deep-scattering layer were explored in relation to mesoscale anticyclonic (warm-core) eddies in the western North Atlantic Ocean. Exploratory fishing with a mid-water herring trawl was combined with oceanographic sampling aboard the RV Celtic Explorer in the Spring of 2015 and 2016 to characterize mesopelagic fish assemblages along transects through anticyclonic eddies identified using real time satellite-derived sea level anomaly. Sampling yielded a total of 6087 fish specimens, representing at least 109 species across 38 families. The families Myctophidae and Stomiidae were the most speciose taxa sampled and comprised >50% of total catch abundance in each year. Species richness and diversity (H’) were significantly higher in sets occurring inside relative to outside the eddy structures. Community analyses indicate significant differences in daytime assemblage structure between both depth groups (shallow 200–400 m versus deep 400–700 m) and eddy groups (inside versus outside), with ordination discrimination of 5 pelagic fish assemblages related to eddy groups. Anticyclonic eddies also harbored more juveniles and rare species, including species with more southerly distributions within the Gulf Stream. Our results indicate anticyclonic eddies may play an important role in structuring fish assemblages and the dispersion of mesopelagic species in the Northwest Atlantic.

The distribution and density of Deep Scattering Layers (DSLs) were quantified along North Atlantic transits from Ireland to the Grand Banks of Newfoundland in the springs of 2012, 2013 and 2014 employing a calibrated Simrad EK60 echo sounder at 38 kHz. Concurrently, Sippican T5 XBTs (eXpendable Bathy Thermographs) were used to profile temperatures to 1800 m. In each year the scattering layers spanned the deep basin at depths ranging from near surface to approximately 900 m, but annual mean densities differed significantly. Higher DSL densities were recorded during years that exhibited higher sea temperatures at the depths of major DSL concentration (400–600 m), higher sea level anomalies and stronger eastward geostrophic currents. The highest concentration of the DSLs in each year was found in the area east of the Grand Banks that corresponded with areas of anticyclonic eddies. In this region DSL densities in 2014 were among the highest recorded worldwide (>7000 m 2 nautical mile – 2 ). Midwater fishing indicated DSLs were dominated by Myctophids and Sternoptychids. Anticyclonic eddy formation is discussed as a possible means of transport and aggregation of the DSLs in that region, where oceanographic influences may play a dominant role in the distribution and density of the DSLs and upper trophic level fishes.