Influence of anticyclonic, warm-core eddies on mesopelagic fish assemblages in the Northwest Atlantic Ocean

Abstract

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.