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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14524

Mesopelagic fish assemblages in the Mauritanian Upwelling System off Northwest Africa with oxygen as a major driving force

Sabrina E. Duncan*, Wilhelm Hagen, Heino Ove Fock

*Corresponding author:

ABSTRACT: The aims of this study were to determine the community composition and environmental drivers of mesopelagic fishes in the Mauritanian upwelling system. Mesopelagic fish communities were sampled at seventeen stations in August of 2016, off the coast of Senegal and Mauritania using a non-closing rectangular midwater trawl (RMT). This subregion is the most productive area of the Canary Current and it has a pronounced and permanent oxygen minimum zone (OMZ). The sampling area was mainly composed of low-oxygenated South Atlantic Central Water, except for one station, where North Atlantic Central Water prevailed. Three distinct mesopelagic fish communities were identified. One community occurred in the vicinity of a cold-water eddy and was dominated by the myctophid Benthosema glaciale. In contrast, the gonostomatid Cyclothone spp. prevailed in the other two communities and made up 62% and 51% of the total fish abundance. Our analyses revealed that the environmental factors that primarily influenced the composition of these mesopelagic fish assemblages were the oxygen concentrations at 10 m, 100 m, and 600 m. The present study showed that the mixing of water masses at frontal zones leads to communities representative of both water masses. In the case of the Mauritanian upwelling region, a high portion of the mesopelagic fish species were well adapted to OMZ conditions.