Mesopelagic fish distribution in the southwest Atlantic in relation to water masses

A total of 150 mesopelagic fishes, representing 23 families and 47 species, were collected at 18 fishing stations occupied during four research cruises between 1988 and 1995. The main objectives of these cruises were to collect biological data of short-fin squid, Illex argentinus, and southern blue whiting, Micromesistius australis, in the southwest Atlantic within coordinates 36°–56°S and 44°–62°W. Different types of gear at a maximum depth of 1000 m were used. Myctophidae was the most diverse family, followed by Stomiidae, Sternoptychidae, Notosudidae and Melamphaidae. The myctophid Gymnoscopelus (G.) nicholsi and the gempylid Paradiplospinus gracilis were the most abundant species. Zoogeographic grouping of the 47 species on the basis of centres of distribution in relation to the hydrological conditions and types of water masses indicated that the sub-Antarctic species were the most numerous (18), followed by tropical–sub-tropical (13), sub-Antarctic–sub-tropical convergence (8 spp.) and widespread species (8). The transport of the fish fauna by means of an anticyclonic frontal eddy of the Brazil Current out of the sub-tropical zone into the sub-Antarctic is discussed.