The deep scattering layer micronektonic fish faunas of the Atlantic mesopelagic ecoregions

Three hundred and twenty-nine species of micronektonic fishes were identified in 1040 midwater trawl collections taken between 1963 and 1974 from the North and South Atlantic, the Mediterranean, the Caribbean and the Gulf of Mexico. The target of most tows was the deep scattering layer, and consequently the dominant species in the material were those that were concentrated in the layer. The results only generally confirm the 11 Atlantic mesopelagic ecoregions previously recognized. The geometric mean of the proportion of joint occurrences (GMPJO) of species with tows within each ecoregion was used to characterize the faunas of the ecoregions. The ecoregion affinities of fishes were compared to those of decapod shrimp in the same collections. The fish and shrimp faunas of ecoregions could be distinguished by GMPJO values, but the ranges of species favoring each ecoregion varied widely in extent and did not conform well to ecoregion boundaries or features of circulation. This suggests that co-occurring species respond differently to the physical properties and resulting biological factors defining mesopelagic ecoregions.