Biodiversity and distribution of deep-pelagic fishes from the subtropical Southwestern Atlantic

We conducted a biodiversity assessment of deep-pelagic fish species in the Subtropical Southwestern Atlantic Ocean, using three complementary fishing methods across depths from 97 to 2570 m between 1996 and 2022. This analysis includes 926,657 specimens, representing 74 species from 11 orders and 18 families. Using these data, we present relationships with environmental factors and a detailed species inventory illustrating diversity and dominance patterns. Distinct from other Southwestern Atlantic ecoregions, our findings reveal high species dominance coupled with relatively low diversity. Among the collected taxa, Diaphus dumerilii (Myctophidae) and Maurolicus stehmanni (Sternoptychidae) constituted over 90 % of all specimens. Analysis of their distribution in relation to water properties reveals that these species exhibit a greater tolerance to a broad range of temperature and salinity conditions, an adaptive trait that likely drives their ecological dominance in the deep-pelagic ecosystems of the study area. The dominance pattern held consistently across all fishing methods, though we observed notable variation in species diversity and abundance between collection techniques. This study provides an important assessment of the deep-pelagic fish fauna in this region, establishing a valuable baseline for future research targeting this largely unexplored fauna.