MEPS 592:225-242 (2018)  -  DOI: https://doi.org/10.3354/meps12502

ABSTRACT: Effective management of potential fisheries in deep-sea environments (>200 m depth) requires better understanding of species distributions and related environmental factors. We described the bathydemersal fish assemblages (300-2100 m) off the western coast of Baja California, Mexico (23-32°N) and their relationship with latitude, depth, temperature, dissolved oxygen (DO), salinity, organic matter, sediment composition and organic carbon. We collected a total of 3417 fish using a benthic sledge (18 orders, 36 families and 77 species: 27 mesopelagic, 10 bathypelagic and 40 bathydemersal; 8 new records). We found 5 latitude-depth assemblages: South-Shallow (<28°N, <700 m), South-Medium (<28°N, 700-1300 m), South-Deep (<28°N, 1430 m), North-Medium (>28°N, 700-1300 m) and North-Deep (>28°N, 1300-2100 m). Tropical species dominated southern assemblages, whereas northern assemblages shared species with the Southern California assemblages. A reduced number of bathydemersal species (15 species) dominated the upper slope. The middle slope (27 species) was the most diverse stratum, and lower abundances generally characterized the lower slope (12 species). Depth, DO and different water masses affected the distribution of bathydemersal species. These results are consistent with slope assemblages from different ocean basins, supporting the hypothesis that slope fish assemblages generally occupy discrete vertical ranges determined by depth and the environmental factors associated with it.

KEY WORDS: Bathydemersal fish · Environmental factors · Oxygen minimum zone · Southern Californian Pacific ecoregion · Salinity · Slope zonation · Latitudinal transition · Tropical species