Three-dimensional distribution of larval fish habitats at the entrance of the Gulf of California in the tropical-subtropical convergence region off Mexico (April 2012)

Larval fish habitats and their representative species were analyzed in relation to water mass distribution and mesoscale processes at the entrance of the Gulf of California during April 2012. Results show that the oxygenated Gulf of California Water (GCW) spread south near Cabo Corrientes, above the hypoxic (>44 μmol kg-1) Subtropical Subsurface Water (StSsW), causing strong stratification. Two mesoscale eddies south of Cabo San Lucas entrapped surface oxygenated Transitional Water and sunk hypoxic waters to ∼100 m depth. These conditions defined two larval fish habitats that extended horizontally over most of the study area and were vertically separated by the eddy-modulated oxycline depth: a surface habitat associated with the southwards expansion of GCW and the influence of the eddies, represented by Vinciguerria lucetia; and a hypoxic habitat, represented by the highest abundances of Diogenichthys laternatus. Results are in contrast with previous studies that recorded these mesopelagic species throughout the water column. A third larval fish habitat was associated with the upwelling area off Cabo Corrientes, represented by Bregmaceros bathymaster. This species shows high tolerance to wide gradients of dissolved oxygen. Our records indicate that a highly stratified water column could favor the expansion of hypoxic StSsW and associated marine biota.