Ommastrephid squid paralarvae distribution and transport under contrasting interannual conditions in the tropical-subtropical convergence off Mexico

The distribution and transport of paralarvae of the complex Sthenoteuthis oualaniensis - Dosidicus gigas (SD complex, Cephalopoda: Ommastrephidae) in the tropical-subtropical convergence off Mexico were analyzed under contrasting interannual environmental conditions. Two El Niño years were sampled (2010 and 2016), in which the SST were up to 3 °C above the average throughout the study area, while during La Niña year (2012) the SST anomalies were up to 2 °C below the average. During El Niño years, a relative shallow thermocline (<60 m depth) was detected around Cabo Corrientes, where the paralarvae were found with mean abundance of 2 org 1000 m⁻³. During La Niña condition, a shallower thermocline was detected in the entrance of the Gulf of California (~20 m depth) and the paralarvae abundance rose to 84 org 1000 m⁻³ with high frequency of occurrence. In both El Niño and La Niña conditions the paralarvae were mainly found in the strongly stratified waters (>80 cycles h⁻¹). In addition, a simple dispersion Lagrangian model based on observed satellite geostrophic currents, suggested association of the SD complex paralarvae with mesoscale structures, in which the eggs and hatched paralarvae had an appropriate habitat for a nursery, retaining the paralarvae until their recruitment in a ~100 km radius. But during warm extreme events, with less mesoscale activity, the paralarvae could be transported as far as 500 km southeast of the spawning zone. Even though the interannual ENSO conditions modulate the magnitude of the paralarvae abundance, the shallow and well developed thermocline could help paralarvae to increase their survival chances, while mesoscale activity retains them near the productive coastal waters.