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

The distribution and transport of paralarvae of the complex Sthenoteuthis oualaniensis - Dosidicus gigas (“SD complex”, Cephalopoda: Ommastrephidae) in the tropical-subtropical convergence off Mexican Pacific were analyzed under contrasting interannual conditions. Two warm-ENSO years were sampled (2010 and 2016), in which the STT anomalies varied between 1 and 3 ºC in the whole study area, while during cold-ENSO year (2012) the STT anomalies varied between -2 and 0 ºC. The abundance of SD complex paralarvae was also contrasting between the ENSO phases. During warm-ENSO years the abundance drop to 2 org 1000 m^-3 concentrating around Cabo Corrientes, where the thermocline was relatively shallow (<60 m). During the cold-ENSO condition, the abundance rise to 84 org 1000 m^-3 and the paralarvae were present in all the sampled area, in the Gulf of California entrance, in a very shallow thermocline (<20 m). In both contrasting conditions the paralarvae were distributed in well stratified waters (>80 cylces h^-1). The statistical model confirm that the thermocline depth was one of the strongest predictors of the paralarvae presence. In addition, the transport model suggested association of the SD complex paralarvae with mesoscale structures that generate stratification, in which the eggs and hatched paralarvae had an appropriate habitat for nursery, retaining the paralarvae near the zone favorable for their posterior recruitment in a ~100 km radius, while extreme events can transport paralarvae as far as 500 km southeast of the spawning zone. The mesoscale activity promotes paralarval retention, and then an inferred survival. But the environmental context of the ENSO phases was a key component of the magnitude of the paralarval success.