Mesoscale activity in the northeastern pacific water mass convergence region and its influence on fish larvae distribution by development stages (October 2022)

Abstract

Based on satellite, hydrographic, and zooplankton data, the mesoscale activity, and its effect on the three-dimensional distribution of fish larvae in the northeastern Pacific water mass convergence region off Mexico during October 2022 were analyzed. Three eddies were observed during the cruise, but two were measured. An anticyclonic eddy (not crossed by the cruise) was observed by satellite data in the mouth of the Gulf of California. It formed off Mazatlán in Transitional Water and moved southeast of Cabo San Lucas. It was the smallest (10,207.4 km) and least energetic (140.7 cm2s−2) of the eddies. A parallel sampling transect to this eddy showed predominance of fish larvae in preflexion stage in the surface mixed layer with dominance of Benthosema panamense and Syacium ovale species (epi-mesopelagic and soft-bottom demersal species). A second anticyclonic eddy had formed about a month earlier in the Tropical Surface Water when this was measured. Its trajectory showed that it came from the mainland coast off Cabo Corrientes. It was the most energetic (216.6 cm2s−2) and presented the maximum anomalies of temperature (7.4 °C) and Dissolved Oxygen (>50 μmolkg−1), due to the downwelling that it produced (up to 95 m depth). It was also associated with the highest concentration of fish larvae (231.3 larvae100m−3) from ∼200 m depth to surface, observing dominance of larvae in flexion stage of B. panamense and Bregamaceros bathymaster (coastal neritic species). This eddy could also retain and transport species of soft-bottom demersal habits (Dormitator latifrons). One cyclonic eddy, located off Cabo San Lucas had California Current Water. It was the largest (26,032 km2) and oldest forming about nine months earlier off mainland coast in front of Pabellones Cove. Due to the upwelling of deeper water (up to 530 m depth), the minimum anomaly values of temperature (−5.8 °C), salinity (<−0.5 gkg−1) and Dissolved Oxygen (<−50 μmolkg−1) were present. Low abundance of species such as Vinciguerria lucetia and Diogenichthys laternatus (both epi-mesopelagic) in the postflexion stage were presented there. Results showed that mesoscale eddies affected the three-dimensional fish larvae distribution in different ways. This could broaden the vision of the mesoscale evolution of physical-biological interactions in the oceans.