Effects of a mesoscale eddy on the distribution of mesopelagic fish larvae in the Gulf of California

We examined the effect of a mesoscale cyclonic eddy on the three-dimensional distribution of Vinciguerria lucetia and Diogenichthys laternatus in southern Gulf of California during July 2010. CTD data and zooplankton samples collected with a closing-opening net (505 μm), were obtained on 2 transects across the eddy, and on a transect outside of the mesoscale structure. In the later the thermocline depth was at ~40 m where larvae V. lucetia dominated. Opposite to V. lucetia distribution, D. laternatus larvae was the dominant species in the deepest strata. In the area influenced by the cyclonic eddy (~350 m depth and ~60 km diameter), the thermocline was sunk from ~25 m (eddy edge) to ~50 m depth (eddy center). The isotherms below the thermocline formed a dome from ~350 m to ~100 m depth in the eddy center. This upwelling coincided with an increase of D. laternatus larvae in the water column. Compared with the transect outside of the cyclonic eddy, the shoaling of the isotherms inside the eddy produced not only an increase of D. laternatus larvae, also decreased the V. lucetia abundance. These variations in larval distribution of both mesopelagic species are closely correlated with the mesoscale cyclonic eddy.