FISH larvae distribution and transport on the thermal fronts in the Midriff Archipelago region, Gulf of California

From a set of satellite and hydrographic data and zooplankton samples, effects of thermal fronts and mesoscale structures on the distribution and transport of fish larvae in the Midriff Archipelago Region (MAR) of the Gulf of California during a summer (June 2006) and a winter (February 2007) were analyzed. Using the Sea Surface Temperature (SST) gradient magnitude, a frontal system was defined in the southern part of the MAR during both periods. The most intense fronts (>0.08 °C km ⁻¹) originated at the convergence between cold waters from the continuous vertical mixing at the sills and basins and warm water of the southern Gulf of California. These fronts varied in their orientations, from near longitudinal in June 2006 to near transverse in February 2007, with respect to the axis of the gulf. The surface currents showed high occurrence of eddies associated with the sills and basins in the MAR. Fish larvae of the most abundant and frequent species, Benthosema panamense, Serranus sp. 1, Triphoturus mexicanus and Haemulon californiensis in June 2006, and Engraulis mordax, Leuroglossus stilbius, Sardinops sagax and Diogenichthys laternatus in February 2007 exhibited the highest larval abundance in both the strongest thermal fronts and the anticyclonic eddies observed over the southernmost basin. The exception was the E. mordax larvae, which were distributed in all the study area. A Lagrangian particle tracking model applied to the MAR domain showed high particle accumulation in the strongest fronts and eddies on the 7th and the 14th day in both periods. The connectivity matrixes showed retention of particles >70% in most cases, but in the sill area, there was transport from south to north in June 2006 (~30%), and from east to west in February 2007 (~30%). Results demonstrate that the interaction of the thermal fronts, independent of their position, and the mesoscale eddies may generate great accumulation of fish larvae, and possibly of other zooplankton groups, limiting transport between the northern and southern Gulf of California.