Distribution and transport of Fish larvae at the entrance of the Gulf of California (September, 2016)

Fish larvae distribution and transport of dominant species were analyzed at the entrance to the Gulf of California in September 2016. Using the Sea Surface Temperature (SST) gradient, a frontal system was defined at the entrance to the Gulf. The most relevant gradient (∼0.06 °C km⁻¹) in the region was transverse to the gulf axis (W-E), from south of Cabo San Lucas to the mainland, south of the Pescadero Basin. This SST gradient was associated with an anticyclonic flow (∼0.4 m s⁻¹) that was connected with a cyclonic eddy outside the Gulf. Fish larvae of mesopelagic species such as Vincigueria lucetia and Benthosema panamense were widely distributed and increasing in abundance from north to south, while the mesopelagic Bregmaceros Bathymaster and the pelagic Auxis spp. showed an inverse abundance gradient. Most of these larvae were absent from the zone of strong SST gradient. A Lagrangian particle tracking model applied at the sampling stations where the fish larvae were collected, showed that during the first 5 days of trajectory, the transport was weak. But for the next 5 days, most of the particles were trapped by mesoscale flows that dominated the region. An unexpected result was that no particles crossed the transverse front, coinciding with the absence or low abundance of larvae there. The particles near to this front were transported west out the Gulf. We concluded that when the mesoscale flows are extended along the transverse axis of the Gulf entrance, these might trap inert particles and zooplankton organisms with little mobility, such as fish larvae in early phases of development, preventing their transport along the Gulf parallel axis (NW-SE), and therefore, affecting the species distribution.