Sardinella aurita and Engraulis encrasicolus are two co-occurring clupeoid species whose spawning season takes place in summer in the NW Mediterranean, their eggs and larvae coexist in the plankton during this period. The summer is characterised by a stratified water column and low primary production at surface, where the only nutrient supply comes from runoff water. Spawning of both species is associated to these productive areas, and larval growth and survival would depend on hydrodynamic structures dominated by the Northern Current. The current flows over the continental slope and significant mesoscale features such as meanders and eddies are being developed along the current path. These structures may act as areas of accumulation, offering suitable conditions for larval survival, or as offshore exporting mechanisms. Three oceanographic cruises, consisting of basic oceanographic parameters measures and icthtyoplankton sampling, were performed in summer (July 2003, July 2004 and June 2003) along the Catalan coast. Larval growth rates of both species, studied by analysing their sagittal otoliths, were established as 0.604 mm day-1 for E. encrasicolus and 0.775 mm day-1 for S.aurita. With these values the age of sampled individuals and larval abundances at age were obtained. Then, global larval mortalities for each survey were estimated by log-linear regression of the abundances at age. S. aurita presented a much higher daily mortality rate (46%) than E. encrasicolus (28%). For a given area, the model compares the actual age distributions with that which would be obtained if the population were in a steady state, assuming the mortality rates within the age range used for the regression are constant for each species and survey. This balance model allows to estimate the larval inputs and outputs in the area, thus assessing how the hydrodynamic structures influence the survival of E. encrasicolus and S.aurita larvae

43 Annual Larval Fish Conference, 21-24 May 2019, Palma, Balearic Islands

Peer Reviewed