Comparative study of spatial distribution patterns of the early stages of anchovy and pilchard in the NW Mediterranean Sea

Anchovy and pilchard are the most abundant pelagic species in the NW Medite rranean Sea, They spawn in different seasons, subject to different environm ental conditions: anchovy in summer, when the water column is stratified; p ilchard in winter, when the water column is vertically homogeneous. Tbe spa tial distribution patterns of eggs and larvae of these 2 species are compar ed in relation to the main productive features in the region during their r espective spawning seasons, The study was performed on the continental shel f off the Ebro River (NW Mediterranean) during June (for anchovy) and Febru ary (for pilchard), Sampling comprised a horizontal survey, designed to loc ate patches of eggs or larvae, followed by a Lagrangian experiment using st ratified hauls to study the vertical distributions at different times of da y in the water parcel tracked. While pelagic eggs and larvae of both specie s were present in the upper 70 rn of the water column, we recorded differen ces in the preferential vertical distribution and migration patterns. Maxim um concentrations of anchovy eggs and larvae were located in the upper 20 m ; pilchard concentrations extended down to 10-40 m. Vertical displacements by the larger larvae at night occurred in both species, but with opposite p atterns: anchovy larvae tended to aggregate in the upper 10 m, pilchard lar vae exhibited greater dispersal at night, with a preference for levels belo w 30 m.