BIRTH-DATE ANALYSIS AND ITS APPLICATION TO THE STUDY OF RECRUITMENT OF THE ATLANTO-IBERIAN SARDINE SARDINA-PILCHARDUS

The ages of 217 juveniles from the Atlanto-Iberian sardine (Sardina pi lchardus) stack were determined by means of counts of daily growth rin gs in otoliths. These juveniles were caught by the commercial purse-se ine fleet off Galicia (NW Spain) between June and November 1992. The b ack-calculated hatching period was 13 December 1991 to 2 April 1992, w ith a mean date of 2 February and a standard deviation of +/- 17 days. The original aim of the study was to relate the birthdate distributio n of the recruits to environmental, biological, and physical data take n during a series of oceanographic cruises. Oceanographic cruises, car ried out between March and July 1992, covered the spring-spawning area of the stock (Cantabrian Sea and coasts of Galicia, the supposed area of origin for the recruits) but such a relationship was not documente d because the results of the study showed that most surviving juvenile s were spawned before the period considered during the oceanographic c ruises. However, the observed birthdate distribution of the recruits, together with hydrographic data, does suggest that a larval drift from the northern Portuguese coasts to the Galician coast took place. Thus , at least in 1992, there is evidence to suggest that the winter-spawn ing zone, located along the coast of northern Portugal, may have been the area of origin for recruits off Galicia, in contrast to the previo us assumption that these fish were spawned in the Cantabrian Sea.