THE SPAWNING ENVIRONMENT OF THE BAY OF BISCAY ANCHOVY (ENGRAULIS-ENCRASICOLUS L)

The spawning season of the Bay of Biscay anchovy population extends fr om March to August, although most of the reproductive effort is made d uring May-June. Spawning is triggered by the warming up of surface wat ers and coincides with the maximum rate of temperature rising and the onset of stratification. Preferential sea surface temperatures are in the range of 14 - 18 degrees C. This population shows a relatively sho rt peak spawning period that seems to be an adaptation to stable and p redictable environmental conditions in the SE Bay of Biscay. At the be ginning of the spawning season, usually in April, anchovy concentrate in the SE corner of the Bay of Biscay. Later, in May, anchovy spawning is prevalent in the SE Bay of Biscay. As the spawning season progress es, in June. distinct coastal and oceanic spawning areas appear. Simul taneously, the geographic range of spawning extends north and westward s. The Bay of Biscay anchovy selects stable habitats related to river plumes, shelf edge fronts and oceanic eddies, where increased biologic al production potentially occurs. i) There are low salinity plumes rel ated to main river estuaries (Gironde, Adour and Bidasoa); ii) structu res related to shelf break fronts - French shelf to the North of 45 N and southern Bay of Biscay-; and iii) oceanic eddies of slope waters ( SWOD-DIES), in oceanic sites outside the continental shelf. The popula tion shows a density-dependent selection of the spawning habitat. The spawning areas associated with the Estuaries of Gironde, Adour and Bid asoa, in the SE region of the Bay of Biscay, seem to form a refuge bas in favourable to the maintenance of this population of anchovy even in adverse environmental conditions.