Migration of adult mackerel along the Atlantic European shelf edge from a tagging experiment in the south of the Bay of Biscay in 1994

Within the frame-work of the Shelf Edge Fisheries Oceanography Study (EU AIR SEFOS Project), 10 000 mackerel were tagged in March and April 1994, off the Basque Country (Spain), at the eastern part of ICES Division VIIIc, close to the boundary between the, so-called, Southern and Western mackerel stocks in the north-east Atlantic. The purpose of this experiment was to outline the migration routes for mackerel spawning in the south-east corner of the Bay of Biscay and to examine the justification for separating a Southern and Western stock. Recaptures were recorded along the western coasts of Europe, from the north-west of Spain to the Norwegian coast. These results connected the fisheries of the southern and north-western areas and put in doubt the existence of two separate stocks in these regions. The paper concludes that the fishery on spawning mackerel that takes place in the east and central Cantabrian sea in the first half of every year is made on mackerel coming from the north-western area extending their southward spawning migration through ICES Division VIIIc, before going back to north. This migration pattern provides a simple explanation for the strong seasonality of the southern fisheries on adult mackerel and for the disappearance of those adults from that area during the second half of the year.