The effect of recent changes in the North Sea mackerel fishery on stock and yield

Mackerel, Scomber scombrus L., occur on both sides of the North Atlantic, restricted to the continental shelf regions. On the eastern side, mackerel occur from the Bay of Biscay to northern Norway. In this region two main spawning grounds have been de­fined, one in the North Sea and one in the Celtic Sea. In accordance with this, two m ajor stocks probably exist in the region. One has its distribution centre in the central N orth Sea and the other in the area south of Ireland (Anon., 1974).
The present paper deals with aspects of the biology, stock structure, and exploitation of mackerel in the ICES statistical areas IlI a and IV, with special re­ference to the North Sea stock.