Mackerel is a pelagic fish that can swim at great speeds and which in summer and autumn moves in huge shoals along the coast of Norway and into Skagerrak, the North Sea and the southern parts of the Norwegian Sea. In Europe, the mackerel family is divided into two main stocks: one living to the west of the British Isles and the other living in the North Sea and Skagerrak. The mackerel fished in the North Sea, Skagerrak and the Norwegian Sea generally belong to the western stock of mackerel. In spring, mackerel has a low fat content, whereas mackerel caught in the autumn may contain as much as 30% fat and thus also a large supply of omega-3 fatty acids. Mackerel is also an excellent source of vitamins D and B12.