Seasonal changes in the diet of the Atlantic mackerel from the north-east Atlantic in ICES Division VIIIc during the period 1988–1999. The diet of juvenile (21–29 cm) and adult mackerel (30–45 cm) in this area in spring (the spawning season) and autumn varied in composition and size of prey. In spring, the average prey weight was 0·009 g and the number of prey was 180 individuals per stomach, with the average stomach content volume being 1·62 g (0·60% BW [body weight]), and 1·50 g (0·51% BW) when considering the empty stomachs. In autumn, the average prey weight was 0·28 g, the average number of prey per stomach was 17, and the average stomach weight that contained food was three times higher than in spring, and 2·3 times when considering the empty stomachs. In spring, the diet of the juveniles consisted of euphausiids, crustacean larvae and other zooplankton, whereas euphausiids formed 90% of the diet in the adults. In addition, during this period mackerel were cannibalistic, feeding on their own eggs. In autumn, the juveniles ate hyperiids and other, mainly gelatinous zooplankton, whereas for the adults blue whiting were clearly important, since they comprised 90% of the stomach weight.