Seasonal distribution of the cephalopod Alloteuthis subulata in the central and southern North Sea

Alloteuthis subulata was monitored in the waters of the central and southern North Sea from 1991 to 1998 as part of the International Bottom Trawl Surveys. More than 90% of all cephalopods encountered belonged to A. subulata, which species thus should be considered the dominant cephalopod in the southern North Sea. Migration patterns appeared to be entirely determined by water temperatures. During autumn and early winter, juvenile animals migrated from the cooling southeastern coastal waters to the deeper, in winter relatively warmer, waters of the central North Sea. In spring, the young adults migrated back to the warming shallow coastal waters along the Danish, German, Dutch, Belgian and southeastern British shores. After spawning in these waters, most of the adults died. The life cycle of A. subulata proved to be largely or entirely confined to the central and southern North Sea, and the species should therefore be considered a permanent inhabitant of these waters.