First evidence of a new spawning stock of Illex coindetii in the North Sea (NE-Atlantic)

Global changes drive abundance and distribution of species worldwide. It seems that at least some cephalopod stocks profit from global changes as indicated by increases in biomass and/or expansion of their geographical distribution, as appears to be the case for the commercially important ommastrephid squid Illex coindetii, in the North Sea. Based on the recently increased abundance of this species seen in research trawl hauls, here we present the first evidence of a summer spawning stock of Illex coindetii in the North Sea and derive a description of its life cycle. Neither mated females nor spent males were reported from the area previously. In quarter 1 the majority of Illex coindetii were immature (maturity stage 0) and maturing (maturity stage 1–3) while in quarter 3 almost exclusively mature and spent individuals (maturity stage 4–6) were caught. We observed up to three spermatangia bundles attached to females in quarter 3, indicating that spawning and reproduction takes place in the North Sea and that the species is already established in this area. Estimated egg hatching dates suggest a prolonged hatching period and therefore likely a long spawning season, although cold temperature seems to limit year round reproduction. The intensity of individual migrations from adjacent waters into the North Sea is unknown and therefore the number of individuals staying permanently in the North Sea could not be estimated. It is consequently still unclear whether the North Sea individuals of I. coindetii constitute a new separate stock.