Mögliche Ursachen des geringen Heringsnachwuchses in der Nordsee

Though the stocks of North Sea herring seemed to have recovered from small numbers since the mid-1990s we do recently observe a new decline in the spawning stock biomass. This is mainly caused by four consecutive years of small reproduction. Whilst the adults produce enough eggs and larvae only few survive until mature stages. The reasons for the bad recruitment are not clear. In this paper we investigate the influence of climate conditions, in particular the North Atlantic Oscillation (NAO) that obviously triggers the interaction between the size of the spawning stock and the abundance of larvae. We show that approximately 60 % of the recruitment variance can be explained by specific constellations of spawning stock size and climatic conditions. Beside physical factors we also discuss several working hypotheses shedding light on the influence of biological variables on the fluctuation of herring offspring.