On the causes of the recruitment failure of herring in the central and northern North Sea in the years 1972-1978

Abstract

An analysis of stock and recruitment data for individual North Sea herring stocks shows that the recruitment failure in the 1970s cannot be completely ascribed to a low spawning-stock size. Other explanations, such as selective removal of juvenile herring by the industrial fishery for sprat, or increased competition from other species, are also shown to be incompatible with various data presently available. A new hypothesis presented here ascribes the recruitment failure to a disruption of the transport of herring larvae, caused by a change in North Sea circulation. Results from an international Isaacs-Kidd Midwater Trawl sampling programme, together with data from a sampling programme for herring larvae in Dutch coastal waters, are presented to support this hypothesis.