Modelling the advection of herring larvae in the North Sea

Abstract

THE number of fish at the age of first capture in a fishery (recruitment) is dependent on the production of eggs by the parent stock and the survival of early life stages (eggs, larvae and juveniles). In many pelagic fish species the survival of larvae depends on transport from spawning to nursery areas1. To investigate larval transport processes for North Sea herring (Clupea harengus L.) we have modelled in three dimensions the advection of autumn-spawned larvae during the winter of 1987-1988 and compared the results with sequential field data on the actual distribution of larvae. Circulation in the North Sea is pre-dominantly wind-driven during the winter, and in 1987-1988 anomalous atmospheric conditions caused a reduction in cyclonic circulation and unusual transport of larvae from northern North Sea and west of Scotland spawning areas. Predicting variations in recruitment in advance of fishery legislation has always been difficult and the collapse of North Sea herring populations during the mid-1970s is believed to have been due to a period of several years of low recruitment coupled with high fishing activity2. Our results suggest that a better understanding can be achieved with the aid of environmental modelling.