Desk study on the transport of larval herring in the soutern North Sea (Downs herring)

Current understanding about the drift and behaviour of larval herring is reviewed with particular emphasis on the Downs herring and the development of a model for larval transport. Downs herring are the component of North Sea herring that spawn in the southern North Sea and English Channel. Generally the larvae of the Downs herring drift east towards the German Bight and Skagerrak, but this is dependent on the meteorological forcing of local hydrography. Whilst it has been possible to model the broad trajectory of the larvae, modelling the yearly variability in drift patterns has proved difficult. The drift of the larvae and past-larvae does take them close to the Dutch coast in some years (as shown by survey results). It is during this phase of their life cycle (from larvae to metamorphosis) that the strength of the recruiting year class is determined. The larvae show vertical migration as they grow and also begin to aggregate after metamorphosis. There is no evidence in the primary literature for triggers for directional movement (such as salinity or depth of water column) . There is no work published to date, on the impact of anthropogenic disruption of larval drift on the productivity of Downs herring or on the fishery.