Distribution of the Early Larval Stages of Cod, Plaice and Lesser Sandeel across Haline Fronts in the North Sea

A number of commercially important fish species spawn in the coastal areas of the North Sea in the late winter, including cod (Gadus morhua), plaice (Pleuronectes platessa) and lesser sandeel (Ammodytes marinus). The distribution of the early stages of these species overlap to some extent, suggesting that adult spawning and dispersal of eggs and larvae are influenced by the same hydrographic features. The present study describes the results of a field survey in March 1997 which covered concentrations of small larval cod, plaice and lesser sandeel in the central and southern North Sea. The goals were to ascertain the major traits of larval distribution patterns and the spatial correspondence among species, focusing on the relationship between larval distributions and hydrographic characteristics. Larvae of all three species were found distributed within the shallow Regions of Freshwater Influence (ROFI), predominantly in the Dogger Bank and German Bight areas. There was a high degree of overlap between the distributions of cod and plaice, while the maximal abundance of lesser sandeel was found inshore of the other species. Larval distributions were to a large extent confined by the frontal zones between freshwater-influenced water masses and shelf water of the central North Sea, and larval abundances peaked in the vicinity of the haline fronts.