Abstract

The North Sea is a relatively small area characterised by different water masses based on physical and biological oceanographic characteristics, e. g., tidal mixing fronts, shelf break fronts and permanently mixed waters. These features provide an ideal opportunity to investigate the early life history of sprat. The aim of the present study is to examine the hypothesis that the growth rate of sprat (Sprattus sprattus) larvae varies with the oceanographic conditions. The physical oceanographic data examined include temperature, salinity and density, while the biological variables were chlorophyll a concentration and microzooplankton abundance. Highest larval abundance was associated with the tidal mixing front transect, however, the microzooplankton was less abundant here than in the other areas sampled. Using otolith analysis, the estimated growth rates of the larvae ranged from 0.362 to 0.404 mm per day during the reproductive peak in the North Sea. Statistical analysis of the growth rates from the different areas did not show any difference, despite a wide range of microzooplankton concentration and varying oceanographic characteristics. At the mixed side of the tidal mixing front in the German Bight, where larval abundance peaked, the growth rate was no different than in the other areas. These results confirm that there was no variation in growth rate in relation to food availability and oceanographic conditions in the eastern North Sea.