A model study of the large-scale transport of fish eggs in the Kattegat in relation to egg density

A process-oriented model, with high vertical resolution, has been used to investigate variation in the transport of fish eggs and early larvae in relation to egg density. The main focus is on gadoid eggs from the spawning grounds in the southern Kattegat. Additionally, transport from the neighbouring areas, the central Kattegat and Oresund, is presented. The model results clearly indicate that transport is dependent on the egg density; lighter eggs are transported northwards whereas heavier eggs are to a larger extent retained or transported southwards. This study suggests that optimum densities in order to promote retention in the southern Kattegat are in the range of 1023-1026 kg m(-3). Observations from 2005 and 2006 of the vertical distribution of gadoid eggs combined with hydrographical data indicated high concentrations of eggs at the upper part of the pycnocline at densities of 1017-1022 kg m(-3). Combining the observations and modelling results on amount of dispersal and retention, suggests that gadoid eggs are mainly retained in the southern Kattegat (although shifted from maximum retention density) and simultaneously dispersed northwards. Even though the results of the study are described in the context of gadoid eggs, the results are applicable for other marine species with pelagic stages and buoyant particles within the tested density range.