Influence of some physical and biological factors on the density and vertical distribution of Atlantic halibut Hippoglossus hippoglossus eggs

Abstract

ACT: Atlantic halibut Hippoglossus hippoglossus (L.) eggs were sampled using a Tucker trawl and a MOCNESS-sampler at 3 selected localities in North Norway. The specific density of the eggs was determined in a density-gradient column. The eggs were found to achieve higher specific density with increasing age. In areas with a horizontally stable, clearly defined pycnocline (Andfjord and Seraysund), the vertical distribution of eggs was characterized by a unimodal egg distribution. Furthermore, the older eggs were found at higher average capture salinities than younger eggs, i.e. they were distributed in relation to their neutral buoyancy. In an area with a horizontally more variable and less defined pycnocline (Malangen), the pattern of vertical distribution of eggs was less distinct, often with polymodal egg distributions. In this hydrographically variable system, no heterogeneity in the distribution of the various egg developmental stages could be discerned. In Malangen, thus, it is proposed that the vertical distribution of halibut eggs is most strongly influenced by physical factors.