Vertical distribution of fish eggs and larvae in the Irish Sea and southern North Sea

Abstract

Fish eggs and larvae were analysed from 63 vertically stratified plankton hauls in the Irish Sea and southern North Sea. The dominant species were sprat (Sprattus sprattus), dragonet (Callionymus spp.), dab (Limanda limanda) and to a lesser extent rockling species, sandeel (Ammodytes spp.), whiting (Merlangius merlangus) and flounder (Platichthys flesus). There was little difference between species in the vertical distribution of either eggs or larvae. Most were concentrated in the upper 50 m of the water column, eggs in progressively increasing numbers towards the surface and larvae with a sub-surface peak at a depth of 10–15 m. The vertical distribution of eggs extended deeper in the water column than larvae, possibly due to some combination of eggs being spawned deeper and their passive susceptibility to turbulent mixing. There were no significant differences between day and night distributions and under mixed or isothermal conditions.