LIFECO: Predatory interaction between fish species and top-down control of zooplankton relative to frontal processes

The secondary production and standing stocks of zooplankton in frontal systems may be controlled by planktivorous predators, i.e. juvenile but also adult planktivorous fish as well as gelatinous zooplankton known to concentrate in frontal areas. This predation pressure may become too high to sustain favourable feeding and growth conditions for competing juvenile fish over longer periods. High abundances of zooplankton and juvenile fish in frontal regions lead to an aggregation of planktivorous as well as piscivorous predators.

These results in increased predation pressure on fish larvae and O-group fish, counteracting potentially enhanced feeding conditions and higher growth rates in frontal regions. General knowledge about the food composition exists for most important demersal fish species in the North Sea and Skagerrak systems and to some extend also for their pelagic O-group stages. However, with respect to the coupling of hydrographic features, prey availability and feeding behaviour, data are almost completely missing.

Information on the diet composition of important pelagic and planktivorous predators/life stages (e.g. mackerel, horsemackerel, saithe, gelatinous predators), which are hypothesised to have a strong impact on the recruitment process of many North Sea fish species, are only fragmentary.