In the Greater North Sea the main forage fish (herring, sandeel, sprat, and Norway pout) feed mainly on plankton and are an important food source in the foodweb. Smaller piscivorous fish (e.g. whiting Merlangius merlangus, haddock Melanogrammus aeglefinus, and grey gurnard Eutrigla gurnardus) and stocks that enter the North Sea only in specific seasons such as western horse mackerel Trachurus trachurus and mackerel, all eat forage fish and juvenile gadoids to a large extent. Benthic-feeding fish include all kinds of flatfish feeding on prey on or near the bottom. Fish that can eat large fish (>25 cm) are mainly large cod, saithe, and elasmobranchs, but species like seals and harbour porpoise are also important top predators. Trends in fishing pressure and stock size are presented in the ‘Selective extraction of species’ section. Natural mortality is now the main source of mortality for many commercial species due to a successful reduction in fishing mortality in recent years.
Threatened and declining fish species in the Greater North Sea according to OSPAR: