A review of variability in the distribution and abundance of Norwegian spring spawning herring and Barents Sea capelin

The historic data on the fisheries on Norwegian spring spawning herring and Barents Sea capelin show that the migration pattern and time of spawning have changed for these species. Furthermore, modern techniques like tagging, hydroacoustic abundance estimation and virtual population analysis have shown that the abundance, both of the adult and the immature parts of the population, fluctuates widely. Predators (other fish, seabirds, sea mammals) of pelagic fish must have experienced corresponding fluctuations in food availablilty.