9 Zooplankton-fish interactions in the Barents Sea

Abstract

The Barents Sea is a high latitude ecosystem characterized by high variability. There are large interannual variations in ice cover, spring phytoplankton bloom dynamics, zooplankton stocks, and fish recruitment. The Barents Sea is an important feeding area for commercial fish stocks such as cod (Gadus morhua), capelin (Mallotus villosus) and herring (Clupea harengus). The fish resources in the Barents Sea have shown large changes during the last two decades. The stock size of capelin, which usually is the major planktivorous fish in the Barents Sea, was 4–8 million metric tons during 1973–1983. Due mainly to recruitment failure, a severe decline in capelin biomass (to below 0.5 million tonnes) occurred in the mid-1980s and mid-1990s. Predation by young herring on capelin larvae is regarded as the main cause of the recruitment failure of capelin in the Barents Sea; thus, periods of high abundance of young herring (year classes 1983 and 1991–1992) were followed by periods of low capelin abundance. As capelin are a key species of the Barents Sea ecosystem, the collapse of the stock caused food shortages for higher trophic level populations such as cod, harp seals, and guillemots.