Variations in zooplankton volumes at the permanent oceanographic stations along the Norwegian coast and at weathership station M(ike) in the Norwegian Sea during the years 1949-1972

Abstract

During the years 1949-1972 zooplankton was sampled in vertical hauls at permanent oceanographic stations along the coast of Norway and at the weathership station "M" in the Norwegian Sea. During 1949-1962 (station M:-1965) Nansen net "8/72" was used, later the Juday net, J.36. The Juday net was found to catch more plankton in relation to the opening of the net. During May-August average plankton volumes were larger off northwestern Norway than farther south. Deviations from the long term averages in plankton volumes were compared with observations from adjacent areas of the North Sea, Norwegian Sea and Barents Sea. Some similarities were found, but local variations seem to be the major cause of observed differences. No clear relationship was established between zooplankton biomass and sea temperature. Rich year classes of cod seem to be born more frequently in years when zooplankton biomass is above average, while medium and poor year classes are possibly more frequent in years with lower abundance of plankton, but the data are not sufficient for a conclusion. No correlation was found between abundance of plankton and of cod larvae.