Winter distribution of macroplankton and micronekton in Masfjorden, western Norway

Abstract

Masfjorden was investigated as a potential site for sea ranching of cod. The macroplankton and micronekton were studied in order to reveal the distributional patterns of species and biomass during winter. The biomass was dominated by the mesopelagic fishes Benthosema glaaale and Maurolicus muelleri, the pelagic shrimps Pasiphaea multidentata and Sergestes arcticus, and the euphausiid Meganyctiphanes norvegica. All species performed die1 vertical migrations. B. glaciale was almost exclusively found in the deepest locations (>400 m). M. muelleri was found throughout the fjord, but large individuals were most common at one of the deep stations. The shrimps were mainly confined to the deeper parts of the fjord, where the 2 species were prominent in separate basins. The largest individuals were found at the deepest locations. The distribution of M. norvegica seemed to be unrelated to the topography. There was a marked maximum of euphausiids at the head of the fjord; these were probably advected into the fjord system. The total standing stock of macroplankton and rnicronekton was estimated to be 19.5 tonne ash-free dry weight. We conclude that the amount of macroplankton and micronekton present in Masfjorden does not provide a food resource on which several hundred thousand codlings could rely during winter