Selective Predation by Pelagic Arctic Char on Crustacean Plankton in Takvatn, Northern Norway, before and after Mass Removal of Arctic Char

Abstract

Abstract Arctic char Salvelinus alpinus once occurred at high densities in the pelagic zone of Takvatn. An intensive fish stock reduction program begun in 1984 reduced the catches of pelagic Arctic char by approximately 60% from 1981 to 1986. The crustacean plankton was dominated by Bosmina longispina, Cyclops scutifer, and Eudiaptomus graciloides. With the exception of a density increase of B. longispina, only minor changes were found in the density and species composition of the zooplankton after the stock reduction. Terrestrial insects and crustacean plankton dominated the diet of pelagic Arctic char in both 1981 and 1986. Cyclops scutifer was positively selected in June and July of both seasons. Following the density increase of B. longispina, this species was strongly selected in August–September. Other zooplankton species were either avoided or randomly selected.