Life history of Calanus finmarchicus in the Norwegian Sea in relation to planktivorous fish

This paper is focused on the potential impact of planktivorous fish in shaping the life history of Calanus finmarchicus in the Norwegian Sea. It is suggested that seasonally migrating fish species influence the timing of spawning and descent, and hence the number of generations of C. finmarchicus annually, and that the presence of resident mesopelagic fish influences the selection of winter habitat. C. finmarchicus ascends from overwintering and starts spawning 1-2 months prior to the spring bloom, which is exploited by the developing copepodites. Mortality risks increase upon arrival of fish on their oceanic feeding migrations, which for herring is prior to the spring bloom. Spawning early in the season may therefore reduce parental risks of exposure to such predators. Late-stage copepodites are heavily exploited by seasonally migrating fish during summer, so representing a driving force for the seasonal descent of C. finmarchicus. Overwintering takes place below the main domain of mesopelagic fish. (C) 2000 International Council for the Exploration of the Sea.