We studied the population dynamics of Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus in Billefjorden, Svalbard (78°40′N). All three species reproduced in the fjord with different timing. The maximum abundance of Calanus spp. copepodite stages peaked on the 11th of July (29,000 ind m
−2). C. glacialis was the dominant species accounting for 60–80% of the total Calanus abundance. C. finmarchicus appear to thrive in the fjord despite the low temperatures (−1.86°C to 5°C) and accounted for 20–30% of the total population. C. hyperboreus contributed less to the total abundance (5–20%). A 1-year life cycle is suggested for C. finmarchicus and C. hyperboreus in the fjord, C. glacialis has a 1- to 2-year life cycle. Highest mortality rates were observed for copepodite stage CV in C. finmarchicus and C. glacialis (0.09 and 0.075 d
−1, respectively) and for females in C. hyperboreus (0.149 d
−1). Mortality of copepodite stages was substantially lower in C. glacialis than in the other species. This is particularly obvious in the early and numerous copepodite stages (CI + CII) during the period of recruitment to these stages. This suggests that differences in secondary production in Arctic pelagic ecosystems are controlled partly by population loss rates.
