Zooplankton reacts very sensitive on hydrographical changes which can be caused through climate change. Due to their sheer abundance, zooplankton communities are critical to the functioning of ocean food webs. The three Calanus- species Calanus finmarchicus (Gunnerus, 1765), C. glacialis (Jaschnov, 1955) and C. hyperboreus (Krøyer 1838) are the most important herbivores in Arctic seas in terms of species biomass. All three species are abundant in Fram Strait, the only deep connection between the Arctic ocean and the Northern Sea. For this study three stations (station 58, 80 and 82) in Fram Strait were compared regarding to the species composition of Calanus spp. and the developmental stages. The data was compared to the hydrographical conditions of each station. The mesozooplankton samples were taken with a multinet and the optical plankton recorder, LOKI (Lightframe on- sight key species investigation). The LOKI- data (750- 0 m) and the multinet samples (1000- 0 m) showed the biggest total abundance of Calanus spp. at station 80 (LOKI: 40. 073 and multinet 101. 376 [individuals*m-2]). Less abundance was found at station 82 (LOKI: 27. 710 and multinet: 83. 672 [Individuen*m-2]), followed by station 58 (LOKI: 12. 381 and multinet: 17. 248 [Individuen*m-2]). At station 58 both methods showed a similar distribution of the developmental stages, in which the most abundant developmental stage was the copepodit stage V. All species were most numerous in the upper 50 m of the water column where the highest fluorescence was found, too. C. finmarchicus was the most abundant species at all stations and was mainly found within the upper 50 m of the water column. The older developmental stages of C. glacialis (from copepodit stage IV on) and C. hyperboreus (from copepodit stage III on) occurred most frequently in deeper water layers. Station 58 was the only station where Polar surface water was found. At this station, many young developmental stages of C. hyperboreus were found. The results indicate a context between the distribution of the developmental stages and the species composition with the hydrographical parameters. High abundance was linked to high fluorescence. The overwintering- stages of the C. glacialis- and C. hyperboreus- population had already started to move towards deeper water layers for the diapause. Abundance of Calanus spp. at other stations (48 and 60) was much lower than the abundance at the stations 58, 80 and 82 of this study.