INVESTIGATIONS OF MOULT CYCLES OF THE ANTARCTIC KRILL EUPHAUSIA SUPERBA DANA IN CONCENTRATIONS IN THE D'URVILLE SEA (EAST ANTARCTIC) (Twelfth Symposium on Polar Biology)

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The krill (Euphausia superbd) collected with the commercial trawl in the D'Urville Sea (off the Terre d'Adelie) in late January-early April 1989 was investigated for the moult stages, sex, length and maturity stages. From each catch, 41-80 (58 on the average) specimens were examined for moult stages according to BUHHOLZ'S method with the identification of DRACH'S moult stages. Euphausia superba aggregating in concentrations appeared to be characterized by the specific phases of the moult cycle. Most of the animals were intermoult or early premoult stages regardless of the sex and age. The premoult krill may leave the aggregations before ecdysis (probably as swarms with synchronous moulting). Thus, the moult processes should strongly influence the size and density of the concentrations. In autumn the moult frequency decreased, so the krill in concentrations was mostly in the intermoult phases. A slow moult rate is connected with an increase of the aggregation density probably due to the decreased loss of the moulting krill or (and) moderation of the locomotor activity correlated with the moult state.