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Marine Ecology Progress Series

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MEPS 190:253-262 (1999)  -  doi:10.3354/meps190253

Vertical migration behaviour in the northern krill Meganyctiphanes norvegica is influenced by moult and reproductive processes

G. A. Tarling1,*, J. Cuzin-Roudy2, F. Buchholz3

1Scottish Association for Marine Science, PO Box 3, Oban, Argyll PA34 4AD, Scotland, UK
2Observatoire Océanologique, UPMC CNRS INSU LOBEPM, Océanographie biochimique et Ecologie, BP 28, 06230, Villefranche-sur-Mer, France
3Biologische Anstalt Helgoland, Stiftung AWI, Meeresstation, Postfach 180, 27483 Helgoland, Germany

ABSTRACT: A population of the northern krill Meganyctiphanes norvegica was sampled between 24 July and 3 August 1998 in the Alkor Deep, Kattegat, in order to investigate the influence of sexual and developmental factors on the vertical distribution of adult krill. Depth-discrete samples of krill were taken with a 1 m2 MOCNESS net at the cardinal times of day (midnight, midday, sunrise and sunset). Specimens were immediately measured and categorised for moulting and spawning status. Further samples were preserved for detailed analysis in the home laboratory. Results showed that the population concentrated in the deep (80 to 100 m) during day-time but segregated vertically during night-time. Moulting occurred in the deep during night-time, away from the main part of the non-moulting population, which was located between 80 and 50 m. Spawning females were most evident in the uppermost depth interval (30 to 5 m). Moulting at night in the deepest layers may be viewed as a mechanism to avoid cannibalism whilst in a vulnerable condition. Spawning in the warm upper layers accelerates reproductive processes and may also reduce the depth to which the eggs sink before hatching into nauplii.

KEY WORDS: Northern krill · Euphausiids · Swarming · Diel vertical migration · Spawning · Moulting · Sexual behaviour

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