DIEL VERTICAL MIGRATIONS OF MEGANYCTIPHANES-NORVEGICA IN THE KATTEGAT- COMPARISON OF NET CATCHES AND MEASUREMENTS WITH ACOUSTIC DOPPLER CURRENT PROFILERS
F. Buchholz et al., DIEL VERTICAL MIGRATIONS OF MEGANYCTIPHANES-NORVEGICA IN THE KATTEGAT- COMPARISON OF NET CATCHES AND MEASUREMENTS WITH ACOUSTIC DOPPLER CURRENT PROFILERS, Helgolander Meeresuntersuchungen, 49(1-4), 1995, pp. 849-866
Diel vertical migration of a stable and well-defined population of Nor
dic krill, Meganyctiphanes norvegica (Crustacea, Euphausiacea) was inv
estigated during eight days in August 1989, in the Laso-Deep, East of
the Danish island Laso. Net catches with a multi-net (MOCNESS) and mea
surements with a moored and a shipboard Acoustic Doppler Current profi
ler (ADCP) were compared; Backscattered energy as a measure for biomas
s gave good correlations to the dry weight of M. norvegica and smaller
zooplankton from net catches. Diel migratory patterns matched well, a
s determined, parallel with both methods. Migratory vertical velocity
was determined with ADCP at 2-3 cm sec(-1). The potential for the use
of ADCPs for biological investigation is discussed. Vertical migration
was dependent on environmental parameters. The krill did not cross a
temperature barrier of 14 degrees C, although rich food sources were s
ituated beyond it. Differences in salinity did not play a role. Curren
ts were involved in plankton distribution. Light was an important Zeit
geber (synchronizer) and determined the density of the krill aggregati
ons. Feeding behaviour did not interfere with the light-induced migrat
ory pattern of Nordic krill at the Laso-Deep.