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Acoustic visualization of large scale macroplankton and micronekton distributions across the Norwegian shelf and slope of the Norwegian Sea.

Melle, Webjørn; Kaartvedt, Stein; Knutsen, Tor; Dalpadado, Padmini; Skjoldal, Hein Rune
Working paper
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CM_1993_L_44.pdf (4.298Mb)
URI
http://hdl.handle.net/11250/105194
Date
1993
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  • ICES CM documents authored by IMR scientists (1949-2011) [3138]
Original version
This report is not to be cited without prior reference to the authors  
Abstract
We present results from acoustical (38 kHz split beam) surveys, biological

sampling (trawling, zooplankton nets), and measurements of physical

parameters (salinity, temperature, currents) across and along the shelf off

Norway (62-70°N). Major recurrent structures were apparent both

geographically and with time. Off the shelf, two deep scattering layers

prevailed; one of 50-100 m thickness where the upper border by day

fluctuated between 100 and 200 m depth, and one located deeper between

300-500 m. The upper layer was mainly composed of mesopelagic fish

(Maurolicus muelleri) and krill (Meganyctiphanes norvegica), while the

lower layer consisted of krill (Meganyctiphanes norvegica), mesopelagic

fish (Maurolicus muelleri, Benthosema glaciale), shrimps (Sergestes

arcticus, Pasiphaea multidenta), and jellyfish (Periphylla periphylla).

During winter, these two layers roughly comprise 95% of the

backscattering volume (biomass) in the upper 500 m. The shallow layer

partly intrudes onto the continental shelf, where the bottom topography

exerts strong impact on its distribution.

In June/July an additional scattering layer was apparent in the upper 20-30

m throughout most of the study area, though integrated backscattering

biomass varied by a factor of 50. In the south the layer was associated with

water masses of salinity <35 (i.e. with coastal characteristics). Further north

the layer was found off the shelf in water with stronger oceanic

characteristics as well. Hydrographic features indicated that coastal water

and biomass was transported off the shelf in connection with gyres over

the banks. Trawl catches showed that this structure was composed of 0-

group herring, fish (mainly seith), and krill. Backscattering volume was

positively correlated with abundance of 0-group herring caught in trawl,

but was not correlated with the meso-zooplankton biomass (mainly

Calanus finmarchicus), or other components of the trawl catches. The lack

of positive correlations between acoustic backscattering volume, and

biomass from net and trawl samples probably reflected differences in

selectivity of the sampling methods.
Publisher
ICES
Series
ICES CM Documents;1993/L:44

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