Krill of the Ross Sea: distribution, abundance and demography of &lt;i&gt;Euphausia superba&lt;/i&gt; and &lt;i&gt;Euphausia crystallorophias&lt;/i&gt; during the Italian Antarctic Expedition (January-February 2000)

Antonello Sala,Massimo Azzali,Aniello Russo

doi:10.3989/scimar.2002.66n2123

Abstract

Net samples data from the 15th Italian Antarctic Oceanographic Cruise (Jan-Feb 2000) were analysed to obtain a general picture of the summer distribution pattern, abundance and demography of krill in the western Ross Sea (Antarctica). A midwater sampler-trawl (Hamburg Plankton Net) was used to collect zooplankton and fish larvae. Mean relative biomass of Antarctic krill Euphausia superba , in the area north of Continental Shelf, was 9.3 g/1000 m 3 of filtered water with a mean density of 10.9 ind./1000 m 3 . Ice krill Euphausia crystallorophias replaced the Antarctic krill in dominance in the High Antarctic Zone (south of 74°), with a mean relative biomass of 3.0 g/1000 m 3 and a mean density of 19.1 ind./1000 m 3 . The present data have demonstrated that in the Ross Sea the two species of euphausiid inhabited different areas during the summer period. Oceanographic data indicate that both euphausiid species were found in surface waters, Euphausia crystallorophias in proper Ross Sea water, and Euphausia superba in Antarctic Surface Water. The catch data of Euphausia superba were characterised by the complete absence of larval stages, scarce occurrence of juveniles and composed primarily of large adult stages, whereas the overall length frequency distribution of Euphausia crystallorophias was characterised by a first mode of juvenile individuals and a second mode consisting of sub-adults and adults.

Highlights

IntroductionThe present paper analyses the catch data collected during the last survey in the Ross Sea (January–February 2000), to study the abundance, distribution and demographic parameters of the krill populations
The present paper analyses the catch data collected during the last survey in the Ross Sea (January–February 2000), to study the abundance, distribution and demographic parameters of the krill populations.Relatively few studies have concerned krill populations from the Pacific sector, and in particular in the Ross Sea
Oceanographic data indicate that both euphausiid species were found in surface waters, Euphausia crystallorophias in proper Ross Sea water, and Euphausia superba in Antarctic Surface Water

Summary

Introduction

The present paper analyses the catch data collected during the last survey in the Ross Sea (January–February 2000), to study the abundance, distribution and demographic parameters of the krill populations. Few studies have concerned krill populations from the Pacific sector, and in particular in the Ross Sea. In order to improve the krill knowl*Received March 22, 2001. Edge in the Ross Sea, the Italian National Project of Antarctic Research (PNRA) has supported acoustic surveys and net samplings since 1989. The 1989-90 survey was conducted in early summer (26 December 1989 - 25 January 1990), contemporary with the melting of the ice. Krill was sampled using the EZ-NET-BIONESS plankton net, KRILL OF THE ROSS SEA 123 with nominal mouth opening of 0.25 m2 (Guglielmo, 1992). The catches were insufficient for any demographic analysis because the net was not efficient in sampling adult stages of krill (

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Discussion

Conclusion