Seasonal relationships in biological parameters and in spatial distribution in the euphausiid populations sampled during the XIIIth and XVth expedition to the Ross Sea

This report summarises the results of krill studies from a large-scale surveys of the Italian Antarctic Oceanographic Cruises conducted in December 1997-January 1998 and January-February 2000. A midwater sampler-trawl (Hamburg Plankton Net) was used to collect zooplankton and fish larvae. Net samples data on Euphasiids were analysed at the aim of: 1) obtain a general picture of interannual and seasonal variability of distribution pattern and abundance of Euphausia superba and Euphausia crystallorophias in the western Ross Sea (Antarctica) in relation to ice cover. 2) Explore the population structure of E. superba and its possible spatial and temporal variations across the investigated area.
The present paper has demonstrated that, in the Ross Sea, during the late spring (1997-98), E. superba and E. crystallorophias had common spatial distribution. Juveniles of E. superba were concentrated in a delimited area in Shelf waters and in general, the maturity stage of this species increased with decreasing of latitude (from 76° to 71°S). On the contrary, during the summer period, the two species inhabited different areas and there weren’t particular spatial distribution patterns in the biological characteristics of E. superba.
For both the periods, the analysis of the biological parameters seems to indicate statistically significant differences in biological characteristics among the hauls (aggregations), while within each haul the parameters are homogeneous.