Between 1980 and 1997 British Antarctic Survey carried out 11 cruises in the region of South Georgia. Here we summarize the length-frequency distributions of krill caught on each of these cruises and look particularly at differences between krill taken from the eastern and western ends of the island. Cluster analysis revealed that the length-frequency distributions could be grouped into 5 main types with relatively simple biological characteristics: cluster 1 were medium-sized year 2+ krill (mean size 39.7 mm); cluster 2 were a mixture of year classes (mean size 37.7 mm); cluster 3 were large krill probably 3+ and older (mean size 49.5 mm); cluster 4 and 5 were small krill, mostly year 1 + either with or without some older size classes (mean sizes 27.2 and 24.5 mm respectively). Principle components analysis (PCA) provided good separation of these clusters using the first two axes (80 % of the total variance). The PCA for all cruises combined showed that there were no obvious differences in the type of krill found in different water depths, although there were some indications that differences did occur between different water masses. Detailed inspection of the individual cruises revealed firstly that the smallest krill were found in Weddell Sea water and that the length-frequency distributions at the western end of the island contained more large krill that those from the eastern end of the island. We consider such differences may arise because krill may originate from either the Weddell Sea or Bellingshausen Sea, may experience different conditions during transport to South Georgia and at either end of the island.
Numéro du document:
Point(s) de l'ordre du jour