Population structure of icefish (Champsocephalus gunnari)
in the South Georgia area (Antarctic)

The living conditions of Champsocephalus gunnari in the eastern, western shelf areas of South Georgia and at Shag Rocks are different. The length-age structure of C.gunnari groupings inhabiting the areas at Shag Rocks and South Georgia is characterized with the lack of fish below 11 cm in length and older than 6-7 years (10-11 years in the South Georgia area) and considerably lower number of large fish above 40 cm in length in catches. These distinctions are the result of a certain geographic isolation of the area. On the basis of the cluster analysis the similarity of icefish up to 22 cm in length has been revealed in the western and Shag Rocks groupings and differences between those and the eastern grouping both in otolith morphology and morphometric characteristics. In larger fish the similarity between the eastern and western groupings and the differences between those two and Shag Rocks grouping appears. These differences increase with fish length. The analysis of all data available allows to assume the common origin of the western and Shag Rock groupings. C.gunnari of two-three years old (at the length of 22-23 cm) migrate from the South Georgia area and remain at Shag Rocks. Icefish reaching 40-43 cm in length either die or return to the Island. The results obtained provide the basis to assume with a high probability that C.gunnari population in the South Georgia area is the major reproductive unit of the area distributing currently near the Island, while the shallow Shag Rocks area is a zone of the life space extension or the feeding zone.