Distribution and some biological features of icefish (Champsocephalus gunnari) at different life cycle stages in the South Georgia subarea

The results of icefish ecology were summarized for the period of above 20 years of South Georgia Subarea study. Ecological aspects were considered taking into account temporal-spatial variability. The functional structure of Ch.gunnari distribution area was described on the basis of juvenile fish distribution at different stages of physiological state. Juvenile fish mainly distribute in the south, immature fish - in the cast and southwest, while adult at the north of the shelf. It was revealed that the life mode changed from pelagic one occurring at early life stages, to near-bottom - pelagic one after 20 cm length reaching and the bottom one at length above 40 cm. Ch.gunnari undertakes vertical migrations: young fish above 4 cm in length distribute within 75 cm from the bottom, and migrate into the less depths in the day-time and to the bottom at night. Immature fish distribute in the water column for the most time and is fished with midwater trawl. Its diurnal migrations pattern is similar to that of the larger fish. Diurnal migrations of adult fish are opposite to those of juveniles: it migrated to the bottom in the day-time and into the water column at night. Mature fish form dense aggregations near the bottom where it is fished with bottom gears. The annual cycle of fish is subdivided into 3 periods: feeding (October-March), spawning (April-June) and wintering (July-September). Feeding migrations of fish above 25 cm in length occur in the northern shelf and associate to migrations of krill being the main, food item of icefish. Two major directions of prespawning migrations were revealed: from the north-east to coastal areas in the northern and north-eastern part and to the open shelf areas in the southeast, while in the north-west part it migrated westwards and south-westwards. Post-spawning migrations had the opposite direction. Overwintering of icefish occurred at the depths of 200-250 m far from the coast mainly northwards of the Island.