On the problem of diurnal migrations of some fish species on the South Georgia shelf (Subarea 48.3)

The results of experiments on the South Georgia Shelf carried out in the period of 1986 to 1990 have been presented. Six (6) daily stations were occupied where vertical distribution of fry and young individuals (including adult specimens) of Champsocephalus gunnari, Champsocephalus aceratus, Pseudochaenichthys georgianus (Channichthiidae family) and Nototheniops larseni (Nototheniidae family) was studied. The most representative data were obtained for Ch.gunnari and N.larseni. The vertical migration trend was the most distinctive in Ch.gunnari fry. The individuals used to ascend towards the water column before the sunrise, being finished their return migration before the sunset. Juvenile and adult individuals were found in the pre-bottom layer by day, being presented their small quantities in the water column, including the superficial layer, at night. N larseni fry vertical migration pattern was poorly expressed during 24 hours. It was distinctly observed in juvenile and adult individuals: they were kept close to the bottom by daylight and were not caught within the pre-bottom layer. At night (after the sunset) they ascended into the water column where they were found in the superficial layer. No substantial variations in middle size fry of both species were found at different depth levels during 24-hour periods. Ch. aceratus fry were found within the whole water column during 24-hour periods, being mainly observed within two lower depth levels. Juvenile and adult individuals were kept by day close to the bottom and within the whole water column at night. However major catches were taken within the limits of the pre-bottom depth level, being higher as compared to those taken by day. Ps.georgianus fry were caught during 24-hours nearly in equal quantities in the pre-bottom layer by day and at higher depth levels at night. Juvenile and adult individuals were almost not found in the day-time, being observed within the whole water column at night and mainly caught within the pre-bottom layer.