Distribution and size of Antarctic krill (Euphausia superba Dana) in Polish commercial catches taken in the Atlantic sector of the Southern Ocean from 1997 to 1999
The distribution and internal structure of commercial krill concentrations were investigated in the areas of the South Shetland, Elephant, South Georgia and South Orkney Islands in the spring and summer from 1997 to 1999. The density of concentrations varied with area and season. The densest concentrations were found near the South Shetlands. Concentrations at night were several times less dense than those observed during the day. Between February and April the density of concentrations increased, while in May and June it decreased. From February to June the period of daylight becomes progressively shorter, therefore it must be assumed that there are factors other than daylight which have an impact on the density of krill concentrations. The internal structure of concentrations was very diverse, and mean density varied from 11 to 31 370 specimens per 1 000 m3. At night, krill concentrations were scattered throughout the water column, however no clear evidence of vertical migrations was found. Between February and April concentrations occurred in much shallower waters at night than during the day, while in May and June they occurred at the same depths at night as during the day or sometimes even deeper. Between February and April concentrations during the day were found in shallower waters, while between April and June they were found in deeper waters. The size structure of the krill varied during all periods and in all areas, however krill size was observed to decrease as the season progressed.