Stocks of krill in the southern part of the Drake Passage and in the Bransfield Strait were estimated by the hydroacoustic method, during the BIOMASS-FIBEX expedition (Febr.-March 1981). Krill stocks in the Drake Passage and Bransfield Strait were assessed at about 1.2 and 2.3 mln tons, respectively. A map of krill distribution in these regions was prepared. The main krill biomass (66%) was found to occur within the Bransfield Strait which accounts for only 13.7% of the total area under survey.

Results of hydroacoustic investigations of krill biomass carried out in the South Shetland Island region between October 1986 and January 1987 are presented. A considerable difference in the krill biomass between Antarctic spring and summer was recorded. Initially observations were conducted close to Elephant Island, in the period just after the retreated of compact ice cover. Krill then aggregated only in swarms, the density of which frequently exceeded 100 t nM-2 . In the region of Polygon I (30—31 October 1986) the total estimated biomass was 26899 t, in the region of Polygon II (6—10 November 1986) it was 25827 t. Investigations were repeated in January 1987 obtaining 112372 t in the Bransfield Strait and 390309 t in the region of Elephant Island. The results are presented in tables and maps.

Results of hydroacoustic investigations of krill swarms occurring southwest of Elephant Island carried out between 30 October and 5 November 1986, are presented. Krill swarms of the geometric length of 32 m, mean vertical cross section area of 206 m2 , and mean density of 133 g m-3 were recorded and measured. Biomass distribution is presented in maps. The highest density values amounting to 5001 nM-2 were recorded in the eastern part of the survey area, above the slope of Elephant Island's shelf. On the basis of upper and lower limits of the occurrence of given krill swarms, a scheme of their vertical, diurnal distribution was constructed.