Krill distribution and biomass variability within Subarea 48.3 in June 1991

Temporal and spatial variability of krill distribution characteristics was investigated in an 8 x 6 mile micropolygon, where eight consecutive hydroacoustic surveys were carried out. Krill aggregations occurred a s fields of small swarms whose spatial distribution characteristics (size and density of swarms, swarm field density, number of swarms per mile) varied considerably from tach to tack within each survey. The maximum horizontal extension of swarms was 120 m, although about 70% of swarms were of 30 m in length, with density up to 200 g/m3. About 75% of all swarms revealed biomass to be less than 1 tonne. Average statistical parameters of swarms in the polygon varied insignificantly from survey to survey, while the swarm number varied within the board range from 1 918 to 7 000 and further to 1 554 units. Krill biomass in the polygon varied spasmodically within the range from 1 091 to 6 085 tonnes. Krill distribution variability revealed in the polygon suggests an irregular import and export of krill from the polygon due to transport by the current. Additionally, in the upper layer of 0 to 50 m swarm number was almost constant, and krill redistribution due to transport and diurnal migrations occurred in the layer of 50 to 150 m. Estimated velocity of krill swarm displacement corresponded to the estimated water transport velocity in the polygon, suggesting that passive krill transport occurred.