Krill biomass and distribution variability in Subarea 48.3 in June 1991

Temporal and spatial variability of krill distribution features was investigated at the micropolygon of 8 x 6 miles, where eight consecutive hydroacoustic stations were carried out. Krill aggregations occurred as fields of small swarms of spatial distribution features (size and density of swarms, swarm field density, number of swarms per one mile) varied considerably from tack to tack within each survey. Horizontal extension of swarms amounted to 120 m, however about 70% of swarms were of 30 m in length, with density up to 200 g/m3. About 75% of all swarms revealed bad biomass of less 1 t. Average statistical parameters of swarms at polygon varied insignificantly from survey to survey, while the swarm number varied within the broad range from 1918 to 7000 and further to 1554 units. Krill biomass at polygon varied spasmodically within the range from 1091 to 6085 t. Krill distribution variability revealed at polygon suggests the impulsive nature of krill enter and exit out of the polygon due to its transport by the current. Besides, in the upper layer of 0-50 m the swarm number was a almost constant, and krill redistribution due to transport and diurnal migrations occurred in the layer of 5-150 m. Estimated velocity of krill swarms displacement corresponds to the estimated water transport velocity at the polygon, suggesting the passive krill transport occurred. Krill biomass transported across different tacks also varied spasmodically from survey to survey.