Distribution and abundance of Antarctic krill (Euphausia superba) off EastAntarctica (80-150 degrees E) during the Austral summer of 1995/1996

A hydroacoustic survey was conducted in the waters off East Antarctica (CCA MLR Division 58.4.1) during January to March 1996 to estimate the biomass ( B-omicron,) of Antarctic krill Euphausia superba). The krill biomass in the area surveyed (872,500 km(2)) was estimated to be 4.83 million tonnes with a CV of 17%. Dense aggregations of krill, although encountered infrequentl y, dominated the biomass estimate. At least 97% of these aggregations were less than 200 m in transected length, and the largest was 1 100 m. Large cl usters of aggregations ( > 1 km in transected length) were encountered on 4 of the 18 transects, and these dominated the krill biomass encountered dur ing the survey. Krill were more abundant, with a broader latitudinal distri bution, in the west of the survey area (80-115 degrees E) than in the east (115-150 degrees E). The absence of krill and the presence of warmer oceani c waters characterized the northeastern sector of the surveyed area. Krill aggregations were most frequently encountered in the shelf break region whe re the summer ice edge, 1000 m isobath, and the Antarctic Slope Front (ASF) (associated with the cooler coastal and warmer oceanic waters) coincided. The majority of krill aggregations were found in the top LOO m of the water column, and when deeper ( > 100 m) aggregations occurred they were usually coincident with aggregations in the top 100 m. The mean krill density for the area surveyed was 5.54 g m(-2) consistent with previous observations th at the Indian Ocean sector is relatively impoverished when compared with kr ill density values for the South Atlantic. This density is at the low end o f the range of values reported for surveys around South Georgia, Elephant I sland, and the adjacent Prydz Bay region. However, this low average biomass results from averaging over a few krill-rich areas with large areas where krill is scarce or absent. (C) 2000 Elsevier Science Ltd. All rights reserv ed.