Estimation of the biomass of krill in Prydz Bay during January/February 1991 and February/March 1992 using echo integration

Hydroacoustic surveys of the abundance of krill (Euphausia superba) in the Prydz Bay region were undertaken in January/February 1991 and February/March 1992.
The surveys indicated some association of krill with the shelf break in the western part of the survey area but also found that the shelf break was in general not a region of relatively high krill abundance. The mean surface density of krill in 1991 was 15.4 g/m2 and in 1992 was 7.4 g/m2 respectively. These densities are large compared to estimates of 1.95, 3.45 and 1.78 g/m2 for statistical areas 48.1, 48.2 and 48.3 (SC-CAMLR 1991, p47) but small compared to 20.2 g/m2 estimated for January 1985 from the Australian SIBEX-II data. The Australian SIBEX-II estimate falls in the middle of the range of densities estimated from seven reported surveys between 1981 and 1985 (Higginbottom et al. 1988). The biomass of krill in 3.5 milion km2 of the Prydz Bay region was estimated to be between 4.8 to 5.4 million tonnes in 1991 and between 2.2 and 2.6 million tonnes in 1992. The extent of bias in these results due to the presence of substantial biomasses of species other than Euphausia superba in the survey areas (Williams et al. 1983; Ikeda et al. 1984,1986; Hosie et al. 1988) could not be determined.