Abstract: The abundance of krill on the continental shelf and slope north of the Antarctic Peninsula was measured during the 28th Chinese Antarctic Research Expedition in the summer of 2011–2012. Acoustic data for the estimation of krill abundance were collected using an EK500 scientific echo sounder installed on the R/V Xuelong, using a 38 kHz operating frequency. However, the data were affected by significant electrical noise that had to be removed before integrating the mean volume backscattering strength (Sv). Noise correction and signal-to-noise-based thresholds were used for post-processing removal of noise from the acoustic data. Cell-size parameters of one ping and 70 samples were used to average the power data, a quantity equivalent to the Sv with no time varied gain applied. The signal-to-noise ratio (SNR) was defined as the original Sv minus the estimated maximal Sv_noise, such that 0 dB could be set as the minimum desired SNR. The results showed that the noise power averaged over all transects was −146.47 dB re 1W and the average noise-removal percentage reached 88.3%. The mean biomass and numerical density in the survey area were 27.30 g·m⁻² and 2.95 ind·m⁻²,respectively. This study demonstrates that the R/V Xuelong is a useful platform to study the biomass and distribution of krill using acoustic methods.

Key words: Antarctic krill, acoustic estimation, noise, signal-to-noise ratio