Comparison of krill density estimated with swarm-based and dB-difference method using acoustic data collected by Chinese fishing vessel participating in the 2019 Area 48 survey

To address the effect of various identification methods on krill biomass estimates, comparison on the swarm-based and dB-difference (Sv_120kHz-Sv_38kHz) identification method were made using the acoustic data collected around the South Shetland Islands in Subarea 48.1 by the Chinese fishing vessel F/V Fu Rong Hai during the 2019 Area 48 survey. Identification window of swarm-based template were set to four ranges including [-20 20], [2 16], [0.4 12] and without dB window (only 120kHz used). Identification window of dB-difference method were set to [2 16] and [0.4 12] respectively. Distributions of estimated krill densities were statistically compared using significance test and geometric linear regression. Pairwise comparison indicated that there were significant differences among biomass estimated from various identification methods, except for the estimates from [-20 20] identification window and without dB window (only 120kHz used). Geometric linear regression analysis also confirmed the same conclusion.