The effect of differences in the methodology used for the CCAMLR 2000 krill acoustic survey and the 2019 synoptic survey were considered. These were 1) the effect of acoustic surveying at night, 2) differing trawl selectivity between the vessels that participated in the survey, and 3) the effect of krill discrimination method. Surveying during the day only produced a 6% increase in the standing stock estimate and the trawl selectivity between vessels had minimal effect on the krill length distributions. The choice of krill discrimination method had a marked effect on the per-stratum biomass estimates. Areas with most of the krill backscatter in well-defined schools were least sensitive to the choice of discrimination method.
Dr Gavin Macaulay (Norway)
Dr Odd Aksel Bergstad (Norway)