Biomass of Antarctic krill (Euphausia superba) in the eastern Indian sector of the Southern Ocean (80–150°E) in the 2018–19 austral summer

•Data from a calibrated echosounder and biological sampling were used to estimate Antarctic krill biomass.•The survey was conducted in the eastern Indian sector of the Southern Ocean in the 2018–19 austral summer.•Biomass was estimated as 4.325 million tonnes.•Biomass of krill was similar between day and night. Biomass of Antarctic krill (Euphausia superba) in the eastern Indian sector of the Southern Ocean (80–150°E, corresponding to the longitudinal range of CCAMLR Division 58.4.1) in the austral summer of 2018–19 was estimated using data from a calibrated echosounder and biological sampling. This study was carried out as a part of the multidisciplinary ecosystem survey (KY1804) by Japanese research vessel Kaiyo-maru. The krill biomass was estimated using an up-to-date standard method of CCAMLR, the “swarm-based method”. Biomass of krill in the area had not been estimated since 1996 (BROKE survey). KY1804 covered a total of 4680 km of the surveyed distance in the surveyed area of 0.909 million km2. Krill were mainly distributed between the Southern Antarctic Circumpolar Current Front and the Antarctic Slope Front. The krill biomass during KY1804 was estimated as 4.325 million tonnes (CV = 17.0%), comparable with the 1996 BROKE estimate (4.83 million tonnes, CV = 17.0%); however, direct comparison is difficult because of differences in (1) biomass estimation methods; (2) timing of the surveys (KY1804 commenced about 40 days earlier in the year than BROKE); and (3) areal coverage, primarily because of different positions of the sea ice edge, especially in the western part of the area. There was no noticeable difference of krill biomass between day and night. This study provides a 2018–19 biomass estimate for Antarctic krill in the eastern Indian sector of the Southern Ocean, which is a basis for studies of this species as well as the Southern Ocean ecosystem.