Inter-annual variation of Antarctic krill (Euphausia superba) density around the South Shetland Islands during 2013–2019

The Antarctic Peninsula region has long been recognized as an important habitat for Antarctic krill (Euphausia superba) and has served as a primary krill fishing ground over the last two decades. However, the in-field observation of krill biomass in this region was relatively rare during the last decade. From 2013 to 2019, a Chinese krill fishing vessel conducted five annual acoustic surveys around the South Shetland Islands during austral summers. These surveys revealed an overall increasing trend in krill biomass density, with the lowest estimate as 18.6 g m−2 (CV = 31.4%) in March 2015 and the highest estimate as 70.6 g m−2 (CV = 15.9%) in February 2019. The spatial distribution of krill swarms exhibited high inter-annual variability and strong heterogeneity. Over 40% of the distance intervals (1 n. mile) across all years showed krill densities of <10 g m−2. While fewer than 20% of intervals registered krill densities of 100 g m−2 or higher, these dense swarms contributed over 50% of the total krill biomass, strongly indicating that a significant proportion of krill biomass is driven by large, dense swarms. This study provides the most recent multi-year data on krill biomass distribution in the Antarctic Peninsula region and highlights the valuable role of fishing vessels in monitoring krill stock dynamics.