Multiple indicators suggest a scarcity of krill (Euphausia superba) at South Georgia in 2021

We report on a range of monitoring activities undertaken in the Scotia Sea in 2021. Based on evidence from multiple sources (acoustic moorings and survey, predator monitoring at Bird Island and Maiviken, commercial fishery and research trawls), it appears that Antarctic krill (Euphausia superba) were scarce in Subarea 48.3 for an extended period during much of 2021 but returned in November 2021. This follows similar anomalies in 1991, 1994, 1998, 2009 and 2016, all of which were indicated by breeding failure in gentoo penguins. The 2021 anomaly also resulted in the record lowest proportion of krill by mass (3%) in the diets of macaroni penguins in January and February 2021 and low krill abundance (12% by mass) in icefish diets in May 2021. We illustrate how the ecosystem effects of this anomaly progressed over time, manifesting at different times in different species. This may partially explain why the anomaly was not apparent from the Combined Standard Index (CSI) prepared by the CCAMLR Secretariat. The events observed in 2021 are consistent with the hypothesis that the South Georgia krill population is sustained by recruitment pulses which fail in some years. We discuss potential environmental drivers of these failures which will be explored in ongoing work.