Euphausia superba (Antarctic krill) is a key component of the South Georgia (SG) ecosystem, supporting important populations of higher predators including seabirds, seals and whales. It is also the focus of a commercial fishery, which operates exclusively during winter. However, little is currently known about the distribution or abundance of krill or krill predators during this period. To address this, three ecosystem surveys were carried out during the austral winter of 2022 along the northern shelf of South Georgia, undertaken in May, July and September, to correspond with the start, middle and end of the typical krill fishing season. These surveys included assessing krill abundance and distribution using acoustic and net methods. Cetacean and seabird observations were also carried out on all surveys following JNCC Seabird at Sea Team (SAST) methods, with more detailed distance sampling and passive acoustic monitoring of cetaceans carried out during July. Simultaneously, the movements of gentoo penguins from two locations on the northern shelf were tracked with PTT and GPS tracking devices.
Krill areal biomass in the area normally used by the krill fishery (Eastern Core Box (ECB)), using combined day and night transect data, was 268,521 tonnes in May, 249,822 tonnes in July and 76,828 tonnes in September. Krill density was 45.3 g m-2, 42.1 g m-2 and 13.0 g m-2 over the same period. Distinct diurnal variability in biomass was observed, with significantly higher biomasses detected at night in July and September. The most frequently-sighted whale species were humpback and southern right whales, with fin and blue whales demonstrating a more offshore distribution. Gentoo penguins remained almost entirely over the continental shelf, spending 83.5% of their activity within 30km of the coast, and demonstrating little evidence of direct overlap with the area occupied by the fishery.
Our combined observations supported a hypothesised westerly movement of krill throughout the winter period with predator distributions closely linked to that of krill.