Scale of variation in Antarctic krill abundance at the South Orkney Islands (Subarea 48.2): insights from multi-scale acoustic surveys during summer 2016

The South Orkney Islands (Southwest Atlantic; Subarea 48.2) is a region where Antarctic krill and krill-dependant predators are highly abundant and the commercial fishery now operates intensively. Understanding krill temporal-spatial distribution and ecosystem dynamics in the region is important for assessing appropriate krill acoustic survey designs, and for devising small-scale fisheries management units that are relevant to local foraging predators. In this study, we quantify krill abundance and its spatial-temporal variation at the South Orkney Islands using acoustic survey data collected at different spatial scales along the northern shelf-break in January-February 2016. Overall, we found that the view of the spatial distribution and the abundance of the local krill population varied substantially between different scaled surveys (~500, 3000, 8500 and 28,000 km²) that were undertaken with approximately the same timeframe (within ~10 d). Our study highlights that important concentrations of krill occur to the northwest of the South Orkneys that have high spatio-temporal variability. The study also highlights the difficulty in monitoring such a dynamic krill population effectively within reasonable logistical and practical survey constraints, and demonstrates that the level of variation in local krill distribution and abundance needs to be considered in fisheries management and wider ecosystem studies.