A new dynamic distribution model for Antarctic krill reveals interactions with their environment, predators, and the commercial fishery in the south Scotia Sea region

Summary

This study addresses a critical gap in understanding Antarctic krill distribution around the South Orkney Islands in the Scotia Sea—an area that has become the highest catch zone for krill fishing since 2019. Using ten years of acoustic survey data (2011-2020), researchers developed the first dynamic distribution model for this 850,000 km² region (CCAMLR Subarea 48.2). The model reveals where krill congregate, what environmental factors drive their distribution, and how fishing activity overlaps with areas used by krill-dependent predators like chinstrap penguins. The findings directly support CCAMLR's efforts to revise krill fishery management by providing the spatial data needed to allocate catches in ways that protect both the krill population and the ecosystem that depends on it. This research is particularly timely given the recent expiration of spatial catch allocation measures at the end of the 2023/2024 fishing season.

Key Findings

• Krill hotspots: The northern and eastern shelf edges of the South Orkney Islands consistently show the highest krill densities, with a notable concentration in submarine canyons at the northern shelf break

• Critical overlap zone: Intense fishing activity, high krill density areas, and chinstrap penguin foraging grounds all converge at the northern shelf edge—creating potential competition for resources

• Environmental drivers: Distance from shelf break, distance from summer sea ice extent, and salinity were the most important predictors of krill presence and density • Weddell Sea connection: High krill densities correlate with specific sea surface height values (−1.75 m) associated with Weddell Sea oceanographic features, supporting the hypothesis that the Weddell Sea acts as a transport pathway for krill into this region

• Climate influence: Positive phases of the Southern Annular Mode correlate with Weddell Sea features positioned closer to the South Orkney shelf and higher observed krill densities

• Interannual variation: Krill biomass and distribution showed high year-to-year variability, with 2012-2014 showing highest densities and 2015-2016 showing notably lower densities (possibly linked to the 2016 El Niño event)

• Model performance: The hurdle model explained 13.1% of deviance in krill presence-absence data and 12.1% in density estimates—modest but typical for highly dynamic pelagic species

• Management application: The spatial predictions from this model will be integrated into CCAMLR's risk assessment framework to inform spatial and temporal allocation of future krill fishing quotas

Abstract

The management strategy for the Antarctic krill (Euphausia superba) fishery is being revised. A key aim is to spatially and temporally allocate catches in a manner that minimizes impacts to both the krill stock and dependent predators. This process requires spatial information on the distribution and abundance of krill, yet gaps exist for an important fishing area surrounding the South Orkney Islands in the south Scotia Sea. To fill this need, we create a dynamic distribution model for krill in this region. We used data from a spatially and temporally consistent acoustic survey (2011–2020) and year-specific environmental covariates within a two-part hurdle model. The model successfully captured observed spatial and temporal patterns in krill density. The covariates found to be most important included distance from shelf break, distance from summer sea ice extent, and salinity. The northern and eastern shelf edges of the South Orkney Islands were areas of consistently high krill density and displayed strong spatial overlap between intense fishing activity and foraging chinstrap penguins. High mean krill density was also linked to oceanographic features located within the Weddell Sea. Our data suggest that years in which these features were closer to the South Orkney shelf were also years of positive Southern Annular Mode and higher observed krill densities. Our findings highlight existing fishery–predator–prey overlap in the region and support the hypothesis that Weddell Sea oceanography may play a role in transporting krill into this region. These results will feed into the next phase of krill fisheries management assessment.

Published in

Limnology and Oceanography, 2025, doi: 10.1002/lno.12809

2025

Authors

Jennifer J. Freer, Victoria Warwick-Evans, Georg Skaret, Bjørn A. Krafft, Sophie Fielding, Philip N. Trathan

Institutions

British Antarctic Survey (Cambridge, UK) Institute of Marine Research (Bergen, Norway)

Methods

AcousticBiological sampling DataField

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