Variability in Overwinter Antarctic Krill Transport Pathways and Connectivity in the South-West Atlantic Sector of the Southern Ocean

Antarctic krill are central to the Southern Ocean ecosystem and support a commercial fishery. Late larval stages of Antarctic krill depend on sea ice for food and shelter during winter. As climate change alters sea ice habitats and polar ecosystems, understanding krill transport and retention is essential for ecosystem-based fishery management. These late-stage larvae have been observed to perform reverse diel vertical migration (DVM), moving from beneath the sea ice during the day to the upper water column at night. Variability in ocean currents and sea ice drift, together with behaviours such as DVM, can strongly influence krill transport and retention. To investigate the impact of this behaviour, we conducted Lagrangian particle tracking experiments using 32 years of daily sea ice and ocean velocities from a 0.1° global ocean–sea ice model (ACCESS-OM2-01). Virtual particles were released in the south-west Atlantic sector of the Southern Ocean and tracked over winter (April–October), a key period prior to spring recruitment. To assess sensitivity to DVM, we applied five scenarios in which particles spent different proportions of each day influenced by ocean currents and sea ice drift under sea ice. Transport driven solely by ocean velocities resulted in the highest proportion of particles on the Antarctic Peninsula shelf by winter's end, with low interannual variability (55.5% ± 7% of released particles). Increasing exposure to sea ice drift reduced shelf retention and increased variability (33.6% ± 10.9%). Our results show that including sea ice interactions enhances overwinter connectivity from the Antarctic Peninsula to South Georgia and between management areas, highlighting sea ice-driven northward transport of young krill. As krill depend on declining sea ice habitats, connectivity across the Antarctic Peninsula and Scotia Sea may shift in the future. Understanding interannual transport variability between fishing regions improves stock assessment and supports sustainable management.