Seasonal dynamics of an Antarctic krill resource hot spot in the Bransfield Strait, Antarctica

ABSTRACT Objective Antarctic krill Euphausia superba is an important species in the Southern Ocean ecosystem. Understanding the trends and variability of the krill biomass is critical for understanding the three-way interactions between resources, krill-dependent predators, and fisheries, particularly given the recent concentration of fishing activities in specific areas. The purpose of this study was to enhance our understanding of the seasonal dynamics and potential influence of environmental factors in a krill resource hot spot in the Bransfield Strait. Methods Based on acoustic data that were collected by krill fishing vessels during the 2012/2013 to 2021/2022 fishing seasons, this study used statistical bootstrapping to identify a perennial hot spot of krill at the Bransfield Strait. The data for catch per effort were also analyzed to corroborate the trends that were observed in the acoustic data. Additionally, a correlational analysis was conducted to determine the relation between the physical environment and krill density. Results The results suggested that krill biomass exhibited seasonal dynamic variation, characterized by substantial monthly increases from austral summer to autumn. The local scale of the krill biomass in the hot spot during autumn could be several times greater than that estimated from acoustic transect surveys for the entire Bransifield Strait stratum in summer. The data for catch per effort supported the trend of monthly variability. Krill were found to be concentrated mainly in sea areas with temperature ranges of −1°C to 1.5°C and flow velocities <0.05 m/s. The position of oceanic fronts and the properties of water masses strongly regulated the seasonal variation in krill density. Conclusions The study identified a perennial krill hot spot in the Bransfield Strait that is characterized by significant seasonal variation in biomass. The findings highlight the importance of specific environmental conditions in regulating krill density and suggest that understanding these dynamics is crucial for managing krill fisheries and protecting krill-dependent predators.