Evidence of sociality and group foraging in Antarctic minke whales (Balaenoptera bonaerensis)

Top krill predators such as the Antarctic minke whale (AMW) serve a vital role within the fragile Antarctic sea-ice ecosystem. They are an abundant krill specialist, but their ecological role in the Antarctic remains poorly understood due to their cryptic behavior and remote habitat. It is therefore crucial to develop a baseline understanding of their basic social and foraging ecology. This study uses animal-borne camera tags to quantitatively explore these critical ecological aspects. Twenty-eight tags were deployed on AMW between 2018 and 2019 in Andvord and Paradise Bays around the Western Antarctic Peninsula. Tag data were analyzed with respect to diving, foraging, and social behavior. Results suggest the presence of loose fission-fusion sociality, with individuals forming short-term associations in 60.6% of cases including both foraging and non-foraging contexts. Socializing was significantly more common for larger individuals and resulted in a significant decrease in foraging rates for both shallow ( 30 m) dives. There were 12 instances of simultaneously tagged individuals that associated with one another in pairs or trios, displaying synchronized spatial movement and diving behavior. These data illustrated the use of group foraging strategies, with high incidence of synchronized foraging dives (67.5% of associated dives) and lunges (64% of associated lunges). Our results provide clear baseline information on AMW sociality and group foraging, which will help direct future studies for more targeted work. This study will improve our ability to understand the relationship between Antarctic species and their environment as climate change continues to alter the ecosystem landscape. Significance Baseline information on sociality is thus key to understanding broader species ecology, which is especially important for keystone species. Our study is the first to directly provide these foundational insights for AMW, a common krill predator in the Antarctic sea-ice ecosystem. Individuals displayed short-term associations in a fission-fusion social structure similar to other baleen whale species, and socializing was associated with both larger individuals and lower foraging rates. In simultaneous tag deployments, tagged individuals frequently associated with one another and displayed synchronized diving and foraging behavior. Our results suggest that sociality may be more important to minke whale ecology than previously thought. These results p