Antarctic seals and the sea-ice environment

The Antarctic sea-ice zone is a critical ecological region, acting as both breeding/molting and foraging grounds for ice-dependent species and as a vital winter habitat for subantarctic predators. Its high biological productivity results from processes such as seasonal sea ice retreat, growth of ice algae, and enhanced primary production in coastal polynyas. These processes sustain short, efficient food webs that are vulnerable to climate-driven changes, including sea ice decline and increased extreme weather events. To understand how top predators respond to these environmental shifts, this multidisciplinary project focuses on Weddell and crabeater seals as sentinels of ecosystem change, integrating long-term observation with innovative tools and approaches across five interrelated parts.

Part 1 – Long-term observatory and oceanographic monitoring (part of the SNO-MEMO):
We analyzed an 18-year dataset tracking Weddell seals before and after the 2010 calving of the Mertz Glacier Tongue, revealing persistent changes in diving behavior and foraging areas. However, long-term changes in oceanographic conditions have not yet been fully investigated. To address this, we will use seal-borne sensors that record temperature and salinity during winter dives to gain new insights into the evolving interactions between ocean and sea ice. We will continue the time series to monitor how the system changes over time. These combined datasets will provide a robust foundation for understanding long-term behavioral shifts and the environmental drivers shaping predator responses in a rapidly changing ecosystem.

Part 2 – Fine-scale foraging ecology and sea ice structure:
To complement long-term movement data, we use seal-borne micro-sonars to detect prey fields and estimate sea ice thickness. This high-resolution dataset refines our understanding of predator-prey interactions and the ecosystem structure under which foraging occurs. We will continue the work initiated in 2019 and 2022. The integration of Parts 1 and 2 enables us to link large-scale movement patterns with fine-scale ecological drivers, such as prey availability and ice characteristics.

Part 3 – Underwater vocal communication:
Seals’ behavioral responses to environmental change also include adaptations in communication. Building on prior aerial and underwater playback experiments (2023-2024), we now focus on underwater vocalizations between Weddell seal mothers and pups. Using acoustic tags and a 4-hydrophone array, we will explore the ontogeny and function of these calls. Coupled with behavioral data from Parts 1 and 2, this component will provide a more holistic understanding of how seals use sound to maintain social bonds and navigate their environment.

Part 4 – Crabeater seals and krill distribution:
Extending our scope to another key predator, we investigate crabeater seals and their foraging behavior in the Dumont d’Urville region-an area atypical for the species. This pilot study helps map krill distribution, a key prey species in the Southern Ocean. We will pursue the pilot study (first phase conducted in November 2022) on crabeater seals. The long-term goal is to document how these systems evolve over time and to predict the future of krill populations and their predators.

Part 5 – Ontogeny of foraging behavior in seal pups:
To link early-life behavior with long-term ecological patterns, we will monitor Weddell seal pups on their first trips at sea. This new component complements the long-term tracking in Part 1 and the individual behavioural variability observed in Part 2. By understanding the development of foraging strategies, we aim to identify early predictors of ecological success in a rapidly changing environment.

Together, these five integrated research streams create a comprehensive framework for assessing the ecological resilience of Antarctic predators. By combining long-term observational data with fine-scale ecological, acoustic, and ontogenic studies, the project aims to advance our understanding of how environmental change is reshaping predator behavior, prey dynamics, and sea ice-ocean ecosystems in the Southern Ocean.