An updated census of southern elephant seals Mirounga leonina at South Georgia using satellite imagery

Historically, South Georgia supported the largest breeding population of southern elephant seals Mirounga leonina globally. Yet since 1995, this population has remained largely unassessed and was presumed to be stable. Here, we provide an updated assessment of this sub-Antarctic population and demonstrate the application of sub-meter resolution satellite imagery as a valuable approach for censusing an extensive, remote, and challenging breeding population. Across two breeding seasons, 2024 and 2025, we tasked satellite imagery with resolutions between 0.3 m and 0.5 m and integrated image-based counts with extrapolative modeling under a generalised additive framework to estimate abundance at unobserved beaches. Using this approach, we estimate 107,630 (95% CI: 93,945 – 123,342) breeding females at South Georgia, compared to the historical benchmark of 113,444 (se = 4,902) in 1995. This corresponds to a total population of 376,705 individuals (95% CI: 328,808 – 431,697). However, this should not be interpreted as evidence of population stability. The present census followed the spread of highly pathogenic avian influenza through the sub-Antarctic and therefore reflects a recently perturbed population, while methodological differences between surveys and limited validation of the satellite correction framework also affect direct comparability with the 1995 census. In light of the recent IUCN re-assessment of southern elephant seals as Vulnerable, our results highlight both the importance of renewed population assessment at South Georgia and the value for tracking population trajectories across remote Southern Ocean breeding sites.