New research findings from the British Antarctic Survey (BAS) paint an alarming picture: On the subantarctic island of South Georgia, the number of breeding female elephant seals declined by 47 percent between 2022 and 2024, an unprecedented drop. The cause is an outbreak of the highly pathogenic avian influenza HPAI H5N1, which has been spreading rapidly across the region since late 2023.
The results of the study, published in Communications Biology, are particularly significant because the South Georgia population is considered the world’s largest aggregation of southern elephant seals and includes more than half of all reproductive animals. Long regarded as stable and well-protected, the colony is now experiencing dramatic losses.
Declines of up to 60 Percent in Individual Colonies
The research team used modern aerial imaging technology to monitor the island’s three largest breeding colonies, which together represent 16 percent of the entire female breeding population. Comparing the numbers before and after the outbreak reveals the scale of the impact: On average, 47 percent of the females were missing, and in some colonies the decline exceeded 60 percent.
Dr. Connor Bamford, seal ecologist and lead author of the study, expressed deep concern: “The scale of this decline is truly shocking. In typical years we see fluctuations of about 3 to 7 percent, but losing nearly half of the breeding population is unprecedented. This corresponds to roughly 53,000 missing females across South Georgia.”
A Long-Lived Giant Under Pressure
Southern elephant seals are among the most impressive marine mammals of the Southern Ocean. They dive up to 1,500 meters deep and travel thousands of kilometers in search of food. Their numbers on South Georgia had been considered stable for decades.
But the emergence of avian influenza in September 2023 marked a dramatic turning point. Initially detected in skuas, the virus soon spread to marine mammals, with devastating consequences for elephant seals and Antarctic fur seals.
“The situation is especially concerning because these animals are long-lived,” explains Dr. Bamford. “Even short-term declines in reproduction or survival can have long-lasting effects on population stability. The consequences of this outbreak will likely be felt for many years.”
Drones Provide Data with Unprecedented Precision
To assess the extent of the damage, researchers used fixed-wing UAVs (drones). These provided high-resolution aerial images of the large and often difficult-to-access breeding colonies — a technological advancement that was crucial for the analysis.
Ecologist and co-author Jamie Coleman noted: “We were able to capture three of the world’s largest elephant seal colonies within minutes. Previously, we had to conduct these counts on foot. In wind, snow, and rain we gathered data that are essential for understanding the impact of environmental change on these extraordinary animals.”
The results resemble those from South America, where HPAI has already caused mortality rates of over 70 percent. Unlike in South America, however, the population in South Georgia had been considered protected until now.
Long-Term Monitoring as the Key
For the government of South Georgia and the South Sandwich Islands, the study confirms the need for comprehensive monitoring, which has been in place since 2015.
Sue Gregory of GSGSSI emphasizes: “This study provides a valuable contribution to our ongoing monitoring of top predators and helps us understand regional differences in their response to environmental stressors.”
Long-term research combines ground counts, drone imagery, and satellite data. This toolkit is essential for distinguishing between short-term fluctuations and lasting impacts.
Rosamaria Kubny, PolarJournal