Photo by Anchor Lee
Bird flu has caused a 47% decline in breeding female southern elephant seals at South Georgia, wiping out around 53,000 individuals at the world’s largest colony of the species, scientists have warned.
The remote sub-Antarctic island is home to 54% of the global breeding population of southern elephant seals, with males of these blubbery giants growing up to two metres long and weighing nearly four tonnes.
New research published in the journal Communications Biology shows that the world’s largest population of southern elephant seals has suffered unprecedented losses following the arrival of highly pathogenic avian influenza H5N1 at the island in late 2023.
Dr Connor Bamford, seal ecologist and lead author from the British Antarctic Survey, said: “The scale of this decline is truly shocking. In typical years, we might see variations of around 3-7% between years, but to see nearly half of the breeding population absent is unprecedented.”
Using cutting-edge aerial survey technology, the research team monitored the three largest breeding colonies on South Georgia – representing 16% of the total female breeding population based on census data from 1995 – comparing breeding female numbers before and after the virus outbreak.
On the same day of the year in 2022 and 2024, scientists used hand-launched drones to take images of the island’s three biggest breeding beaches. Their findings reveal an average reduction of 47% in females, with some colonies experiencing declines of over 60%.
Bamford told AFP: “It paints a pretty stark and harrowing picture.” He added: “I didn’t anticipate it to be this high.”
Many pups also died on the beach after being abandoned by their bird-flu-infected mothers. Scientists at a breeding ground on the Valdes Peninsula along Argentina’s coast have determined that 97% of elephant seal pups died either from being abandoned or contracting bird flu in 2023.
The virus first appeared at South Georgia in September 2023, initially detected in brown skuas before spreading to marine mammals including elephant seals and Antarctic fur seals.
Bamford said: “What makes this particularly concerning is that southern elephant seals are long-lived animals. Even short-term drops in reproductive output or mortality in the breeding population will have long-term impacts on population stability. The ramifications of this outbreak will likely be felt for many years to come.”
In 2024, tourists on cruise ships reported that the explorer Ernest Shackleton’s grave had become inaccessible to visitors due to dead seals blocking the way. However, Bamford said it was likely many dead animals were never seen, having returned to the sea when they were sick to cool down.
“We were aware there was a high level of mortality — way above normal levels — but it wasn’t until we got this before-and-after comparison that we could see how extensive it was,” Bamford said. In the long term, he said, it would have a “dramatic impact on the population”.
The research team considered whether the seals might have simply moved to other locations rather than died. However, the species has strong philopatry, meaning they return to the same beaches year after year.
Bird flu arrived on South Georgia in 2023 during an outbreak that has seen the virus spread across the world like never before, killing millions of birds and infecting many mammals, including several humans.
The research calls for urgent continued monitoring, stating that researchers must return in 2025 and 2026 to see if any of the missing females come back or if the 47% decline represents permanent mortality. The study notes that the long-term impact is yet to be determined and sustained monitoring at major breeding colony beaches is essential to assess the consequences and distinguish short-term fluctuations from enduring population-level impacts.
The research was funded by a Biodiversity Challenge Fund Darwin Plus grant and conducted under permits from the Government of South Georgia and the South Sandwich Islands.