More than 13,000 southern elephant seal pups died from H5N1 bird flu on the Heard and McDonald Islands [1].
This event marks the first time this specific pathogenic strain of avian influenza has been detected causing mortality in seals. The scale of the loss threatens the stability of the local seal population in one of the world's most isolated environments.
Australian scientists discovered the devastation during a research expedition that arrived in October 2025 [5]. The findings were reported this month. The affected area consists of the Heard Island and McDonald Islands, a sub-Antarctic Australian external territory located approximately 4,000 km south of the mainland [4].
The virus caused an unprecedented collapse among the young seals. While some reports indicate more than 75% of baby seals were killed [2], other data suggests nearly 80% of the southern elephant seal pup population was wiped out [3]. The high mortality rate highlights the vulnerability of marine mammals to avian viruses.
Researchers identified the virus strain as H5N1 [6]. This strain is known for its high pathogenicity in birds, but its jump to a significant number of marine mammals on these remote islands suggests a shift in how the virus spreads across different species.
The islands serve as critical breeding grounds for southern elephant seals. The loss of thousands of pups in a single season creates a demographic gap that could affect the population's recovery for years to come, especially given the remote nature of the territory which makes monitoring difficult.
Scientists continue to study the samples collected during the October 2025 expedition to determine how the virus was introduced to the islands and whether other wildlife species are at risk.
“More than 13,000 southern elephant seal pups died from H5N1 bird flu”
The jump of H5N1 from avian populations to marine mammals on such a massive scale indicates an expanding host range for the virus. This event suggests that sub-Antarctic ecosystems are no longer isolated from global pandemics, posing a long-term threat to biodiversity and the survival of endangered or vulnerable marine species.
