An H5 strain of avian influenza has killed thousands of southern elephant seal pups on Heard Island in the Southern Ocean [1, 2].
This mass mortality event highlights the increasing ability of bird flu to jump between species and devastate wildlife in remote, fragile ecosystems. The scale of the loss threatens the immediate stability of the local southern elephant seal population.
Researchers first detected the virus on the remote Australian sub-Antarctic territory in late 2025 [1, 5]. The virus spread rapidly among the densely packed pups, leading to a catastrophic outbreak [1, 5].
Reports on the total number of deaths vary. Some data indicate approximately 13,000 seal pups died [1], while other reports state the number was more than 13,000 [3]. A higher estimate suggests that tens of thousands of pups were killed [4].
The proportion of the pup population wiped out is also subject to varying reports. Some data show that more than three-quarters, roughly 75%, of the pups died [1]. Other reporting places the loss at nearly 80% [6].
Heard Island remains a critical breeding ground for the species. The high density of the colony likely facilitated the rapid transmission of the H5 strain among the young seals [1, 5]. Scientists continue to monitor the impact of the virus on the remaining population and other wildlife in the region [5].
“An H5 strain of avian influenza has killed thousands of southern elephant seal pups on Heard Island.”
The outbreak on Heard Island demonstrates that H5 avian influenza is no longer confined to avian populations but is actively circulating among marine mammals in the Southern Ocean. The high mortality rate among pups, ranging from 75% to 80%, suggests that young seals are particularly vulnerable to this strain. This event underscores a growing concern for global biodiversity, as remote territories that once served as natural refuges are now susceptible to highly contagious zoonotic diseases.
