A year later and researchers have announced that the virus might have spread further still, reaching the Australian sub-Antarctic islands of Heard and McDonald Islands, less than 500km (311 miles) away from Kerguelen. There they found several dead elephant seals, including pups, which have not yet been tested for the flu. To date, Australia is the only continent that remains free from the highly contagious bird flu.

Researchers are now racing to assess how much worse the impact of these creatures could still get. Boulinier’s team was the first to witness the impact of the bird flu in the Indian Ocean. Last season, wearing hazmat suits, they collected blood from live animals and brain tissue samples from the carcasses of several species. They hope to better understand how the virus is spreading and if the animals are developing any immunity against it.

So far, blood sample analysis has been mostly negative for antibodies among elephant seals in this region, suggesting that a large portion of the population has not yet been exposed to the virus or developed immunity. “That raises concerns,” says Boulinier, who is leaving for the islands to continue monitoring in a few weeks. “If there is another outbreak this year, it may also be devastating.” Many of the seal species found in Antarctica and Sub-Antarctic regions are endemic and can only be found in these places, making mass die offs an even greater threat.

A ‘cascade’ of harm

What could this spread mean for the rest of life in the oceans? Elephant seals are top predators in the food chain, and a decline in their population can lead to cascading effects impacting the whole ecosystem, according to researchers, causing an increase in some fish species and a decrease in others, for example. 

Elephant seals are also especially important as an “ocean fertiliser”, says Uhart. They are incredible divers, able to hold their breath for up to two hours and go as deep as 2.1km (7,000ft) in their pursuit of fish. In this process, they spread nutrients from their faeces in different layers of the water, feeding other creatures.