Worries for sea lions as bird flu spreads to breeding area

By Leah MacLennan

Topic:Avian Influenza

Pages Islands have one of the largest and most stable sea lion colonies. (ABC South East SA: Caroline Horn)

In short:

Mass bird deaths believed to be linked to H5N1 bird flu have been detected on islands that host a large sea lion breeding colony.

While the bird flu strain has not been detected in sea lions in Australia, it has been confirmed in a long‑nosed fur seal in South Australia’s south‑east.

What's next?

The government is considering a vaccination program that was rolled out in seals in Hawaii.

There are concerns the endangered Australian sea lion could be devastated by bird flu, with mass bird deaths found at key seal breeding locations.

While the disease has not been detected in sea lions in Australia so far, federal Environment Minister Julie Collins announced on Saturday that the country had recorded its first case of bird flu in a mammal following testing of a long‑nosed fur seal found in South Australia.

H5 bird flu has affected other pinnipeds in South America and Antarctica.

University of Sydney veterinarian Rachael Gray saw the spread firsthand when she travelled to the sub‑Antarctic region in late 2023.

"It was really saddening," the associate professor said.

"It just really made you think, 'Wow, this has hit here, it's going to be really catastrophic'.

"Not only were there mortalities at the time, but we're now seeing papers coming out talking about reduced numbers coming back to breed in subsequent years, so it really was very sobering and very upsetting to see."

South Australia is home to hundreds of sea lions. (Supplied: SA government)

Dr Gray is an expert in the Australian sea lion, which is recorded as endangered on international threatened species lists.

Its entire population is estimated as fewer than 10,000, with 85 per cent in South Australia and the remaining 15 per cent in Western Australia.

A bird's unusual and disturbing behaviour catches the eye of passers‑by. On the ground it flaps its wings, turns in circles and then somersaults.

One of the largest breeding colonies is located on the tiny and remote Pages Islands between Kangaroo Island and the South Australian mainland.

The Pages were the location of two of three mass deaths revealed by the South Australian government on Thursday, where about 1,000 birds, mostly greater crested terns, were found dead.

Authorities are still awaiting testing results to confirm if the birds contracted H5N1.

The development prompted unease in Dr Gray.

"[It's] very concerning when it's at Australian sea lion colonies," she said.

"It's also been detected at Seal Bay as well, a really iconic South Australian destination. It's very frightening."

The SA government has been conducting aerial surveillance of animals including sea lions for bird flu since June. (Supplied: SA government)

The Australian sea lion was already facing difficulty, with an increase in pup deaths during the 2025 breeding season.

Government observers counted 84 dead pups across two visits to The Pages, a mortality rate of more than 34 per cent, compared with the recent average of 5 per cent.

While the exact cause is unclear, the deaths were largely attributed to the algal bloom, with a lack of food causing stress for mothers and their pups.

But Dr Gray said there had been time to build some resilience in populations.

Vaccination being explored

In response to the pup deaths in 2025, state and federal governments committed $1.4 million to continue a program of worming pups and erecting shelters at colony sites to protect them from the elements and other adult sea lions.

Rachael Gray and her team have been worming sea lion pups for their protection. (ABC News: Che Chorley)

Dr Gray is involved in the worming program, regularly travelling to Kangaroo Island to treat sea lion pups for hookworm, a parasite that causes serious health problems in the species.

"It's to basically give them a chance to grow better and to have better, I guess, what we call 'fitness' when they get older," she said.

"So that when another threat like avian influenza or another pathogen comes into the picture, they're better placed to actually deal with that pathogen or that infection."

SA Environment Minister Emily Bourke said the government was concerned about the sea lion population, which was one of the reasons it had invested heavily in a bird flu monitoring and surveillance program.

She said the government was also looking into a vaccination program of seals in Hawaii.

"We have expressed our willingness to the federal government to further explore that opportunity," she said.

"But also keeping in mind that this isn't an approved vaccination, and that's why we need to consider the options that are available to us."

Emily Bourke has raised the possibility of vaccination. (ABC News: Lincoln Rothall)

Unlike other pinniped species, the Australian sea lion population struggled to recover from when it was hunted for fur.

Its continued low numbers have been blamed on its unique breeding cycle, in which mothers do not wean pups until 18 months.

Dr Gray is hopeful that feature may help them survive bird flu.

"The novel thing about the Australian sea lion is that unlike other pinnipeds, pups aren't born at a site over a really distinct period of time," she said.

"They're born over an extended period of time, so perhaps if a virus hits at a time when there's not a lot of pups there, then maybe the impact will be lessened, but it's really too early to tell."

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