Seal numbers on Victorian island plummet as pollution affects pups

Deen Maar Island fur seal population plummets as pollution affects pups Sun 9 Aug 2026 at 6:31am In short: Australian fur seals on the south-west Victorian island Deen Maar are reportedly suffering from widespread hair loss that has been linked to pollution. The colony's population has declined more than 40 per cent in the past nine years. What's next? There are concerns the hair loss, attributed to alopecia, could make the seals more vulnerable to the H5N1 strain of bird flu. A remote island off Victoria's south-west coast, Deen Maar, was once home to Australia's largest fur seal colony. The small rocky island, also known as Lady Julia Percy Island, sits in waters near Port Fairy, 8 kilometres offshore from the tiny town of Yambuk. It is difficult to reach by boat and illegal to visit without a permit. Twenty years ago, the population was thriving, with an estimated minimum of 2,000 seal pups born on the island each summer. Now the population is shrinking, with just 700 pups spotted during a February count. Experts believe hair loss among the seals, which has been linked to pollution, is behind the declining numbers. The Eastern Maar Aboriginal Corporation and Gunditj Mirring Traditional Owners Aboriginal Corporation are the local custodians of the waters around Deen Maar. Eastern Maar's sea country coordinator, Dave Williams, said he became worried about the local seal colony after spotting large patches of fur loss. "When their hair falls out, they can't keep warm, and if they can't spend much time in the water, then they can't feed for as long," Mr Williams said. Australian fur seals have a coarse outer layer of fur that traps air and keeps them waterproof. When that layer of fur is broken, water can soak the woolly underfur, causing the seals to lose the ability to thermoregulate, which can lead to poor health and even death. "When you can't get enough food, it affects everything — it's a domino effect,"Mr Williams said. "The pups who are depending on the mother suffer; they end up being smaller pups, and if they haven't got enough fat to keep them warm, they may not make [it through] that first year." He said a recent head count on the island revealed seal pup numbers had reduced by more than 40 per cent since the last count in 2017, and more than 65 per cent since 2007. "We've seen a surprising number of individuals with alopecia," Mr Williams said. He said he feared alopecia would weaken the seals' chances of survival from the deadly H5N1 strain of bird flu, which was recently detected in nearby Portland, about 25 kilometres from Deen Maar. Pollution on the western Victorian coast Marine researcher at Phillip Island Nature Parks Rebecca McIntosh said widespread alopecia had never been seen in an Australian fur seal colony. "You only see it at Deen Maar Island and [nearby] Cape Bridgewater, [but it's] mostly at Deen Maar," Dr McIntosh said. "At Seal Rocks on Phillip Island, there'd be 8,000 animals there. You might see one with alopecia like once a year. "It's definitely an issue for the west." Penguins on Deen Maar were found with high levels of aluminium and titanium in their feathers. Dr McIntosh said she believed this was a sign Deen Maar's proximity to industrial areas in Portland could be a significant source of pollution, and she hoped to investigate in future research. Threatened by pollution Research published in the Journal of Mammalogy found fur seals with alopecia had higher levels of heavy metals and persistent organic pollutants, which could indicate they were foraging in areas where pollution was greater. Eastern Maar Aboriginal Corporation sea country manager Mandy Watson said it was difficult to help the colony without knowing where the pollutants came from. "Alopecia has been linked to persistent organic pollutants in the marine environment, and we need to find out, if we can, exactly what the source of that could be," Ms Watson said. "What we don't know is why this particular colony has been hit harder by alopecia than others. "That would suggest that there is something in the local marine environment." E. coli from human waste and PFAS have been detected in seals across multiple colonies in the Bass Strait. A research collaboration between the sea country teams and Phillip Island Nature Parks aims to track where this pollution originates. Ms Watson said if the seals at Deen Maar were suffering from pollution, the island's penguins, birds and surrounding waters could be struggling as well. "You'd think if it's affecting the seals — they're the top predators, at the top of the ecosystem — it would definitely be having effects all the way up the food chain," she said. Threat to species survival Australian fur seals were nearly hunted to extinction in the 19th century. Dr McIntosh said this caused a lasting loss in the species' genetic diversity, and if the colony on Deen Maar died out, it could threaten the long-term survival of the entire species. "Deen Maar seems to have quite distinct genetics from the other sites, and it might make it even more important that we try to protect those seals," she said. "When you're faced with challenges like climate change, you need to have as much genetic diversity as possible, so they've got the best chance of adapting to those changes. "We think that Deen Maar might've been the source population for most of the modern fur seals after they were overharvested by the commercial sealing industry in the 1800s."