Australian Sea Lion on Kangaroo Island beach

Sea lions of Kangaroo Island under threat

7 October 2020
Meet the vet scientists trying to protect the Australian sea lion
The Australian sea lion is one of the rarest sea lion species in the world, and though they are protected and mostly live in isolated locations, their numbers are falling. Dr Rachael Gray and her team are trying to find out why.

Save our sea lions

Video by Andrew Brettell and Katynna Parry

It isn’t the first time that Australian sea lions have been under threat. Voracious hunting by European settlers in the 19th century dramatically slashed their numbers. While the main target of the hunt was fur seals, the Australian sea lion’s pelt meant it was caught up in the carnage.

The mass-scale hunting stopped only because there were so few seals left it was no longer profitable, allowing fur seal populations to mostly recover. Not so Australian sea lions. They are unique in only breeding every 18 months (12 months for a fur seal), so even in ideal conditions, Australian sea lions are relatively slow to recover.

That said, the current conditions are not ideal. Though Dr Rachael Gray (BVSc ’96, PhD (Vet Science) ’05, GradCertEdStud ’07) is a leading expert on Australian sea lions, even she was surprised to realise how many things are working against the health and even survival of this intelligent, playful, ecologically significant marine species.

A troubling result

Australian sea lion

An Australian sea lion enjoys some time in the sun.

“For a long time, we didn’t look at environmental toxicity. These colonies are so isolated, I thought, ‘there’s nothing there. Everything will be zero’. But when we did study toxicant concentrations, the pups had mercury concentrations similar to those of adult fur seals in the Northern Hemisphere.”

Gray has boundless natural enthusiasm and joy in her work, but the shock is still there as she talks about the mercury result. She has loved ocean mammals since childhood, after seeing them in David Attenborough documentaries.

In high school she wrote to Taronga Zoo looking for marine mammal work experience and spent a blissful time at the zoo sorting fish for the seals and sea lions and cleaning out penguin burrows. “I also love penguins,” she says. “Not so much dolphins, for me. I don’t know why.”

The presence of mercury in the sea lion pups wasn’t the only red flag. Gray and her team have also detected persistent organic pollutants, a type of Escherichia coli (E. coli) bacteria normally associated with humans, and perhaps particularly concerning, antibiotic resistant bacteria.“ This in animals that have never had exposure to antibiotics in the marine ecosystem,” Gray notes.

There is one more, overarching feature of the Australian sea lion population. Every pup has hookworm. Every one of them. It’s more than likely this has always been the case. It’s also likely that hookworm plays a role in the sea lion’s immunological development and intestinal microbiome. Which isn’t to say hookworm is benign.

“It can be deadly,” explains Gray. “It causes a serious infection in the small intestine, so the sea lions lose blood, they lose protein, they lose a lot of weight. They can also cause secondary bacterial infections.”

With sea lion populations declining for reasons not fully understood, the question has to be asked: is hookworm part of the reason for the population decline, or is something else at work?

Dr Rachael Gray and team on Kangaroo Island.

Dr Rachael Gray (centre) and team on Kangaroo Island.

To find the answer, Gray makes regular trips to the sea lion colonies in South Australia with her PhD students. After fourteen years, it’s still a singular experience for her, “It might sound a bit clichéd, but when I walk into a colony, it is always a privilege to be there.”

Gray and her team-work with other institutions including Macquarie University, the University of Adelaide and the Department for the Environment and Water (DEW), South Australia, with funding coming from a number of sources, including through bequests to the School of Veterinary Science, DEW and the Hermon Slade Foundation.

Sea lion research on Kangaroo Island

Australian sea lion in the ocean

Seal Bay Conservation Park is a key sea lion breeding site. The majority of pups here are micro-chipped for individual identification.

One key location is Kangaroo Island which was so devastated by the bushfires at the start of the year. In the immediate aftermath, Gray rushed from Sydney to visit the island and the Seal Bay colony and was enormously relieved to find the latter untouched by the furnace, except for the ash washed ashore.

With the island a tourist centre in normal times, when the team goes there they get to stay in a house with luxurious amenities like running water and electricity. Things are different on the very isolated Olive Island and Dangerous Reef, where they sleep and do their lab work in a tent and cook on a little stove. Gray isn’t complaining.

“The beautiful thing about Dangerous Reef is you lie in your tent and you hear a mum calling and hear about five pups responding,” says Gray. “Then you hear the mum reuniting with her own pup. “Though there are times during the night when you think a massive sea lion is going to run right through your tent.”

This reuniting happens because once the pups reach about 10 days of age, sea lion mothers spend days away foraging in the ocean for food like squid, octopus, cuttlefish, fish, small sharks, rock lobsters, even birds. It’s when the mother’s away that Gray and her team capture and examine sea lion pups, “We’re measuring length, weight and body condition. We also collect a faecal sample and blood sample. Sometimes running is involved.”

That’s running to catch the pups of course, but there are times when a mother sea lion appears unexpectedly and in a bad mood (“We call them Cranky Girls”). Gray has been bitten a couple of times. Another time she turned around to find one of the notoriously bad tempered, 350-kilogram sea lion bull male looking over her shoulder to see what she was doing, “Luckily, he was just curious,” Gray says.

At Seal Bay on Kangaroo Island, during the 2019/20 breeding season, half of the pups caught are treated for hookworm and their health and survival monitored for the next few years, while a control group is monitored but not treated. By comparing the progress of the two groups, Gray hopes to know whether treating hookworm can improve overall animal health and aid the population’s recovery.

Allowing that sea lions have always had hookworm, one possibility is that human pollutants are suppressing sea lion immune systems, allowing hookworms to do more damage than usual. If that’s the case, the plan would be to treat the sea lions for hookworm so they’re not battling threats on both fronts (there is a highly effective hookworm treatment called ivermectin, which can be applied to the skin).

If treating hookworm is not shown to increase pup survival, and thereby improve population numbers, large scale treatment wouldn’t happen. Minimal invasiveness in the lives of the sea lions is a core commandment. Though there are things well beyond Gray’s control.

“Walking through the colonies you see a lot of marine pollution. A lot of plastic. A lot of rope. You see the impact of animals getting entangled,” she said. “And to actually detect the level of organic pollutant in neonatal pups that we’ve seen – that was pretty scary for me.”

The fate of sea lions

To find out more about this story or to help save sea lion populations, please call Kate Parsons on +61 2 8627 8818 or email

Written by George Dodd. Photography by Louise M Cooper. 

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