Secrets of the Australian sea lion revealed

By Roy Hunt | April 21, 2015

Researchers brave the aptly named Dangerous Reef to undertake groundbreaking research on the rare – and playful – Australian sea lion.

SOME OF THE islands scattered across South Australia’s Spencer Gulf are verdant, idyllic places. Dangerous Reef is not one of them.

Rising from the ocean 35 km east of Port Lincoln, the island looks from the air like a pristine sliver of sand, but it’s actually a wedge of black metamorphic rock scabbed with sun-bleached guano.

Bleak, desolate and little bigger than a footy field, Dangerous Reef has no permanent fresh water and offers no shelter from the sun, rain or blasting easterly winds.

The guano is treacherous underfoot when wet and dries to a white crust that – when whipped into a gritty powder by the wind – infiltrates everything on the island and adds a peculiar, bitter pungency to every mouthful of food.

Despite its aesthetic shortcomings, this is a place of immense biological significance: the reef supports the largest surviving breeding colony of one of the planet’s rarest marine mammals – the Australian sea lion.

RELATED GALLERY: Australian sea lion

Unravelling the secrets of sea lions 

Seals and sea lions are marine mammals known as pinnipeds; there are 33 species worldwide. All are carnivores that hunt at sea – often for fish and squid – and breed on land, mostly in large, noisy colonies. (Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

I’VE COME HERE near the end of the spring-summer breeding season with marine ecologist Associate Professor Simon Goldsworthy, who has been unravelling the secrets of the Australian sea lion for more than a decade.

Awaiting our arrival is Simon’s colleague and fellow seal expert Dr Brad Page – a giant of a man who, after spending the past couple of tempest-tossed weeks here in a leaky tent with no bathroom facilities, has the wild look of a castaway who’s been isolated from civilisation.

Both researchers have been regular visitors to Dangerous Reef for the past seven years, as they’ve spearheaded a project for the South Australian Research and Development Institute (SARDI) that could help save the sea lion from extinction. Moreover, their unique work with the species is also amassing a wealth of information critical to the future of one of Australia’s most biologically diverse and productive marine regions.

Brad leads us up a gentle slope to a makeshift camp at the foot of the island’s automated lighthouse. Simon and I pitch our tents beside Brad’s on a tiny, nuggetty strip of guano, among boxes of scientific equipment and tinned food.

The Australian sea lion and Australian and New Zealand fur seals are the only species that breed on and around Australia’s mainland and near-shore islands.(Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

I take a few steps beyond an imaginary perimeter for a closer look at our neighbours, but Brad abruptly pulls me up. Two of four female sea lions he’s recently fitted with GPS trackers and miniature ‘Crittercam’ video-recorders – which transform the animals into freelance camera operators and data collectors – are still out at sea. They could haul out any time and Brad won’t risk them being scared off before their precious footage and data have been recovered.

US National Geographic Society (NGS) marine scientist and documentary filmmaker Greg Marshall invented the Crittercam in 1986 to observe behaviour and habitats from the perspectives of wild sharks living off the coast of Belize.

With NGS funding, researchers have used the technology to investigate the lives of more than 40 marine and terrestrial species. The Australian SARDI project is deploying the device on sea lions for the first time, identifying where and how females hunt to support the dietary demands of their growing and dependent pups.

While waiting for the tardy females, Brad takes us to find another sea lion of interest. On the island’s lee shore, a 300 kg male, known technically as Imos 4, reclines pasha-like among his harem of females. He too is a research recruit for Simon and Brad.

Energetic creatures, these sea lions are contributing to the recently developed national Integrated Marine Observing System (IMOS), which employs oceanographic instrumentation on ships, moorings and buoys to map and monitor the marine environment right around Australia.(Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

He’s not, however, carrying a camera on his back but a pocket-dictionary-sized box laden with scientific instruments and satellite antenna. This bull has been transformed into a submersible data-collecting ‘oceanographic observer’, with negligible impact on his health or behaviour.

He represents the other side of SARDI’s sea lion research project, which involves a team of seven males from different colonies gathering data across the Great Australian Bight. Very little is known about life below about 10 m but the use of these deep-diving sea lions is changing that.

“Diving every eight or nine minutes, their capacity to sample their environment far exceeds what humans can do and they’re doing it 24-7,” explains Simon.

These energetic creatures are contributing to the recently developed national Integrated Marine Observing System (IMOS), which employs oceanographic instrumentation on ships, moorings and buoys to map and monitor the marine environment right around Australia.

Australian sea lions and NZ fur seals, along with Antarctic and sub-Antarctic fur seals – which breed on Australian sub-Antarctic islands – belong to the ‘eared’ pinniped family: all have small outwardly visible ears. (Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

Male Australian sea lions have been selected over females for this role because they roam more widely. Unlike any other seal, the species reproduces non-annually and asynchronously: The breeding cycle at Dangerous Reef, for example, is a full six months out of phase with that of Lewis Island just 25 km to the south-west. For males, such as Imos 4, island hopping means ‘staying in the game’ year-round to maximise their reproductive potential.

Simon and I hunker down behind a rock as Brad creeps closer to Imos 4. As he gets within 10 m, there’s a barely audible pop from his tranquilliser gun and the target registers almost no reaction as the dart strikes. It carries a very precisely gauged sedative dose that won’t render the sea lion completely unconscious. If his breathing needs help, an oxygen cylinder is available and an antidote is at hand.

Within minutes our boy looks floppier. Brad prods him gently with a blunt stick to make sure he’s sedated and nods to Simon who then moves swiftly, cutting through dense fur to remove the device glued to the creature’s back. Brad gently takes hold of a flipper, one of a sea lion’s most sensitive parts, and leans close to the big, whiskery face to check his breathing. He’s doing fine – and the muscle and fat he’s piled on since his initial encounter with the research team, five months prior, indicates the backpack isn’t interfering with his feeding.

Sea lions with mounted cameras help researchers 

Australian sea lions have the longest weaning period of any pinniped species. Pups remain with mums for 18 months.(Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

AS SOON AS we arrive back at camp, Simon begins downloading the detailed log of activity from the recovered backpack onto a laptop. The device has been taking regular depth, temperature and salinity readings to document seasonal changes related to one of Australia’s most significant oceanographic phenomena – the Kangaroo Island-Eyre Peninsula upwelling.

These sea lion oceanographers are providing the information needed to map and monitor the development and dynamism of this extraordinary annual marine event, helping to predict the movements of predators and prey in the region with more accuracy than ever before.

This is significant not just for sea lions and other marine wildlife in the Bight, but also for the South Australian sardine fishery, the largest by far of all commercial fisheries operating in Australian waters. It’s annually worth $17.5 million to the Australian economy; most of the 30,000 tonne catch is fed to southern bluefin tuna penned off the South Australian coast.

Ausralian sea lions and NZ fur seals, along with Antarctic and sub-Antarctic fur seals – which breed on Australian sub-Antarctic islands – belong to the ‘eared’ pinniped family: all have small outwardly visible ears. (Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

By late afternoon, Brad’s gear is dry again after the first sunny day for a week and he’s relaxing, jigging for squid from a rocky ledge. He sautés his catch on the camp stove and, still awaiting the return of the camera-toting females, we fall asleep to the grunts and rumbles of sea lions.

The following morning, I’m scanning the water’s edge for the return of the missing females. I marvel as one mum emerges from the water, lifts her head, calls and, more than 30m away, a small pup in a group of several dozen replies almost immediately. Scent confirms the match up as the pair draws close together and the hungry youngster homes in on a teat while mum reclines on a rocky couch.

Swim and snorkel with sea lions at Seal Cove on this island, just a short boat ride from Port Lincoln, SA. The Hopkins colony has become used to human visitors on guided tours. (Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

Australian sea lions dive continually while at sea and must haul out on land to rest. Fur seals, on the other hand, can spend weeks at sea diving for fish. “Whenever they get a bit tired they just come up to the surface, tuck in a flipper and go to sleep, but not these guys,” explains Simon.

When Brad and Simon were here in January, at the height of the breeding season, life in the colony was more frenetic and the researchers had their work cut out avoiding protective mothers as they marked pups to survey their numbers. The only way to work is to have one person marking while the other watches their back.

“I got greedy one day,” says Simon, recalling a momentary lack of focus. A little pup he’d almost tripped over presented a marking opportunity too good to miss. But just as he was making a grab for it, he felt as if he’d been whacked on the back of the leg with a cricket bat. The wound inflicted by the pup’s mum needed 12 stitches.

By the end of my second day on the island, I’ve seen a lot of dozing sea lions but there’s still no sign of the females with cameras.

Camera footage reveal habits of sea lions 

Female sea lions return to breed at the colonies where they were born, are a silver-ash colour and reach about 80kg in weight. (Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

DAWN BREAKS ON my third day in the colony and a flock of Cape Barren geese – common inhabitants of the islands off southern Australia – touches down in the mist at the island’s eastern end. They’re not the only new arrivals. On the rocks beneath the lighthouse – not 10m from our camp and silhouetted against the rising sun – is one of the females we’ve been waiting for.

After spending the past few days fishing at sea she’s finally returned to feed her pup. Brad crawls into position along the ridge above her and she barely twitches as his dart hits home.

Once she’s settled, Simon approaches to cut loose the camera equipment and leaves her with a neat rectangular patch in her fur that will disappear with her next moult. Within minutes, the pup that’s been mewling pitifully throughout the procedure resumes feeding.

Usually researchers identify what seals eat by teasing apart their faeces, looking for squid beaks, crab claws and fish bones. This doesn’t work for Australian sea lions because the prey is so ground up that few identifiable hard parts remain.

The sea lion colony at Poin Labatt Conservation Park, South Australia. (Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

The value of Crittercams is that they answer the same dietary questions – as well as revealing feeding behaviour and foraging habitats – by providing real-life accounts of sea lions hunting. They are, however, expensive research tools and budget constraints have allowed the use of only six on this project during the past two years. But they’ve already produced some revelations.

The video from one female’s camera showed she specialised in preying on a single species, spending her time pursuing octopuses across the seemingly featureless sandy seabed. Another female spent her first day wearing the equipment hunting rock ling in a coastal reef before switching to ‘sit and wait’ predator mode, diving down repeatedly to the same rock where she would perch cat-like watching over a sponge garden. Then she’d pounce on a passing leatherjacket.

Unlike New Zealand fur seals, which also occur in these waters, Australian sea lions are benthic feeders; they forage on the sea floor. The video footage reveals what a demanding lifestyle choice this can be. Any pup growing up around here would need to acquire a range of hunting skills and an intimate knowledge of a feeding territory with very few landmarks.

Simon believes that this explains why the Australian sea lion has the longest weaning period of any seal species: youngsters remain with their mums for 18 months learning this stuff. This is Simon’s ‘family farm’ hypothesis.

Two Australian sea lions play underwater. (Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

The second capture of the day doesn’t go so well. The last Crittercam-bearing female has hauled out among a group that includes at least one large male. Brad can’t get as close as he’d like and his first shot misses. The next appears to hit home, but after several minutes she’s not looking subdued. It was an awkward shot and the tranquilliser dart may not have delivered its full payload; but it’s too risky to attempt hitting her with another.

Simon takes a large net, and positions himself next to Brad as the pair prepares for plan B. The level of agitation among the sea lions moves up a notch and they begin scrambling away. We can’t afford to let our female join the exodus because we might not see her again for another four days.

Simon and Brad are more concerned, however, that if she enters the water while under the tranquilliser’s influence, she could become shark food. Abandoning all pretence at concealment Brad leaps and, like a butterfly collector, drops the net over her shoulders.

Simon then straddles her and, using his body weight to pin her down, removes the camera equipment. By now all the other sea lions have decamped – except for one big bull. We’re messing with one of his girls and he’s not happy; Brad and I keep him distracted and successfully parry his advances in a desperation tango while Simon completes his task.

Sea lions pups curious of divers 

Australian sea lions are often playful and zoom around in the water. (Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

THE NEXT MORNING is my last on Dangerous Reef and I’m able to move about the colony with relative freedom as long as I avoid any sudden moves that might stress the residents. Close to the water’s edge, there are a large number of pups. Most of them are now 3-6 months old and have formed little gangs of 30-40 at a time, banding together to spend their days playing and getting up to mischief.

From a vantage point above a rock pool I watch a group of pups splashing about and playing chase. Occasionally one comes barrelling out of the water into a somersault. They’re honing their aquatic skills and building confidence to meet the challenges of the open ocean.

Back in Adelaide a few days later, Simon and Brad begin the mammoth task of processing the huge amount of data the sea lions have collected over the course of the season. Some of the information will play a part in determining how South Australia’s Department of Environment and Natural Resources should zone 19 new marine parks across the Bight for amenity, limited commercial exploitation or complete protection.

Until now, key habitats and biodiversity indicators in Australia’s oceans have been identified from a human perspective. This, Simon explains, has led to a bias towards habitats with complex structure, such as reefs, because these are known centres of biodiversity. Sea lions, however, perceive things differently.

Sea lion poo contains a high level of bacteria that can metabolise iron and phosporous, important nutriets for phytoplankton, itself a fundamental food for many marine species. (Photo credit: Darren Jew/AUSTRALIAN GEOGRAPHIC)

“They often target areas with very little structure that don’t light up [for us on] our traditional anthropocentric mapping systems but that are often far more productive,” Simon says. What these hotspots lack in biodiversity they often make up for in sheer quantity of available prey.

Simon and Brad predict that, in the long term, a research partnership with Australian sea lions will greatly improve the management of marine eco-systems, not only from the perspectives of threatened species but also from those of commercial fisheries and aquaculture.

As a top predator, the Australian sea lion is also a sentinel of climate change, with the species’ diet and population trends reflecting broader shifts in marine food webs and productivity.

“They are,” Simon explains simply, “providing an enormous wealth of information that will help ensure the better management of Australia’s marine environments in the interests of future generations of both humans and sea lions.”

 

This story was first published in #101 of Australian Geographic.