“TREATMENT OR CONTROL?” Mel Stonnill, research and operations coordinator at Seal Bay Conservation Park, calls out above a blustery onshore wind.

The question is directed to Dr Rachael Gray and her research team, who’ve been bustling around a sea lion pup, collecting samples and data in a finely tuned exercise that takes less than 10 minutes. The answer will mean either a chance at life or a possible death sentence for the little mammal.

It is the 145th pup caught and assessed like this at the Australian sea lion (Neophoca cinerea) colony on Kangaroo Island (KI), 170km from Adelaide, since breeding began here in May this year. A similar process will be repeated at least a dozen times today and through the coming weeks until 180 new pups have been caught, with each recaptured for monitoring up to three times during the season.

This pup’s a female that has been weighed at 11.6kg and measured at a length of 74cm, indicating she’s less than six weeks old, young enough to be included in this landmark trial for the species led by Rachael, a senior lecturer in veterinary pathology at the University of Sydney. Blood has been drawn from a vein in one of the pup’s front flippers and a fur sample clipped from her back, where she’s also been bleached with a distinctive code as a short-term way of recognising her from afar in the colony for the 3–4 months before she moults her soft lanugo fur.

For long-term identification a microchip has been inserted under the skin. If she survives, it will allow her to be followed through to adulthood, when she may produce her own pup at about the age of six years and perhaps several other offspring spaced more than 18 months apart, if she lives to her species’ upper age range.

“Rate: 16,” calls Shannon Taylor, one of Rachael’s PhD students. It’s a breaths-per-minute respiratory rate that indicates the pup’s stress level. Normal is eight, and a worrying level would be up near 30, Shannon explains. “We rarely see that, but if it does rise too high, we release them quickly and monitor them closely from a distance afterwards to ensure they are okay.” The pup’s head has been covered by a loose canvas bag since she was captured, to reduce stress and prevent overstimulating her senses.

“There, there little one,” Mariel Fulham, another of Rachael’s PhD students on the project, says softly as she gently runs her hands over the pup’s back. “Condition is fair,” she calls to Mel, who’s writing everything down. “No lice on belly or back; low numbers on the chest.”

The final and, judging from her yelp, most uncomfortable procedure for this pup has been the extraction of a stool sample from her rectum – unpleasant, but the best way to assess the extent to which she’s infected with a deadly hookworm killing many of these pups. And, despite the wealth of other information this project is yielding about this endangered sea lion, this barely visible hookworm is the fundamental reason everyone is here.

Most pups scurry away quickly after release but this one seemed in no hurry after (L–R) Shannon Taylor, Mariel Fulham, Mel Stonnill and Rachael Gray gathered data about its condition and collected blood, fur and faecal samples for later analysis to complete its health assessment. (Image credit: Quentin Chester)

Rachael has been heading University of Sydney research into the hookworm species Uncinaria sanguinis since she identified its huge impact on pup health and survival

13 years ago. This parasite species is found only in the Australian sea lion and seems likely to have co-evolved with it. The worm infects all Australian sea lion pups and is responsible for up to 40 per cent of pup deaths in the first two months of life.

It’s hard not to be both repulsed and awe-struck by this parasite’s purpose-fit, but fiendish, life strategy. Its eggs can lie dormant for years in beach sand but when its larvae hatch they burrow in through the sea lions’ thick skin. Males are a dead-end host. But in females the worms lurk benignly in body tissues until they’re activated by a physiological trigger just before the sea lions give birth. The worms then move into the mammary glands from where they infect pups as they take their first milk, known as colostrum, which, ironically, is rich in antibodies and designed by nature to be disease-protecting in newborns.

“It takes just 11–14 days for those ingested worms to become adults and start feeding on the intestinal tract of a pup,” Rachael says. “The pups become anaemic and have no energy due to the loss of blood and protein: it causes significant effects on their health and there’s a really high mortality rate.”

Rachael’s team has now completed three trials to treat this worm in pups at the Australian sea lion colony at Dangerous Reef, 35km east of Port Lincoln, in Spencer Gulf. They’ve had huge success making pups hookworm-free and have developed an effective treatment method using a drug called ivermectin, which graziers may recognise as being used for parasites in livestock. In sea lion pups, it’s now being applied topically, for the first time, to a spot on the seal’s fur, just as worm treatments often are for domestic dogs. Because the hookworm only infects sea lions during the first two days after birth, this treatment is needed just once at the right time to save seal pups.

And that’s what has led to this current project, funded by the South Australian Department for Environment and Water (DEW) and the Hermon Slade Foundation, at the Seal Bay colony. Here, the work of Rachael’s team has evolved from a research exercise into a long-term treatment trial for a species in crisis.

With an estimated adult population of 800, Seal Bay is the third largest of the 76 known Australian sea lion breeding colonies, spread along Australia’s southern and south-western coastlines, mostly in South Australia. The species once occurred in Bass Strait and around Tasmania but is now presumed extinct in those areas. Sea lions and seals are classified scientifically as pinnipeds and this endemic Australian species is among the rarest in the group worldwide. With a population of fewer than 12,000 animals, it’s listed as endangered on the IUCN’s Red List of threatened species. It has been nominated to be assigned the same conservation status under Australia’s Environment Protection and Biodiversity Conservation Act 1999.

“Unlike other pinnipeds, these sea lions haven’t recovered from commercial sealing, partly because they don’t have many pups in their lifetime and they have incredibly high pup mortality,” Mel says, explaining the species is thought to have declined by more than 70 per cent during the past 38 years, despite being legally protected. “And we’re also dealing with modern-day issues that every other marine animal faces, from fisheries’

interactions, microplastics and heavy metal pollution to climate change, which is huge for this species because they pup right up against the water.

“So there are lots of modern-day influences affecting the adults now and that’s why we’ve decided to cross that line from monitoring to intervention.”

As far as sea lion colonies go, Seal Bay is a Riviera resort. It’s accessible and reasonably easy for researchers to move around. The population here is well understood because the animals have been microchipped as part of a long-term population monitoring program led by researchers at the South Australian Research and Development Institute in partnership with DEW. A strictly controlled but intensive public education and viewing program at parts of the colony is also run by the latter.

Despite the expectation that this ivermectin trial will help boost Seal Bay’s numbers it’s still considered a research trial and it’s for that reason that pups are either “treatments” or “controls”. Which pup is which is a decision generated randomly by computer before the trial began.

Pup 145 has returned a stool sample full of bloody diarrhoea, indicating it’s already haemorrhaging from hookworm infection. But Rachael’s research has shown that even at such an advanced stage of infection, ivermectin would be a life-saving treatment.

This mother and pup look as if they’re kissing, but this form of contact is about exchanging smells, thought to be important for sea lions to recognise each other. (Image credit: Quentin Chester)

As Rachael flicks through her paperwork to find if pup 145 will be assigned treatment or control status, an inquisitive young juvenile male weighing perhaps 200kg but well short of his ultimate potential bulk, which could be 100kg heavier, approaches within a few metres to investigate the activity. Rachael raises her arms to warn him away, telling him sternly and successfully to “back off”.

As dog-like and endearing as sea lions seem, they can be highly dangerous when they feel threatened. Although Rachael and her team are extremely cautious when moving around the colonies, all have experienced bites and barges at some stage. Rachael was attacked two years ago by a protective female at Dangerous Reef.

“I thought my time was up,” she says, recalling how she lay bleeding and bruised from a wound on her upper back, which still bears the scar.

It’s impossible to approach pups before they’re about two weeks old because the mums don’t leave them alone before then. Each female is also ‘mate guarded’ during that post-birth period by at least one highly testosterone-fuelled male until she comes into oestrus within 7–10 days and is receptive to mating.

This pup’s swollen belly indicates she’s recently fed, but her mum must now be out to sea foraging. Like most pups when their mums are away, she’s moved up and away from the open beach. Some shelter in limestone caves, eroded by the Antarctic winds that buffet KI’s southern coastline, to wait for their mums’ calls when they return. Others hunker down in tunnels of low heathland vegetation, safely away from aggressive and distracted males patrolling the beach for receptive females. These pup havens can surprisingly be several hundred metres away from the water’s edge and located up near-vertical tracts of sand and rock. The mobility that allows sea lions to travel like this on land is one feature that separates them from their torpedo-shaped, shorter-limbed, more water-bound close relatives, the true seals.

What also seems different for the Australian sea lion compared with other pinnipeds is the intimate and long-term relationships, of sometimes longer than 18 months, that develop between mothers and pups. This connection is important to the species because these sea lions remain linked for life to their birth locations, hauling out at them for rest and returning to them to breed. Each colony is associated with particular foraging grounds and the mums need to teach their pups where these are.

It’s these deep social bonds that develop between pups and mothers, and the species’ intelligence and natural inquisitiveness that first drew Rachael to this mammal decades ago.

Finally, Rachael has the verdict for pup 145: “Sorry, guys; she’s a control.” It’s a tough call that means the pup is likely to die from its infection. But what keeps the team motivated is the knowledge that every pup assigned treatment status will almost certainly survive. And that means that this colony is likely to be boosted by many more surviving pups this breeding season than during the last.

This article is featured in Issue 153 of Australian Geographic, which can be purchased here