When Bulwal Bilima (BB for short) first arrived at Taronga Zoo in Sydney, Australia, she, or possibly he, was lethargic, badly constipated and dehydrated. Named “strong turtle” in the Aboriginal Dhurga language of the Yuin people on whose land it was found, the tiny 110g loggerhead hatchling, no bigger than a bar of soap, had a fight on its hands.
The baby turtle was found stranded in New South Wales’s Booderee national park last April, much further south than the usual hatching grounds. After days of feeding on squid, sardines and marine vitamins, BB, whose sex cannot be determined until it is fully mature, revived.
Through winter, BB remained in heated rehabilitation pools to thermoregulate while offshore waters remained too cold. Then last month, it was finally fitted with a satellite tracker and released from Lord Howe Island, about 700km north-east of Sydney.
For conservationists, the rescue was about more than saving the life of one turtle. It was a fresh warning that warming seas are forcing species into new territories.
The East Australian Current is strengthening and pushing warmer waters further south. Marine species once largely confined to Queensland, including endangered loggerhead turtles, are now turning up much further south in New South Wales – in places they have rarely been recorded before.
BB is released from rehabilitation – video
For Taronga’s scientists, those shifts demand a new strategy. Using satellite trackers and new tagging techniques, they are following both rehabilitated and wild turtles’ movements in real time. The goal is to anticipate where turtles will move next and which emerging migration corridors may need protection in the years to come.
Loggerheads, one of the world’s seven sea turtle species, are found worldwide. They can live up to 80 years, reach 1.2 metres in length and weigh up to 180kg (28 stone). Recognisable by their blocky heads, reddish-brown shells and powerful jaws, they have complex migratory patterns, often spending decades in the open ocean before returning to their natal beaches to nest.
Phoebe Meagher, a conservation officer who works on Taronga’s turtle tagging project, says their southward shift raises urgent conservation concerns.
“We’ve got lots of turtles nesting down in New South Wales, which they never used to do, and so the question is, what does this mean for the conservation of the species? It’s not about where the turtles live now, it’s about where a turtle is going to live in the future.”
Taronga conservation biologist Dr Jo Day and conservation officer Dr Phoebe Meagher release a tagged green turtle into the sea.
The baseline data needed to help scientists work this out is scarce. “Nothing is known about marine turtles in New South Wales. In fact, there is so little information that the Commonwealth maps of biologically important areas for marine species had zero data points for marine turtles in New South Wales,” Meagher says, referring to regions designated for marine protection.
Taronga’s tagging project aims to close that gap and inform wildlife management of future habitat protections strategies and areas.
double quotation markWe can’t keep it in captivity. It is the right thing to do. But you really hope that it’s not just a morsel for somethingKimberly Vinette Herrin, Taronga Zoo
Often called sentinels of climate change, turtles are highly sensitive to environmental shifts. Sand temperature determines hatchling sex: cooler sand produces males, hotter sand, females. As turtles move south, mismatches between ocean and sand temperatures could skew sex ratios or reduce survival.
Intensifying currents may also alter habitat suitability, increase disease risk and push turtles closer to people – compounding uncertainty for already threatened species.
Kimberly Vinette Herrin, a veterinary officer at Taronga who rehabilitated and released BB, has seen those consequences first-hand. “We see a lot more impact from humans … [such as] fishing lines, boat strikes, plastic ingestion,” she says.
Entanglement can lead to amputated flippers and embedded hooks. Changing migratory patterns can also expose turtles to unfamiliar pathogens.
BB is given a final health check by Taronga wildlife hospital vet Kimberly Vinette Herrin before being released.
As BB regained strength, Herrin’s team monitored sea temperatures and foraging conditions around Lord Howe Island, a remote Unesco-listed volcanic remnant close to the East Australian Current.
“We wanted to be careful about putting BB out in really cold temperatures that might not be so suitable,” says Herrin. “We always want it to be a little bit over 20C, so they [turtles] have the best chance of doing well.”
In mid-February, BB passed a final health check. A small satellite tracker was secured to its shell with epoxy and fibreglass, and Herrin flew with the team to the island for the release into the current.
BB is rehabilitated in heated pools – video
“It’s like your child because you had it for a year. We can’t keep it in captivity. It is the right thing to do. But you really hope that it’s not just a morsel for something,” she says.
For two days after release, BB’s tracker pinged regularly. Then it went silent.
“I was horrified, absolutely horrified,” Herrin says. “But then the next day, there’s a track. It had gone way up north and then it started coming back around. So I think it’s starting to find and get into the current.”
BB is one of about 21 turtles tracked by Taronga conservationists along the New South Wales coast – including 16 green turtles, three loggerheads and two hawksbills. Unlike the shallows of Queensland where researchers can often tag turtles while standing, tagging the southward-moving turtles in New South Wales’s deeper and low-visibility waters has required new methods.
The tracks of loggerhead turtles overlaid on top of ocean currents off the coast of New South Wales.
“If we find a turtle resting, they tend to tuck themselves under ledges. And if we can catch the resting turtles, it’s actually a much less stressful capture because they’re half asleep. Developing that method has been one of our biggest wins,” Meagher says.
For larger loggerheads, researchers have used mesh nets secured to a boat, sliding them beneath turtles to lift them gently on board.
For Herrin, who has rehabilitated and released many turtles, the most powerful moments in the process remain the simplest.
“When they swim away and they don’t look back, we know we’ve done OK, so that’s the best thanks that we can get,” she says.
