Tiny, lost and constipated: what a baby turtle told Australian scientists about warming seas | Reptiles

WWhen Bulwal Bilima (BB for short) first arrived at Taronga Zoo in Sydney, Australia, she, or perhaps he, was lethargic, severely constipated and dehydrated. Named “strong turtle” in the Dhurga aboriginal language of the Yuin people on the land on which it was found, the small 110g loggerhead turtle, no bigger than a bar of soap, had to fight.

The baby turtle was found stranded in Booderee National Park, New South Wales, last April, much further south than usual hatching areas. After days of feeding on squid, sardines and marine vitamins, BB, whose sex can only be determined when mature, has resurrected.

During the winter, BB stayed in heated rehabilitation pools to thermoregulate while the offshore waters remained too cold. Last month it was finally fitted with a satellite tracking system and released from Lord Howe Island, about 700km northeast of Sydney.

For conservationists, the rescue was about more than saving a turtle’s life. It was a fresh warning that warming seas are forcing species to move into new territories.

The East Australian Current is strengthening and pushing warmer waters further south. Marine species once largely confined to Queensland, including the endangered loggerhead turtles, are now appearing much further south in New South Wales, in places where they had rarely been seen before.

For Taronga scientists, these changes require a new strategy. Using satellite trackers and new marking techniques, they follow the movements of rehabilitated and wild turtles in real time. The objective is to anticipate the next movements of turtles and new migration corridors which may require protection in the years to come.

Loggerheads, one of the world’s seven species of sea turtles, are found all over the world. They can live up to 80 years, reach 1.2 meters in length and weigh up to 180kg (28 stone). Recognizable by their stubby heads, reddish-brown shells and powerful jaws, they have complex migratory patterns, often spending decades on the high seas before returning to their native beaches to nest.

Phoebe Meagher, a conservation officer who works on the Taronga turtle tagging project, says their move south raises urgent conservation concerns.

“We have a lot of turtles nesting in New South Wales, which was never the case before, and so the question is: what does this mean for the conservation of the species? It’s not about where turtles live now, it’s about where a turtle will live in the future.”

The basic data needed to help scientists solve this problem is scarce. “Nothing is known about sea turtles in New South Wales. In fact, there is so little information that Commonwealth maps of biologically important areas for marine species did not contain any data points for sea turtles in New South Wales,” says Meagher, referring to regions designated for marine protection.

The Taronga tagging project aims to fill this gap and inform wildlife management of future habitat protection strategies and areas.

Often called sentinels of climate change, turtles are very sensitive to environmental changes. The temperature of the sand determines the sex of the hatchlings: cooler sand produces males, warmer sand, females. As turtles move south, differences between ocean and sand temperatures could distort sex ratios or reduce survival.

Intensifying currents can also alter habitat quality, increase the risk of disease, and bring turtles closer to humans, increasing uncertainty for already threatened species.

Kimberly Vinette Herrin, a veterinarian in Taronga who rehabilitated and released BB, witnessed these consequences firsthand. “We’re seeing a lot more impact from humans… [such as] fishing lines, boat collisions, plastic ingestion,” she says.

Entanglement can lead to amputated fins and embedded hooks. Changing migratory patterns can also expose turtles to unknown pathogens.

As BB regained strength, Herrin’s team monitored sea temperatures and feeding conditions around Lord Howe Island, an isolated UNESCO-listed volcanic remnant close to the East Australian Current.

“We wanted to be careful not to use BB in very cold temperatures that might not be suitable,” says Herrin. “We always want it to be a little over 20°C, so they [turtles] have the best chance of success.

In mid-February, BB had a final health check-up. A small satellite tracker was attached to its hull with epoxy and fiberglass, and Herrin flew with the team to the island to be released into the current.

“It’s like your child because you’ve had it for a year. We can’t keep it in captivity. It’s the right thing to do. But you really hope it’s not just a piece for something,” she says.

For two days after release, BB’s tracker pinged regularly. Then it got quiet.

“I was horrified, absolutely horrified,” Herrin says. “But the next day, there’s a trace. It went really far north, and then it started coming back. So I think it’s starting to find and get into the current.”

BB is one of 21 turtles tracked by Taronga conservationists along the NSW coast – including 16 green turtles, three loggerhead turtles and two hawksbill turtles. Unlike the shallows of Queensland where researchers can often mark turtles standing, marking turtles moving south in the deeper, low-visibility waters of New South Wales has required new methods.

“If we find a turtle resting, they tend to hide under ledges. And if we can catch the turtles resting, it’s actually a much less stressful capture because they’re half asleep. Developing this method has been one of our biggest victories,” says Meagher.

For larger loggerheads, the researchers used mesh nets attached to a boat, sliding them under the turtles to gently lift them aboard.

For Herrin, who has rehabilitated and released numerous turtles, the most powerful moments of the process remain the simplest.

“When they swim away and don’t look back, we know we did well, so that’s the best thank you we can get,” she says.