How a feisty turtle named Seven Hook is revealing the secrets of Sydney’s underwater nurseries

The turtle named Seven Hook is tough and feisty. It was true when she lay riddled with barbed metal and fishing wire on an operating table, surrounded by vets who presumed she’d die.

And it’s true two months later, when the scent of the sea has animated her entire 50-kilogram body and she flaps and bobs her head on board the police boat jetting her out between the heads of Sydney Harbour.

Seven Hook, a green sea turtle, was the sixth turtle brought into Taronga Zoo Wildlife Hospital this year and the 44th in their turtle tracking program, which after a decade has just collected enough data to start analysing the trajectories of these global travellers. The early findings suggest that turtles’ lives are far more intimately entwined with ours than researchers expected.

A GPS tracker is affixed to the shell of a green turtle named Seven Hook by Taronga Zoo’s Libby Hall.Credit: Brook Mitchell

Seven Hook was found languishing offshore from Lake Macquarie, south of Newcastle, and named for the number of hooks lodged in her guts. It’s the most hooks vet Dr Larry Vogelnest has seen in a single turtle, although it was only last month he operated on a young female who’d be named Five Hook.

“Fish hooks in themselves are not a disaster, necessarily. It’s the line that’s the worst thing,” Vogelnest says.

He’s just emerged from the hospital’s operating room, following another staff member who slipped out holding a set of glass slides smeared with a bloody substance – koala bone marrow. “Are you guys right with the guinea pig?” he calls over his shoulder to affirmative nods. We walk past reception, where a rose-crowned fruit dove in a cat crate awaits attention.

He’s nonchalant when asked about the variety of anatomies he’s called to operate on.

“That’s what we do as zoo vets,” he says. “We work on frogs and elephants on the same day.”

Vogelnest’s prognosis for Seven Hook was grim.

“Surgery in turtles is very challenging. They’re encased in this enormous shell and there’s only a couple of little windows that you can actually get in there,” he says.

“I made the incision, went into the body cavity and pulled out the intestines. I could feel the hooks. It’s very hard to get a large amount of their intestines out, I had to do it in sections, tugging and pulling.

“I had very poor expectations about this animal, that it was going to survive. It was five hours of surgery.”

Fishing line bunches up in a turtle’s digestive system, concertinaing the intestines and slicing through the soft tissue. And then there’s the glut of plastic bags, netting, balloons and wet wipes.

“Often we’ve found that you open them up, and it’s just a disaster, and you can’t fix it, and we just euthanize them.” Vogelnest says. “So we’re pretty thrilled with this outcome.”

Seven Hook, who’s approaching the size of a coffee table with flippers, is likely a 40-year-old female close to breeding age. But most of the sick turtles coming into Taronga are young (closer to the size of dinner plates and serving platters).

The movements of these younger turtles in particular have long been an international mystery; precious little is known about where they go between that mad scramble towards the shoreline as hatchlings and their return to that same beach as adults to breed and lay eggs.

Ten years ago, the zoo’s Dr Kimberly Vinette Herrin and Libby Hall began tracking the turtles that survived surgery to see if they could shed light on the mystery.

“There’s this huge gap in knowledge,” says Hall. “There’s no information on young turtles, in NSW especially. They’re called ‘the lost years’.”

She’s looking at a map on her computer screen flecked with green and red dots depicting turtle locations. Beside four tracker IDs, a green icon pulses, signifying the tracker is still live and pinging twice a day off the Argos satellite. Now Hall and Herrin have gathered more than 40 datasets since their first tracked turtle in 2013, they can start to unpick patterns.

It’s early days, but something unexpected has already emerged: the young sea turtle is an urban creature.

“What some of the Indigenous elders in the area had said is, ‘oh, there are turtles all through the waterways around the Sydney area’,” Hall says. “We listened to that. And they, of course, were right.”

Some young turtles escorted out beyond the heads shot back towards the Harbour Bridge and travelled deep into urban Sydney waterways. Others frequented Pittwater, swam way up the Hawkesbury River and glided past Gosford. Another, named Shelby, swam straight down the coast to the busy Shellharbour marina she was rescued from.

“Everyone thinks they go off and out into the beautiful blue ocean. But in fact, they’re coming right up against the shore, coming into where all the people are,” Hall says.

“As Sydneysiders, we’re living in a beautiful environment, and we know that we’ve got amazing wildlife. But do Sydneysiders recognise that they’ve got marine turtles as neighbours?”

The working theory is that the young turtles head up urban waterways to feast on moon jellies (“We call them breast implants,” says Hall) before their gut develops to eat seagrass and they’re big enough to survive the open sea.

It means they could be far more frequent in busy, hazardous urban waterways than once thought.

Seven Hook’s hospital mate, an 80-kilogram female named Anna, was rescued near Nelson Bay, which the tracking data has shown is a sea turtle haven.

“It’s known to have a large population of marine turtles and it is a very dangerous place too,” Hall says. “There’s lots of fishing, traps, netting, debris in the water. It’s a very popular space, especially in the summertime. Boat and jet ski strikes are not uncommon.”

Hall’s tracking data shows many young turtles hug the coast and enter urban waterways, possibly in search of moon jellies.Credit: Brook Mitchell

Anna is missing a flipper, potentially constricted and severed by tight wire or netting, and has a deep grey gash in her head likely inflicted by a jet ski. She was a victim of “floating syndrome”, when turtles bloated by line and plastic can’t dive and are forced to float on the surface where they’re vulnerable to strikes. Post-treatment, Anna is settled comfortably on the bottom of her hospital pond.

“This is my box of death,” Hall says darkly, opening a tub filled with yellow-lidded jars of wrinkled balloons, fishing wire, sinkers as long as fingers, and frayed black “biodegradable” bags. All have been pulled from dead turtles and seabirds.

“Marine turtles are such important animals. I mean, they’re basically living dinosaurs,” she continues, balancing the jars of rubbish on her knees. “A hundred million years they’ve been roaming the oceans. They’re significant animals to indigenous people all around the world. And unfortunately, in 200 years, we’ve changed the environment, the oceans to such an extent that they’re endangered worldwide. Every species.”

Climate change is also a problem for turtles because temperature dictates the sex of their hatchlings – one study found a temperature increase of just 1 degree meant 80 per cent of green sea turtle hatchlings were female. Urban beaches closer to Sydney could become important nesting grounds for sea turtles, Hall says, as climate change warms beaches further north.

Data is the lifeblood of any conservation effort and Hall hopes their findings, once published, could help establish more marine parks where the turtles gather.

“That’s something we need desperately in the Sydney area. We have such abundant marine life and we only have a couple of sanctuaries. This sort of data will help with all of those things – you can’t do conservation without the data.”

After surgery, Seven Hook struggled to recover for a few days and rejected food. But she quickly began to rally. Her daily check-up X-rays became an ordeal as her strength and fight returned. Soon she was well enough for Hall to affix a tracker to her, in front of a boat strike injury that cracked part of her shell into jagged white shapes that interrupt the green marbling of her carapace; yet another trauma she withstood.

Seven Hook was released alongside Anna on the last day of autumn, before the water becomes too cold. Hall kept a calming hand on Seven Hook’s head on the way out to sea; as soon as turtles are escorted out between the heads it’s like they can sense the open ocean, and they thrash with energy.

Once freed, Anna circled the boat a few times before moving off into the deep.

True to form, Seven Hook wasted no time.

“Seven Hook just shot off into the blue, so quickly,” Hall laughs. “I’m just going home so happy because they’re home, out in the ocean.”

In coming months, the green icon flashing beside Seven Hook’s ID will pulse a final time as her tracker runs flat.

She’ll leave the people who saved her with an arrangement of dots scattered across a map that spell out her journey from Sydney, and the seven hooks they cut from her, kept in a jar with the yellow lid screwed tight.

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