A flatback (Natator depressus) turtle hatchling crawls towards the water's edge at Eco Beach, WA. (Carolyn Barry) Image Credit: Video produced and edited by Carolyn Barry

Tracking turtle nests at Eco Beach, WA

  • BY Carolyn Barry |
  • March 15, 2012

Flatback are the only sea turtle species endemic to Australian waters, but much remains uknown about them.

IT'S ALREADY ABOUT 36ºC at 8am and we're all sweating up a storm, despite being just 20m from the sea. In the stillness, we listen intently. All we can hear, aside from the gently lapping waves, is the long swish...swish of a modified fishing rod plunging slowly, deliberately into the sand.

"No, I don't think anything is here," concludes Glenn McFarlane, a passionate turtle researcher with Conservation Volunteers.

"Here" is a potential turtle nesting site on the remote and impossibly beautiful Eco Beach, about a 1.5hr drive south of Broome, Western Australia. The project, led by Glenn, is slowly developing a picture of the status of the flatback turtle (Natator depressus) - Australia's only endemic sea turtle species.

Much is unknown about the flatback - named for its smooth carapace - as its range is so small. Unlike the six other sea turtle species that roam the world's oceans, this one curiously stays pretty local - in the tropical waters between the northern Australia and New Guinea.

While the species is classified as 'Rare or likely to become Extinct' under the Wildlife Conservation Act in Western Australia and 'Vulnerable' nationally, the IUCN records them as 'Data Deficient'. However, it's likely the flatback - which lives to more than 50 years and reaches sexual maturity after 20 years - is under threat and its conservation should be a priority, Glenn says. "Once the species becomes extinct here, it's extinct everywhere," he says.

Though their feeding and breeding grounds are currently not formally protected, the federal government is considering a draft proposal for a marine reserve which covers some this habitat. However, says Jenita Enevoldsen, from The Wilderness Society, "In order to truly protect flatback sea turtle habitats, large networks of marine sanctuaries are needed along the continental shelf off the Ningaloo and Kimberley coasts."

Flatback turtles: mysterious life cycle

Flatbacks lay about 50 eggs in early summer - typically around November-December - returning, remarkably, to the exact beach at which they hatched. After about a 45 to 55-day incubation, the hatchlings dig themselves out, en masse, instinctively heading straight to the sea.

Not all of them make it, though, and not all of them even hatch. Many factors can come into play - poor nest conditions; attack from bacteria, fungus, ants or crabs; or predation by foxes, feral cats, dingoes and birds.

That's where we come in. It's mid-February - the wet season up here - and most of the hatchlings are long gone. Only a few late-season nests remain incubating. Our job is to locate the hatched nests and dig them up, noting how many eggs are left, what stage of development they're in and why they may not have hatched.

A previous research group has marked the spot where they surmised a turtle nest should be (based on sighting a nesting turtle, or tracks of one) and it's our job to exhume it.

The task sounds easier than it is. While the marking system used by the researchers gives a good indication of where a nest might be, finding the exact spot is tricky. The nest hole is no bigger than about 20cm in diameter and unless there are tracks right up to the spot (this is rare), it's like finding the proverbial needle. 

Unusual methods to track turtle nests

Over the past nine years researching turtles, Glenn has proudly exhumed 38,322 eggs, using strategies he learnt from those who do it best: poachers.

"If you use the skills of a poacher, you can locate and then preserve the nest," he says. "I use those skills to teach our staff. It's instinct and feel."

Those skills include using his makeshift truncated fishing rod to 'feel' the sand at the upper entrance of a turtle nest.

By slowing plunging the rod into the sand, he can feel the resistance of increasingly deeper, heavy-packed sand. When the rod is inserted into the entrance of the nest (the shortened rod is not long enough to penetrate anywhere near the actual egg chamber), the loosened sand below the surface gives a different resistance and the sound and feel of the rod changes.

After declaring one nest a 'false crawl' (where no eggs are deposited), we move to the next on the list. There's supposed to be another site nearby but it doesn't look promising - there are rocks all around and it's hard to believe a turtle would clamber over them and be able to dig a 50cm-deep hole.

But after poking around, Glenn determines there is a nest and we get to work. Gently brushing away the top layer of sand, I start to feel a cavity naturally developing. Its' hard to describe, but my hand seems to follow the shape of the nest as I dig. With a few more scoops, I feel an egg. I've hit the nest chamber.

One by one, we open the eggs, most of them no more than yolk. Some turtles have made it to stages two and three of the four-stage development process - indicated by the size of the embryo compared to the heart-shaped placenta it seems to embrace.

But there's no evidence of empty shells and we conclude, sadly, that no hatchling made it out alive. It's the first nest Glenn has seen in four years with 100 per cent mortality, he says.

"You need the right ingredients to 'bake a cake' - moisture, temperature and a mixture of gases circulating through the sand," Glenn says. And unfortunately, this nest was just too close to the surface, and too hot for the eggs to fully develop.

Flatback turtles need help

Most nests at this location have an 88 per cent hatch rate, though it's really unknown how many hatchlings make it to adulthood. Scientists estimate it could be as low as 1/1000. Once they hit the water, it's almost impossible to track them. They seem to disappear for a while into what researchers call the 'lost years'. It's thought they spend some of that time foraging in the northern Kimberley waters including Ashmore Reef, with foraging grounds near potential LNG developments.

It's only when they return to nesting sites like Eco Beach that researchers can study them.

With the final nest site checked for this trip, we pack up and head back to civilisation. The next group of researchers and volunteers will be back the following week to continue this important work.

It's hoped that soon, with more information about the flatback, the IUCN can formally declare the species' conservation status so that further funding and protection for this endemic species can follow.

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LINKS
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