Tracking Western Australia’s flatback turtles to aid conservation

Western Australian researchers have released details of a 15-year satellite tracking program following flatback turtles as they migrate, forage and breed.

“The flatbacks can swim hundreds of kilometres,” says Dr Sabrina Fossette-Halot from the Western Australian (WA) A Department of Biodiversity, Conservation and Attractions, who has been working with flatbacks for 8 years, and turtles for two decades. Flatbacks are endemic and the survey shows they rarely leave Australian waters.

Scientists attached satellite transmitters to 308 flatback turtles (Natator depressus), in the Pilbara and the Kimberleys in northwest WA, between 2005 and 2020.

The results are published in Ecosphere.

“This work represents a significant step towards understanding the movement of flatbacks across the northern waters of Australia as a whole; a challenging part of the world to access even at the best of times!” says Fossette-Halot.

The satellite tracking showed a “migratory corridor ” along the WA coastline between Eighty Mile Beach north to the Kimberley – a rughly 800km stretch. Turtles tagged across the state remained relatively close to shore. Some ventured into the Northern Territory, even as far as the Gulf of Carpentaria.

Females swim from their Pilbara rookeries to the Kimberley to forage and return 1 or 2 years later to breed. But some swam an amazing 11,000km. “Not in a straight line,” says Fossette-Halot, an author on the paper. One was tracked swimming for 820 days. They mostly swam in a water column at 20 to 25m depth.

“We did this survey analysis during COVID when the WA borders were closed, and discovered that most flatbacks didn’t cross the borders,” she laughs. That’s unusual for marine turtles which are known to swim across oceans.

This dataset provides valuable, detailed distribution information for a species about which relatively little is known. Because the flatback turtles occupy remote waters, Fossette-Halot says, for example, the population size isn’t known. “We survey the females when they come up on the beach but we do not have easy access to males and juveniles. An estimate for WA is about 27,000 female flatbacks nesting every year.”

There is also uncertainty about their food sources although it’s probably soft-bodied invertebrates such as sea cucumbers, sea pens, cuttlefish but also soft corals, sponges and jellyfish.

“But their specific diet remains something of a mystery,” says Fossette-Halot. “Green turtles and other turtle species regularly wash up on shore and you can look at their gut content, but very few flatbacks turn up on shore, freshly dead, potentially because their foraging grounds contain lots of predators and as soon as they die, they’re eaten.”

An understanding of the distribution and habitat use patterns of a vulnerable species like the flatback is key to informing conservation strategies.

The turtles which nest in the Pilbara share their habitat with some of the world’s biggest oil and gas developments. The authors write in the paper: “…the North West Shelf has been identified as an area of very high cumulative threats linked to industrial development.”  

Flatback turtles in the Kimberleys are in more remote and pristine waters.

Although this tracking survey was conducted solely on WA flatbacks, the species lives right across the northern coast and has been subject to other research (here with other tracking surveys : here, here, here and here.)

The flatback turtle and climate change