Night patrols help to save endangered species 

Caption: Hawksbill hatchlings emerging from their nest
Photographer: Xavier Hoenner

Charles Darwin University PhD candidate Xavier Hoenner will spend the next month with Indigenous Sea Rangers patrolling the shores of Groote Eylandt in search of the critically endangered hawksbill turtle.

Hawksbill turtles (Eretmochelys imbricata) were once hunted worldwide for their colourful shells to make jewellery causing a dramatic decline in numbers. Now internationally classified as critically endangered they are protected, with the largest remaining hawksbill populations living and nesting in Australia.

“Groote Eylandt, an archipelago in the Gulf of Carpentaria is a major hawksbill turtle nesting site,” Mr Hoenner said. “If we can find out more about their nesting ecology and migratory behaviour we can help to preserve their habitats.”

Last year Xavier attached satellite transmitters to the turtles to record their behaviour and found that once the nesting season finished, all the tracked turtles went out to feed at different locations along the coast of the Northern Territory.

“We think this is where they will remain for several years before migrating back to the island to lay several other clutches of eggs,” he said.

This is the first study of hawksbills in the Northern Territory, Mr Hoenner and his team will patrol the beach in search of nesting turtles to measure the adult female turtles and tag them for future identification. They will also search for hatched nests to estimate mortality rates and clutch size.

“A mature hawksbill can lay between two and six clutches of up to 180 eggs per nesting season, which lasts from June to November.

“This year seems to be a better breeding season for the hawksbills. We think the difference from last year might be related to the humidity of the sand, which can disrupt the nesting process.

“To avoid high mortality rates in sea turtle eggs the sand temperature has to be between 27 and 31 degrees.”

Mr Hoenner said that the temperature of the sand also determined the sex of the baby turtles. “Eggs incubating in temperatures between 27 and 29 degrees will result in a high proportion of males, while those in sand between 29 and 31 degrees will mostly become female turtles,” he said.

The outcomes of this research project will be used for education purposes in local Indigenous schools and to provide data for the conservation and management of hawksbill turtle habitats in the Northern Territory.

This is a collaborative project with CDU, the Northern Territory Government and the Anindilyakwa Land Council.