Taking the heat for turtles

If it’s not turtle egg predation or choking ocean debris, threatened turtle species nesting on the West Coast of Cape York Peninsula now have to contend with warming temperatures - which are affecting the sex ratio of hatchlings. 

And as it has been called on for the past 10 years, the Western Cape Turtle Threat Abatement Alliance (WCTTAA) will be on hand to introduce ways to shade nests, lower sand temperatures and reverse the phenomena as part of their annual protection work. 

The Federal Government this week announced funding to Cape York NRM to support WCTTAA in modifying turtle nests as part of a nationwide $4.5 million investment in community projects to better protect oceans and the precious species that call them home.

“This is a great addition to the protection of threatened turtle species and will move seamlessly into the ongoing WCTTAA program and hopefully bring the nest temperatures down.” Cape York NRM Biodiversity & Fire Programs Manager, Toby Eastoe said. 

“The nesting season is just about to begin, so we will be able to trial shading at some of the sites WCTTAA protects.”

WCTTAA is a partnership of six on-ground Indigenous land and sea owners and managers which has been operating for more than 10 years with support from Cape York NRM.

Its annual turtle nest protection program covers Olive ridley, Flatback, some Hawksbill and Green turtle nests along the coastline of Western Cape York. 

WCTTAA’s work has successfully reduced turtle nest predation from 90% to 10% and sometimes less than that. They use purpose-built, rust-proof cages which are installed over nests to prevent feral animals, such as wild pigs, from attacking the eggs. 

Rangers also remove marine debris, including ghost nets, monitor the beaches and enter nest and hatchling data, carry out pre-season culling of feral animals and conduct education campaigns for the public about beach driving and camping while nests are present.

“We will be trying to influence the sex ratios of Olive ridley hatchlings to maintain a balance,” Cape York NRM’s recently appointed WCTTAA Coordinator, Dr Manuela Fischer, said. 

“Warming temperatures are producing more female hatchlings which jeopardises the Olive ridley population.”

Alarm bells about rising nest temperatures were first raised after studies conducted in 2016 and 2017 by Dr Col Limpus, together with WCTTAA’s Mapoon Rangers on Flinders Beach and Back Beach near Mapoon. 

They found that nest temperatures were greater than the predicted pivotal temperature of 29°C, except in areas on the high dune shaded by casuarinas, which can skew sex ratios, with most hatchlings expected to be female. (A pivotal temperature is that which gives approximately equal numbers of males and females.)

“We believe that by lowering the temperature in the nest, we will increase the number of male hatchlings and therefore support turtle populations in the long term,” Manuela said.

Rangers will install additional shade material over nest cages that surround Olive ridley nests as well as loggers to record sand temperatures during the nesting season. Data loggers will also be installed on a control site to compare data. 

The results of the new project won't be realised until hatchlings reach breeding age in 15-30 years' time and return to their nesting beaches. 

“Protection is long-term,” Manuela said. “The communities along western Cape York are committed and work tirelessly each year to keep these endangered species safe. 

“This project will provide valuable insights into the protection mechanisms available to bring nest temperatures closer to the pivotal temperature. We will also trial other ways to effectively shade the nests as we go forward.”

The seven key beaches protected by WCTTAA for the entire nesting season are:

• Crab Island (7 kilometres), NPARC/ Apudthama Rangers 
• Jardine River beach (10 kilometres), NPARC/ Apudthama Rangers 
• Skardon River to Namaleta Creek (28 kilometres), Mapoon Land and Sea Rangers
• Flinders Beach (24 kilometres), Mapoon Land and Sea Rangers 
• Pennefather Beach (40 kilometres), Napranum/ Nanum Wungthim Rangers
• Hersey Creek to Christmas Creek (8 kilometres), Pormpuraaw Land and Sea Management Rangers 
• Christmas Creek to Balurga Creek (22 kilometres), Pormpuraaw Land and Sea 

The Project is funded by the Australian Government’s Marine Turtle Climate Change Resilience and Nest Protection Program