Satellites and DNA reveal new insights into western Pacific’s rapidly declining hawksbill turtles

Posted on 15 August 2023

For the first time, a new study reveals that many hawksbill turtles satellite-tagged in Papua New Guinea’s (PNG)  Conflict Islands swam over 1,000 km to reach the Great Barrier Reef to forage, a journey taking more than a month. 

But hawksbills satellite-tagged in northeast Queensland’s Milman Island stayed in Australian waters, mostly 
swimming north to forage in Torres Strait and around to western Cape York, according to a separate Queensland-focused study. Both papers on the critically endangered species were recently published in Frontiers in Marine 
Science. 

The research shows the importance of safeguarding hawksbill migratory routes and foraging habitats in north-east Australia. That’s why conservationists applauded the Queensland and Australian governments’ recent commitment to phase out commercial gill nets in the Great Barrier Reef.   

“Significant numbers of hawksbills either nest and permanently live in Queensland or travel long distances to forage here. So improved protection in north east Australia and the reefs surrounding Cape York is critical to saving this species. Not just for the severely declining Milman Island population, but for hawksbill populations across the entire western Pacific,” said Christine Madden Hof, who is lead author on both papers, PhD candidate at the University of Sunshine Coast, and leader of WWF’s Global Marine Turtle Conservation programme.

“Following on from the GBR gill net phase out, now we’re keen to work with the Queensland government to 
implement net-free areas and support greater Indigenous or marine protected areas in western Cape York.  It’s clear from the satellite tracking hawksbills are heading there and our modelling shows it can be a dangerous place for a turtle,” Ms Madden Hof said. 

The Queensland study on migration patterns and threats

The Queensland study assessed the mortality risk to hawksbills. In western Cape York, where there is currently little to no protection, in large areas that risk was rated high to very high. Threats include fishing nets and ghost gear, direct harvest, and increasing sand temperatures due to climate change. 

“Our study demonstrates why gill nets had to be removed from the GBR and why new net-free areas are urgently  needed in the western Cape. There is also a clear need for greater independent scrutiny of commercial fishing in  hawksbill home ranges to give us an accurate picture of what is being caught,” said Simon Miller, a co-author of the Queensland research and Great Barrier Reef fisheries expert at the Australian Marine Conservation Society.  

Milman Island is the main nesting beach for what used to be a globally significant population of genetically distinct hawksbills known as the northeast Queensland (neQld) stock. A recent assessment of the Milman Island nesting population, co-authored by Madden Hof, revealed an alarming 58% decline over the last 28 years. It also predicts this population may be functionally extinct by 2032 if the current trajectory continues.  

Scientists fear a similar decline could also be occurring across the larger southwestern Pacific population. 

The PNG study on migration patterns and genetics 
  
Genetic sampling of females nesting in the Conflict Islands’ Group and females nesting about 1,000km further north in Kavieng revealed they are significantly different from one another and all other known Asia-Pacific stocks.

With the addition of these two, nine genetically distinct populations have now been identified in the Asia-Pacific  region, but researchers believe there are many more. They all need to be managed separately to ensure population recovery.  

“The Conflict Islands are one of the most important sites in PNG for hawksbills that we share across vast migratory routes, with Australia and other Pacific nations. We need to continue to support local communities to collectively  manage this resource for future generations to come,” said Hayley Versace,  a co-author and manager at Conflict Islands Conservation Initiative.

PNG has no legislation to protect hawksbills. But given the plight of the species that could change. 
  
“Sea turtle harvesting for shell, meat and eggs continues in PNG and the Torres Strait in Australia under the Torres Strait Treaty with no legislative or regulated quota limits. This study has highlighted the need for greater national protection for hawksbills, but given the migratory and foraging connectivity to eastern Cape York, stronger regional co-management and cooperation between the PNG and Australian Government is required,” said Vagi Rei, Manager, Marine Division, from Conservation and Environment Protection Agency of Papua New Guinea.

Notes to Editor

This is the first time satellite tracking and genetic data from PNG hawksbill turtles has been published. All threats to the northeast Queensland hawksbill stock were assessed using a combination of a post-hatchling dispersal model, new satellite tracking of post-nesting migrations and a comprehensive review of threat-based data. 

PNG Genetic data was shared to ShellBank (www.shellbankproject.org) a marine turtle traceability toolkit and global database of marine turtle DNA. Expanding the genetic baseline for marine turtles globally is a key project led by WWF in partnership with NOAA Southwest Fisheries Science Centre, Australian Museum, and TRACE Wildlife Forensics Network. 

Hawksbills tagged in the Conflict Islands migrated for between 24 to 65 days at an average swimming speed of 1.67km per hour. Their mean migration distance was 1241 km, much greater than distances revealed in most studies: Hawaii (218km), Eastern Pacific (113km), Northern Territory (349km), US Virgin Island (67km). Only the Solomon Islands (2028km) was greater. 
A satellite-tagged hawksbill in the Conflict Islands, Papua New Guinea
© Christine Hof / WWF
Route taken by hawksbills tagged in the Conflict Islands. Type refers to migratory and foraging clusters: Type I migrated to Torres Strait & FNQ, Type II migrated to Northern Qld, and Type III foraged in PNG.
© Christine Hof / WWF
Community turtle rangers with a satellite-tagged hawksbill turtle in Conflict Islands, Papua New Guinea
© Christine Hof / WWF
Locations of genetic sampling that has identified nine distinct Asia-Pacific populations; a satellite-tagged hawksbill in the Conflict Islands
© Christine Hof / WWF