A participatory spatial risk assessment of green turtles (Chelonia mydas) with indigenous rangers in northern Australia

Coastal marine species and ecosystems face increasing pressure from anthropogenic threats. Green turtles (Chelonia mydas), listed as Vulnerable in Australia, are ecologically important and culturally significant for Indigenous Traditional Owners. This study co-developed a spatial risk assessment with eight Indigenous ranger groups to assess threats to green turtles in waters of Australia’s Northern Territory. Six anthropogenic hazards (comprising 11 threats) were mapped and combined with turtle occupancy, derived from the satellite tracks of 45 green turtles, to quantify threat exposure. Expert knowledge from Indigenous rangers on the impact and occurrence of 24 threats was combined to assess turtle vulnerability, generating a spatially explicit map of relative risk. Darwin Harbour had the highest concentration of overlapping threats, including artificial light, recreational vessels, oil infrastructure and shipping. Turtle vulnerability varied by region, reflecting local knowledge. Nest predation (West Arnhem, Tiwi Islands), sea-level rise, traditional hunting and industrial pollution had the highest threat scores. Foraging turtles were concentrated in eight areas, and Channel Island (Darwin Harbour) posed the highest relative risk for foraging turtles. Migration routes near Darwin Harbour and Bynoe Harbour were risk hotspots. Mixed-effects analyses showed that perceived vulnerability was structured primarily by threat type, with ranger experience contributing to variation in threat perceptions, highlighting the importance of retaining experienced Indigenous rangers for effective place-based conservation. Integrating Indigenous knowledge with spatial data, the study identifies high-risk areas for a culturally and ecologically important species and supports targeted management and sustained investment in Indigenous ranger programs amid increasing climate and industrial pressures.