Sky glow disrupts the orientation of Australian flatback turtles Natator depressus on nesting beaches

Light pollution may disorientate animals at night, resulting in higher mortality and lowered reproductive success. As artificial night lighting ensues from rapid coastal development, there is concern for animals that rely on natural light cues and the coastal environment, such as sea turtles. Their nesting and hatchling emergence generally occurs at night, and nearby artificial lighting can compromise their orientation. Little is known about the impact of sky glow that can be tens of kilometres away from rookeries but visible over the horizon. Here, we investigated how artificial sky glow may impact orientation of hatchling and adult female flatback turtles Natator depressus at four distinct rookeries in Australia. Two orientation parameters, how wide the tracks were spread and how much they deviated from the direct path to or from the ocean, were modelled in a circular and non-circular Bayesian framework. The effects of the moon, cloud cover, rookery, and date were considered. Misorientation of hatchlings, and to a lesser extent adult females, was detected on the rookeries where sky glow was visible from up to ~ 50 km away from the light source. The disruptive impact of the sky glow was slightly mitigated by the moon. There was no evidence of misorientation in the rookery located > 86 km away from major industrial and residential areas. The potential consequences of misorientation, including reduced fitness, are discussed. Our findings suggest careful management of coastal light pollution is imperative to prevent further disruptive impacts of sky glow on a range of sea turtle species.