Sea-finding in marine turtle hatchlings: What is an appropriate exclusion zone to limit disruptive impacts of industrial light at night?

Artificial light is increasingly being recognized as a globally-significant ecological threat, but appropriate management has lagged behind that of other environmental pollutants. Industrial developments associated with the extraction of natural resources generate large amounts of artificial light. Marine turtles are particularly vulnerable to disruption from artificial light, thus effective management of lighting is critical in areas where industrial developments occur close to nesting habitat. Given the complexity of managing lighting in industry, ensuring an adequate lighting exclusion zone between the development and the beach may be the most effective strategy for limiting impacts, yet there appears to have been little focus on clearly delineating a distance which constitutes an ‘adequate’ buffer. Using arena assays, we assessed flatback turtle (Natator depressus) and green turtle (Chelonia mydas) hatchling sea-finding ability in response to three standard industrial light sources (high pressure sodium (HPSV), metal halide (MH) and fluorescent white (FW)), positioned at distances of 100, 200, 500 and 800m. Sea-finding in both species was disrupted by all three light types when lights were positioned 200m or closer, but not when lights were positioned ≥500m away. However, when shielding the lights so that light glow, but not the luminaire itself, was visible from the arena, the observed sea-finding disruption was considerably reduced. Given that facilities are typically lit by numerous luminaires, our findings demonstrate that future industrial developments should be separated from nearby nesting beaches by a buffer of at least 1.5km, as previously theorized, with all installed lighting appropriately shaded. Such measures will help minimize lighting impacts on marine turtles as extractive resource operations continue to encroach on nesting beaches around the world.