To sea in the dark: assessing effects of LED streetlights on sea-finding in marine turtle hatchlings

Context Artificial light at night (ALAN) significantly affects the sea-finding ability of marine turtle hatchlings, which can entail detrimental effects on survival rates and population dynamics. Aims This behavioural study assesses the disruptive effects of light-emitting diode (LED) streetlights on the sea-finding behaviour of loggerhead and flatback turtle hatchlings. Specifically, we test LEDs that are readily available for purchase to guide wildlife-friendly lighting decisions. We examine the influence of a range of spectral wavelengths and light intensities on orientation of hatchlings post-release. Methods Behavioural experiments were conducted using a circular pitfall arena situated on a beach during the new moon to simulate natural night-time conditions. LED streetlights with narrow or broad spectral power distributions were tested at varying light intensities, which were adjusted by modifying wattage, number of LEDs, or the distance of the LED from the hatchling release point. Circular statistics were used to analyse the hatchlings’ orientation and LEDs were considered suitable for use if they did not disrupt sea-finding behaviour. Key results A narrow-spectrum LED streetlight (peak intensity at 625 nm) did not significantly disrupt hatchlings’ sea-finding behaviour, even at higher light intensities. A phosphor converted amber LED had minimal impact on flatback hatchlings but somewhat affected loggerhead hatchlings’ orientation at higher light intensities. Our findings confirm that broad-spectrum LEDs with blue wavelengths of light are not appropriate to use near marine turtle nesting beaches. Conclusions The study demonstrated the importance of understanding the spectral characteristics and intensities of artificial lighting near marine turtle nesting beaches. Narrow-spectrum LEDs without blue wavelengths of light appear to be less disruptive to sea-finding behaviour than are broad-spectrum LEDs. These findings suggest that careful selection and management of lighting infrastructure are crucial for minimising negative impacts on marine turtle populations. Implications The results have provided valuable insights for policymakers and land managers involved in coastal lighting management. Species-specific parameters should be considered when implementing lighting solutions near marine turtle nesting beaches to mitigate the adverse effects of ALAN on hatchling orientation and survival.