How many sea turtle nesting hotspots were potentially exposed to artificial light?

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Coastal areas provide critical nesting habitat for marine turtles, and understanding how artificial light might affect their populations can help guide management. Researchers assessed exposure to light pollution across 604 km of the Brazilian coast for nesting populations of four species: leatherback (Dermochelys coriacea), olive ridley (Lepidochelys olivacea), hawksbill (Eretmochelys imbricata), and two subpopulations of loggerhead turtles (Caretta caretta).

They used yearly nighttime satellite images from the US Air Force Defense Meteorological Satellite Programme (DMSP) for two five-year periods, 1992–1996 and 2008–2012, to determine the proportion of nesting areas exposed to detectable artificial light and how exposure changed over time. During the monitored period, 63.7% of nesting beaches experienced an increase in nighttime light levels. Based on nest densities, the researchers identified 54 reproductive hotspots, 62.9% of which were in areas potentially exposed to light pollution.

Light levels appeared to have a significant effect on nest densities of hawksbills and the northern loggerhead stock, although high nest densities were also seen in lit areas. The status of all species and subpopulations improved over the period despite increased light levels. The findings suggest that nest site selection is likely determined primarily by factors other than light and that conservation strategies in Brazil appear to have successfully contributed to reducing impacts on nesting beaches.

However, light may also affect hatchlings in coastal waters, and effects on population recruitment may take longer to fully appear in nesting numbers. The researchers made recommendations for further work to gain deeper insight into the impacts of human-made light on marine turtles.