The Effect of Artificial Light on Orientation of Hatchling Loggerhead Sea Turtles (Caretta caretta)

Sea turtle hatchlings primarily use sight to detect differences in the angle of elevation in relation to the beach as well as light intensity present along the horizon to navigate from the nest to the water’s edge. Artificial lights can cause visual disorientation (aimlessly wandering in circular paths around the nest) or misorientation (moving in distinct paths away from ocean). Several studies have been conducted on the effects high levels of light pollution associated with major cities can have on hatchling sea turtle orientation, whereas few studies have been done on the effects of comparatively lower levels of light pollution associated with rural areas, which are often considered ideal nesting habitats. This study examined lower light intensity found in areas surrounding large cities to identify if there is a threshold of light pollution above which hatchling orientation is negatively affected. During the 2016 nesting season, a Geovision GV-FER5303 non-illuminating infrared camera recorded hatchling trajectory at 21 Loggerhead Sea Turtle nests from areas varying in light intensity along the Grand Strand region of South Carolina. Fan spread, orientation deviation, and average crawl speeds were measured from each nest to determine if parameters associated with sea-finding behavior were significantly affected by radiance conditions present at the time of emergence. Average crawl speeds were significantly influenced by radiance conditions, with faster average crawl speeds recorded for nests emerging under conditions when moonlight was present, and lower average crawl speeds recorded under low and high levels of light pollution. Studies that examine how sea-finding behavior could be altered, even in areas of relatively low radiance, can help inform management practices to enhance hatchling survival.