How does artificial light affect baby flatback turtles heading out to sea?

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Newly hatched sea turtles entering the water are thought to use wave cues to orient away from shore. Artificial light may interfere, but the relative importance of natural and human-made cues to hatchling dispersal was unknown.

Researchers used acoustic telemetry to track flatback turtle (Natator depressus) hatchlings moving through nearshore waters. The turtles dispersed with and without artificial light through an array of receivers where various oceanographic variables were measured. Their tracks were analyzed using a full-subsets generalized additive mixed model approach to identify the most important cues affecting bearing, variance in bearing—a measure of their ability to orient directly—travel rate and time spent in the array.

Regardless of oceanographic conditions, artificial light reduced swim speed by up to 30%, increased time spent in nearshore waters by 50–150%, and made bearing 100–180% more variable. Under ambient conditions, ocean currents affected the hatchlings’ bearing as they left shore. With light present, that effect diminished, showing that the turtles actively swam against currents in attempts to move toward the light.

After accounting for currents under ambient conditions, the researchers found that the hatchlings swam offshore perpendicular to the coastline and did not appear to orient into the direction of incoming waves. Overall, light disrupted dispersal, causing hatchlings to linger and become disoriented near shore and expend energy swimming against currents.