Light Pollution and Sea Turtle Hatchling Orientation

By Shigetomo Hirama

Sea turtles are long-lived animals that utilize multiple developmental habitats. In all of the habitats, sea turtles encounter with various threats. Although some are naturally occurring (at least they seem to be), the majority of threats are caused by human. These anthropogenic threats in-water habitats include: fisheries’ activities, oil spills, debris ingestions, debris entanglements, boat strikes, dredging, and direct harvesting. On the beach, beach driving, artificial lighting (light pollution), armoring (sea walls, rock revetments, and other infrastructures), oil spills, and egg poaching are threats to nesting and hatchling turtles. Among these threats on the beaches, the installment of armoring structure – sea walls, rock revetments, and other infrastructures – are probably the most important threats, considering sea level rise as a consequence of climate change. Armoring structures are known to increase speed of erosion and may cause permanent loss of beach sand. Although it may not be as important, artificial lighting also is significant threats to the turtles. The artificial lighting differs from the armoring in terms of solving the issues. Coastal armoring, such as a sea wall, is difficult to remove once it is placed; however, we can change light bulb or retrofit light fixtures relatively easily. Through the present project, we provide valuable information to stakeholders to reduce hatchling mortality and increase chance of hatchlings’ survivorship.

Playalinda Beach. An example of a beach with no light pollution.

Artificial lighting alters natural illuminant environment and impacts behavior of wildlife. Nocturnal animals such as bats, moths, and some species of birds, are more susceptible to light pollution than others. Sea turtle hatchlings crawl toward ocean using the visual cues immediately after emerging from sand. The hatchlings disorient on the beach if the intensity of artificial light is relatively high and may never enter the ocean.

Cocoa Beach. An example of a beach with moderate to severe light pollution.

We have been quantifying accuracy of hatchling orientation in over the 20 Florida beaches in past five years. Hatching orientation is one of the subjects of sea turtle biology that has been studied well. Surprisingly, no known work has provided the benchmark orientation data that were collected at a natural beach and compared with the information that were collected at the beaches with varying levels of light pollution. The results of present project showed the accuracy of hatchling orientation varied widely depending on the beaches. The quantitative data of the project are currently in process of publishing in a peer-reviewed journal. In the present article, I provide photographic images that were taken by same camera, setting, and lens at the beaches with no (Playalinda), moderate to severe (Cocoa Beach), and severe (Miami Beach) light pollutions. We hope the data we provide would guide to take practical actions to reduce light pollution.

Miami Beach. An example of a beach with severe light pollution.