Light Pollution: the Invisible Threat to Sea Turtles

Light pollution on a sea turtle nesting beach
Intense light pollution on a sea turtle nesting beach

Sea turtles lay their eggs on their nesting beaches and have no further contact with their offspring. The nests incubate in the warm sand for up to two months. After they hatch from the eggs, hatchlings dig their way upwards through the sand during the night, when the sand is cooler. They reach the surface alone or in groups, quickly crawl towards the sea, and swim away to the open sea in a frenzy. Less than one in a thousand will survive and one day return to the same area to reproduce.

How do these hatchlings, which are so little and have never before seen the world, manage to immediately locate the shortest path to the sea? This seemingly innate ability has excited nature-lovers and researchers for decades. Early observation and scientific studies in the last few decades give us a nearly complete understanding of this phenomenon:

A disoriented hatchling squashed by a car
Disoriented sea turtle hatchlings attracted by street lights easily end up on the road, where cars can squash them or they become easy prey for dogs, cats, foxes, or birds.

On a natural, dark beach, the horizon above the sea is slightly brighter than the horizon above land. Hatchlings can detect this difference and find the quickest path to the sea. While light orientation has helped them for millions of years, this imprinted orientation behaviour is now threatening the survival of sea turtles.

Light pollution distorts this natural ambient light pattern and confuses hatchlings. Instead of crawling to the sea, they either head towards the lights or crawl in circles and get lost on the beach. Hundreds of hatchlings are found dead on the nesting beaches of Greece, and many more disoriented tracks are recorded every year. In some cases, hatchlings have been found under lamps, trying to climb towards them. Hatchlings do not have the ability to think that they are doing something wrong; they simply crawl towards the brightest light, and this often leads them to death.

A sea turtle nest shaded from light pollution
As a temporary solution, nests can be shaded to stop hatchlings from moving towards artificial lights and help them find the sea.

On the sea turtle nesting beaches of the United States, where the problem is well understood and recognized, regulation is in place to control light pollution. Home and business owners are required to only use low-intensity specialized and shaded lights. No light is allowed to be visible from the beach, and street lights are replaced with lights that are shaded or embedded into the street.

Similar regulation is in place in most regions around the world where sea turtles are nesting. These regulations, however, are rarely implemented, and it is left to local residents or conservation field workers to deal with the problem, leaving much room for conflict and misunderstandings.

In Greece, guidelines to protect sea turtle hatchlings from light pollution were issued by the Department of Environmental Planning of the Ministry of Environment more than a decade ago. These, however, were issued in a letter to local authorities, and the guidelines were not perceived as compulsory. The problem of light pollution is little understood by local authorities. On the other hand, environmentally aware locals who often find hatchlings lost and killed due to light pollution are confused about who they need to inform about the problem and who has the authority to enforce the guidelines.

Embedded roadway lights can reduce light pollution
Embedded roadway lights are an alternative to street lamps and are not visible from nearby beaches. They are ideal for streets where only street visibility for drivers is required.

While the only suitable solution is to eliminate light pollution, field workers have to rely on makeshift methods to reduce hatchling disorientation. On the nesting beaches of Crete, the Peloponnese, Zakynthos, and Kefalonia, where conservation projects operate every summer, volunteers place mats around nests affected by light pollution to shade them from nearby lights. This helps hatchlings find the way to the sea.

When light pollution is intense, however, this method is often not enough. On the beach of Kalo Nero, near Kyparissia, volunteers place boxes over hatching nests to trap hatchlings and move them to a dark part of the beach, where they can safely crawl to the sea. This is an extreme protection measure which should not have to be used, because it is unknown whether it has negative effects to hatchlings and it has a great operational cost to the volunteers, but it is currently the only way to effectively reduce hatchling mortality from light pollution.

The notion that controlling light pollution is an obstacle to development is a misconception. The guidelines mentioned earlier clearly mention that “these problems can be controlled without prohibiting the use of the beach.” Lights can easily be shaded, turned downwards, and dimmed down. Specialized amber lights, which have a much lower disorientation effect on hatchlings, can be installed where they are necessary for public safety. These methods may not always solve the problem, but they will certainly be a significant improvement.

Dimly lighted streets and pathways are in most cases preferable to strongly illuminated ones, because they offer residents and visitors a peaceful relaxing environment in which they can enjoy the view of the sea and the night sky. As for driving cars, embedded street lights or reflectors and a low line of light barriers will reduce disorientation dramaticlaly and possibly reduce costs. Misconception and miscommunication are the only obstacles to protecting hatchlings from light pollution.

Written by Nikos Vallianos | .