EuroTurtle - Photopollution

The issue of reducing disturbance to sea turtles on the nesting beach is not a simple as choosing a light that does not affect sea turtles (which, by the way, can be any light that happens to be turned off). Lurking about on a beach can disturb nesting turtles, lights or no lights. Some nesting sea turtles are more sensitive to this "human presence" than are others. For instance, green turtles and loggerheads that have just emerged from the sea nearly always respond to a human approaching within the turtle's field of view by withdrawing their necks, pivoting, and returning to the sea, whereas olive ridleys are known to complete their nesting even after being plucked from the sea as they emerge, carried up the beach, set in the sand, and watched intently by an audience of egg collectors (please do not try this at home).

Most sea turtle researchers quickly come to know how closely they can approach the turtles that nest on their beach but may wonder if the use of light by workers on the beach may frighten turtles they cannot see. I have found that lighting on the beach will keep loggerheads and green turtles from emerging to nest, but once these turtles emerge to nest, a moving person without a light is more likely to cause nesting abandonment than a motionless person with a light.

Although lights that cause nesting turtles to abandon nesting attempts are bad, lights that cause hatchlings to move in the wrong direction and die are probably worse. Generally, the longer a light is left on the greater the harm it can cause hatchlings (the longer they may travel in the wrong direction).

So how can one travel, work, and see one's way on a sea turtle nesting beach while minimizing harm to sea turtles? I have the following tips (generally supported by evidence but open for debate).

Use light sources that are pure red and use them only briefly. Pure red light (light that is composed mostly of wavelengths in the red region of the visible spectrum) is preferred for two reasons. The first is that sea turtles apparently do not see red light as well as we do. The second reason is that red light does not bleach the photopigment we depend upon for our night vision. Consequently, one can use a red light briefly to fill out a data form and still be able to see in the dark when the light is turned off. Not all reds are the same. Some are more pink (whiter than red) to begin with and some start out red but fade to purple (blue and red) over time. One of the most pure and fade resistant red filters I have found is the red plastic (lexan) of automobile tail lights (the lens can be cut to flashlight-size with a coping saw and the entire light fixture can be mounted on an ATV). In the USA, some makers of small flashlights offer a red lens that also is very good. I have also seen small lights with tiny red LED (light emitting diode) lamps that are very very good (these are often termed map-reading lights). Most red films of acetate that one might use to cover a flashlight fade quickly and because of this are not very good. Red tape is fair in a pinch but it diffuses the light too much to focus it well.
Don't fear the dark. Most people are surprised by how well they can see at night without artificial lighting. After about twenty minutes in the dark (or under a red light) the human eye can see well enough to keep its owner from tripping on even the darkest of nights. If the moon is out, one may even read a wristwatch. Eat carrots. Losing a dependence on artificial light will allow one to see well beyond the flashlight beam. Believe it or not, one can generally see the silhouette of a turtle at a greater distance without a flashlight.

Blair Witherington
Florida Marine Research Institute
Tequesta Field Laboratory
19100 Southeast Federal Highway
Tequesta, Florida 33469 USA