Gumbo Limbo Nature Center Scientists Study the Effects of Sky Glow on Hatchling Sea Turtles
Kirt Rusenko, Ph.D.
I was honored to be a presenter at the recent International Dark-Sky Association’s Annual General Meeting this November during the session entitled “Artificial Light at Night: Impacts to Reptiles”. It has long been known that artificial light at night (ALAN) can deter nesting female sea turtles and disorient their hatchlings. Boca Raton has proven to be an excellent field laboratory to study ALAN sky-glow impacts on sea turtles because it is located in a very urbanized area and literally half of the linear beachfront comprised of unlit park areas. Development increases significantly immediately south of Boca Raton in Broward County resulting in a more intense sky-glow in that direction.

Applying a technique known as the “hatchling orientation index” to the crawls of sea turtle hatchlings from emerged nests we were able to determine the overall direction the hatchlings took to the ocean. Results from this nesting season showed loggerhead hatchlings from Boca Raton beaches approached the ocean in a more southeast direction and
Circular charts reveal both the direction and overall scatter of hatchlings as they traverse the beach. Dark beaches enable efficient seafinding (left); lighter beaches cause scatter (right).
not direct to the ocean. In Boca Raton the ocean was largely east-northeast or 80 degrees while the hatchlings path to the ocean was almost southeast or 122 degrees. We had long noted a southward direction for our hatchlings and even the adults, this was the first time we were able to quantify it.

Hatchlings from less developed areas such as Juno Beach took a more direct route to the ocean. This indicates that the more intense sky-glow from major cities south of Boca Raton may be influencing the sea finding capabilities of
hatchlings even when they are not considered to be disoriented by lights. Additional studies using GPS locations of sea turtle nests and non-nesting emergences demonstrated the importance of beach width and dune height on the behavior of nesting females.
South Florida’s coast at night, as seen from space.
Using a device to measure the height of the dune as an angle in degrees from the high water line we found that an angle of 10 degrees or less resulted in significantly more adult false crawls in that area. Additionally, as the beach width increased from 50 feet to 250 feet there was a linear increase in the number of adult false crawls up to about three false crawls per nest at 250 feet beach width. Normally a loggerhead sea turtle has one false crawl for every nest, more false crawls than nests indicates that the emerging turtles are not happy with their beach.

Data collected in the past 15 years show that sea turtle nesting activity in Boca Raton is shifting from our unlit park areas to nesting habitat in from of large (tall and wide) beachfront condominiums. These buildings shade the beach from the sky-glow of the development inland, creating more desirable nesting habitat. For the last two years our only hotel on the beach has had a higher density of nests per mile than Red Reef Park which has been the favored nesting site in the past. While this demonstrates good compliance with the lighting ordinance, it is disturbing to see sea turtles vacating the more natural areas of the beach. I hope in the future more people realize the negative impacts of ALAN and will start encouraging lighting ordinances that cover the entire land area, not just the beachfront in order to reduce sky-glow.
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