Constant, N. (2015). Geospatial assessment of artificial lighting impacts on sea turtles in Tortuguero, Costa Rica. Master's thesis, Duke University, Durham, NC.
Abstract: Between June and August 2014, I conducted walking surveys to map the nesting beach
and light sources using a Trimble Juno SB GPS unit, and I developed a GIS database that formed the basis for subsequent analyses and data visualization. I built STCâs monitoring data from 2004 through 2014 into a polygon layer of the beach subdivided into mile sections defined by mile markers erected by STC. During the new moon in June and July 2014, I conducted brightness surveys in concert with STCâs light surveys and measured brightness in units of luminance at 50-meter intervals along the beach using a Unihedron Sky Quality Meter. Using spatial data of the beach and light sources, luminance data from brightness assessments, and monitoring data from STC, I determined a mean luminance value for each mile section, examined the relationship between luminance and nesting activity, and mapped light pollution on the beach.
I found that mean luminance and the total number of green turtle emergences per mile section were significantly negatively correlated. Mean luminance exceeded the minimum threshold for light pollution in 6 of the 43 mile sections, and there were significantly fewer emergences in mile sections experiencing light pollution. Mean luminance was highest in mile sections adjacent to Tortuguero Village, where sources of artificial light were concentrated. These findings were consistent with STCâs light survey data, and mean light count and the total number of green turtle emergences per mile section from 2004 to 2014 were also significantly negatively correlated. Cumulatively, these results suggest that artificial lighting from adjacent development impacts green turtle utilization of nesting habitat and changes the spatial distribution of green turtle nesting activity on Tortuguero Beach.
These results were consistent with the findings of previous studies conducted on sea turtle nesting beaches and support the need for a turtle-friendly lighting initiative in Tortuguero.