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<p>Artificial lighting on sea turtle nesting beaches repels adult females searching
for nest sites and disrupts hatchling seafinding, with potentially substantial effects
on nesting activity and hatchling survival. Artificial lighting is one of a host of
anthropogenic threats, including intentional harvest, bycatch in fisheries, interaction
with marine debris, and habitat degradation, that have contributed to global sea turtle
population declines. Because artificial light on nesting beaches has the potential
to impact sea turtle life history stages that are essential to reproductive success,
managing artificial lighting is a vital component of nesting beach protection. Furthermore,
identifying nesting beach habitat vulnerable to the effects of artificial lighting
is critical to guiding conservation efforts that aim to protect sea turtle populations.</p>
<p>Green turtles (Chelonia mydas) are classified as endangered globally by the International
Union for Conservation of Nature (IUCN). Tortuguero Beach in Costa Rica supports the
largest green turtle nesting population in the Western Hemisphere, with more than
one hundred thousand green turtle nests laid on the beach every year. The Sea Turtle
Conservancy (STC) has monitored and worked to protect the nesting population since
1959, and since 2004, the organization has conducted surveys to monitor artificial
lighting on the beach. The primary objective of this project was to support the Sea
Turtle Conservancy’s efforts by:
<ol><li>1) Assessing the effect of artificial lighting from adjacent development on
green turtle nesting in Tortuguero,</li>
<li>2) Mapping artificial lighting on the beach in order to identify the brightest
areas as appropriate targets for light pollution reduction efforts, and</li>
<li>3) Developing a geographic information system (GIS) database to facilitate future
monitoring and beach protection by STC.</li></ol></p> <p>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 STC’s 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 STC’s 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.</p> <p>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 STC’s 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.</p>
<p>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. Successful management of light pollution on Tortuguero Beach will require
a coordinated effort between the Sea Turtle Conservancy, the Costa Rican Electricity
Institute (ICE), and local stakeholders. I made the following recommendations for
addressing light pollution in Tortuguero:
<ol><li>1) Light pollution management efforts should focus on Tortuguero Village,
where the majority of light sources are found and luminance was highest.</li>
<li>2) Light pollution management should involve both restoration of native beachfront
vegetation and improvements in lighting technology.</li>
<li>3) Future brightness surveys to document reduction of light pollution in response
to STC’s efforts could focus on mile sections adjacent to Tortuguero Village. Brightness
data from this study provide a baseline against which to compare future brightness
levels on the beach.</li>
<li>4) Targeted monitoring of hatchling disorientation near Tortuguero Village would
provide additional insight into artificial lighting impacts on the nesting population
and help identify specific lights that continue to be problematic after management
actions are taken.</li></ol></p>
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