Gulf Islands National Seashore (GINS) stretches across 160 miles of coastline along the Gulf of Mexico. Four species of endangered sea turtles and one species of threatened sea turtle inhabit this region, and the beaches of GINS are often used by these species for nesting. Rapid urban growth in and around GINS over the last century has contributed to increased light pollution on its beaches. Light from anthropogenic sources on the beach is thought to negatively influence the placement of nests by adults (e.g., below the tide line where nests flood) as well as cause hatchling disorientation so they fail to move toward the Gulf of Mexico. Our objectives in this study were to assess the effects of ambient visible and blue wavelength light on nest placement by adults (poor placement required nest relocation) and hatchling disorientation. We accomplished this by recruiting citizen scientists and equipping them with Sky Quality Meters (SQMs) and laser pointers to take complete hemispheric nighttime light and horizon altitude measurements at laid and hatched nests. Nest relocation and hatchling disorientation were recorded as binary variables and were modeled as a function of SQM and horizon altitude measurements using logistic regression.
Results/Conclusions
During the 2014 field season 79% of the nests needed relocation. For the non-relocated nests, 90% hatched at least one young and for the relocated nests, 92% hatched at least one young. Of the non-relocated nests that hatched, 56% had disoriented hatchlings, and of the relocated nests that hatched, 37% had disoriented hatchlings. For the nest relocation analysis the model best supported by the data included a single term for the difference in the maximum blue wavelength light intensity measured in the south (toward the Gulf) and north (toward urban centers) directions. The estimated parameter indicated the probability a nest needed to be relocated increased as the difference increased (p = 0.0720). For the hatchling disorientation analysis, the model best supported by the data had additive terms for lunar phase and blue light intensity to the north (toward urban centers). As the phase of the moon increased from 0% to 100%, the probability of disorientation decreased (p = 0.0017), and as blue light intensity to the north increased disorientation increased (p = 0.0389). These results suggest reducing blue wavelength light pollution from anthropogenic sources could improve sea turtle nesting habitat. All data reported are preliminary.