Quantifying the Impact of Light Pollution on Sea Turtle Nesting Using Ground-Based Imagery

James Vandersteen,Salit Kark,Karina Sorrell,Noam Levin

doi:10.3390/rs12111785

James Vandersteen, Salit Kark + Show 2 more

Open Access

https://doi.org/10.3390/rs12111785

Copy DOI

Abstract

Remote sensing of anthropogenic light has substantial potential to quantify light pollution levels and understand its impact on a wide range of taxa. Currently, the use of space-borne night-time sensors for measuring the actual light pollution that animals experience is limited. This is because most night-time satellite imagery and space-borne sensors measure the light that is emitted or reflected upwards, rather than horizontally, which is often the light that is primarily perceived by animals. Therefore, there is an important need for developing and testing ground-based remote sensing techniques and methods. In this study, we aimed to address this gap by examining the potential of ground photography to quantify the actual light pollution perceived by animals, using sea turtles as a case study. We conducted detailed ground measurements of night-time brightness around the coast of Heron Island, a coral cay in the southern Great Barrier Reef of Australia, and an important sea turtle rookery, using a calibrated DSLR Canon camera with an 8 mm fish-eye lens. The resulting hemispheric photographs were processed using the newly developed Sky Quality Camera (SQC) software to extract brightness metrics. Furthermore, we quantified the factors determining the spatial and temporal variation in night-time brightness as a function of environmental factors (e.g., moon light, cloud cover, and land cover) and anthropogenic features (e.g., artificial light sources and built-up areas). We found that over 80% of the variation in night-time brightness was explained by the percentage of the moon illuminated, moon altitude, as well as cloud cover. Anthropogenic and geographic factors (e.g., artificial lighting and the percentage of visible sky) were especially important in explaining the remaining variation in measured brightness under moonless conditions. Night-time brightness variables, land cover, and rock presence together explained over 60% of the variation in sea turtle nest locations along the coastline of Heron Island, with more nests found in areas of lower light pollution. The methods we developed enabled us to overcome the limitations of commonly used ground/space borne remote sensing techniques, which are not well suited for measuring the light pollution to which animals are exposed. The findings of this study demonstrate the applicability of ground-based remote sensing techniques in accurately and efficiently measuring night-time brightness to enhance our understanding of ecological light pollution.

Highlights

Artificial light is increasingly recognised as a form of environmental pollution
Moon altitude was only significant for the models in which brightness was measured using zenith photograph’s Sky Quality Meters (SQM) sector and for horizontal photograph’s landward cone of acceptance (COA) sector, in which these models demonstrated an average increase in brightness of 0.011 Vmag/arcsec2 per degree increase in moon altitude
The environmental factors of these models: the percentage of the moon illuminated, moon altitude, and cloud cover, were able to explain more than 80% of the variation in brightness measured under moonlit conditions, but cloud cover explained less than 40% of the variation in brightness measured under moonless conditions (Figure 11, Tables S6–S9)

Summary

Introduction

Artificial light is increasingly recognised as a form of environmental pollution. Ecological light pollution refers to artificial light that alters the natural light regime and adversely affects wildlife [1]. The recognition of light as a form of pollution is relatively new, and was first identified by astronomers [2]. Whilst anthropogenic impacts such as global warming, land clearing, and more tangible forms of pollution are relatively well studied, the ecological impacts of light pollution are less known [3]. Though the negative consequences of light pollution are likely far reaching and complex, a critical aspect is the direct and indirect mortality of individuals. Such events resulting from light pollution have been recorded in species of insects, birds, fish, and sea turtles [8,9,10,11]

Objectives

Methods

Results

Discussion

Conclusion