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

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.

Multiple Angle Observations Would Benefit Visible Band Remote Sensing Using Night Lights

“…One example where this is likely helpful is in the study of ecological light pollution (Longcore & Rich, 2004). Animals generally do not view the world in nadir view, but rather look forward and to the side (Vandersteen et al., 2020; Van Doren et al., 2017). Information about how lights appear in the forward view is therefore important for understanding animal attraction.…”

X,Y, and Z: A bird's eye view on light pollution

“…Measuring light pollution remains a complex challenge, which can be seen from a number of recent publications (Kolláth et al, 2021 ; Kyba et al, 2022 ; Levin et al, 2019 ; Masana et al, 2021 ). For example, investigating the impact of ecological light pollution on the behavior of living organisms is challenging since ambient lighting conditions can change rapidly and vary considerably between places (Cinzano & Falchi, 2012 ; Jechow et al, 2017 ; Vandersteen et al, 2020 ). Therefore, it is extremely challenging that the resolution in time and place is not a strength of today's satellite‐based remote sensing systems (Kolláth et al, 2021 ; Kyba et al, 2022 ; Levin et al, 2019 ; Vandersteen et al, 2020 ).…”

“…For example, investigating the impact of ecological light pollution on the behavior of living organisms is challenging since ambient lighting conditions can change rapidly and vary considerably between places (Cinzano & Falchi, 2012 ; Jechow et al, 2017 ; Vandersteen et al, 2020 ). Therefore, it is extremely challenging that the resolution in time and place is not a strength of today's satellite‐based remote sensing systems (Kolláth et al, 2021 ; Kyba et al, 2022 ; Levin et al, 2019 ; Vandersteen et al, 2020 ). Additionally, it is problematic that today's systems cannot detect light visible to birds, insects, and bats (Briscoe & Chittka, 2001 ; Cuthill et al, 2000 ; de Miguel et al, 2021 ; Winter et al, 2003 ).…”

Pervasiveness of Biological Impacts of Artificial Light at Night

“…The biological impacts of ALAN in marine systems seem likely to be at least as diverse as those occurring terrestrially, with evidence already for effects on timing of coral spawning ( Ayalon et al 2020 ); invertebrate settlement ( Davies et al 2015 ); behavior of pelagic organisms ( Berge et al 2020 ); turtle nesting and orientation ( Thums et al 2016 ; Silva et al 2017 ; Hu et al 2018 ; Vandersteen et al 2020 ); and seabird grounding and mortality ( Wiese et al 2001 ; Le Corre et al 2002 ; Jones and Francis 2003 ; Rodríguez et al 2014 ; Syposz et al 2018 ). Impacts on diel vertical migration of zooplankton could be especially profound, given its importance for global carbon cycling.…”