Abstract
Coastal areas provide critical nesting habitat for marine turtles. Understanding how artificial light might impact populations is key to guide management strategies. Here we assess the extent to which nesting populations of four marine turtle species—leatherback (Dermochelys coriacea), olive ridley (Lepidochelys olivacea), hawksbill (Eretmochelys imbricata) and two subpopulations of loggerhead (Caretta caretta) turtles—are exposed to light pollution across 604 km of the Brazilian coast. We used yearly night-time satellite images from two 5-year periods (1992–1996 and 2008–2012) from the US Air Force Defense Meteorological Satellite Programme (DMSP) to determine the proportion of nesting areas that are exposed to detectable levels of artificial light and identify how this has changed over time. Over the monitored time-frame, 63.7% of the nesting beaches experienced an increase in night light levels. Based on nest densities, we identified 54 reproductive hotspots: 62.9% were located in areas potentially exposed to light pollution. Light levels appeared to have a significant effect on nest densities of hawksbills and the northern loggerhead turtle stock, however high nest densities were also seen in lit areas. The status of all species/subpopulations has improved across the time period despite increased light levels. These findings suggest that (1) nest site selection is likely primarily determined by variables other than light and (2) conservation strategies in Brazil appear to have been successful in contributing to reducing impacts on nesting beaches. There is, however, the possibility that light also affects hatchlings in coastal waters, and impacts on population recruitment may take longer to fully manifest in nesting numbers. Recommendations are made to further this work to provide deeper insights into the impacts of anthropogenic light on marine turtles.
Highlights
The introduction and proliferation of artificial light at night has transformed the night-time environment over significant portions of our planet’s surface (Longcore and Rich 2004)
All species/subpopulations showed an increase in the proportion of nesting areas potentially exposed to light pollution (> 5.5 digital number (DN)) between the periods (1992–1996 and 2008–2012)
The human population in Brazil has grown considerably throughout the study period and much of the population growth was seen in coastal areas, where the largest urban centres are currently located (Instituto Brasileiro de Geografia e Estatística 2013)
Summary
The introduction and proliferation of artificial light at night has transformed the night-time environment over significant portions of our planet’s surface (Longcore and Rich 2004). Remote sensing has been used to measure artificial night-time light (Cinzano et al 2001) and its effects on wildlife, including invertebrates, birds, reptiles and mammals (Longcore and Rich 2004; Aubrecht et al 2008; Kamrowski et al 2012; Mazor et al 2013; Weishampel et al 2016). Worldwide measurements of artificial light have been collected by the US Air Force Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) since 1992 (Elvidge et al 2007). These data can be downloaded from the NOAA’s National Geophysical Data Center (NGDC) and represent cloud-free composite images created from multiple nightly orbits by the DMSP satellites for each year (Elvidge et al 2001, 2007)
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