Turtle hatchlings. Credit: Suzanne Long (AIMS)
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The impacts of artificial light on marine turtles

Friday, 13 December 2019  | 

Six of the world’s seven marine turtle species occur in Australia and all are protected by international and national agreements and legislation. Light pollution in the coastal zone is considered a key threat to marine turtles.

In Australia, a large number of important turtle nesting sites are exposed to light pollution along the industrialised Northwest Shelf of Western Australia and the urbanised coast of Queensland. Marine turtle hatchlings generally emerge from their beach nests at night and show an innate ability to orientate towards the sea, being attracted toward the lower, brighter horizon of the sea surface.

Artificial lighting along the coast can confuse and misdirect newly emerged hatchlings by appearing brighter than the sea surface horizon. This can result in hatchlings being attracted away from the sea, increasing their risk of death by predation, dehydration or exhaustion. If hatchlings reach the ocean, artificial light on and around water (e.g. boats at anchor, jetties) can continue to disorientate them, potentially causing them to linger in nearshore waters with similar results. There is also evidence that light pollution can disrupt and deter the nesting behaviour of adult female turtles.

To reduce the impacts of lights on turtles, the Commonwealth Department of Environment and Energy is developing guidelines to manage artificial light around wildlife. The guidelines outline best practice lighting design including starting with natural darkness and only adding light when needed, and using smart controls (motion sensors, timers, etc). They recommend lowering light intensity and avoiding lights with blue wavelengths, which are particularly disruptive to turtles. Further, lights should be kept close to the ground, directed and shielded and surfaces should be non-reflective.  The implementation of these recommendations to new and existing projects near turtle nesting beaches will reduce the impacts of artificial light on marine turtles.

Research Entries

Mazor T., Levin N., Possingham H. P., Levy Y., Rocchini D., Richardson A. J. & Kark S. (2013) Can satellite-based night lights be used for conservation? The case of nesting sea turtles in the Mediterranean. Biological Conservation 159, 63-72.
To examine the influence of night time lighting on sea turtle nesting distribution over a 19 year period using satellite imagery obtained at two different spatial resolutions
The total number of turtle nests and occupancy (presence/absence) was lower in areas with night lighting, particularly in areas where light was brightest. There were more nests and occupancy was higher in darker sections of the coastline. Satellite imagery at higher resolution was slightly better at detecting a difference; however the lower resolution imagery still detected an effect of light on nesting behaviour. In addition to light, human population density and infrastructure negatively influenced turtle nesting and occupancy, but the presence of cliffs had a positive influence.
Witherington B. E. (1992) Behavioral responses of nesting sea turtles to artificial lighting. Herpetologica 48, 31-39.
To examine the effects of two light types on the nesting behaviour of green and loggerhead turtles
Green and loggerhead turtle nesting was significantly reduced in areas lit with mercury vapour lamps but low pressure sodium lights did not significantly influence nesting behaviour of either species. Nesting density (emergences/km/night) was lower for both species in the area illuminated with mercury vapour lights but there was no significant difference in density between the control and low pressure sodium group. Five turtles were misdirected by lights upon return to the water, mostly during the mercury vapour treatments, but they were all able to return to the ocean without assistance.
Price J. T., Drye B., Domangue R. J. & Paladino F. V. (2018) Exploring the role of artificial lighting in loggerhead turtle (caretta caretta) nest-site selection and hatchling disorientation. Herpetological Conservation and Biology 13, 415-422.
To examine the effects of light illuminance levels on nest site-selection and hatchling disorientation of loggerhead turtles
Higher levels of landward illuminance resulted in lower nesting activity and a lower number of nests laid, particularly when brightness levels exceeded 800 µcd/m². The authors also found a significant relationship between landward illuminance values and hatchling disorientation, but there was no obvious threshold found.
Wilson P., Thums M., Pattiaratchi C., Meekan M., Pendoley K., Fisher R. & Whiting, S. (2018) Artificial light disrupts the nearshore dispersal of neonate flatback turtles Natator depressus.Marine Ecology Progress Series 600, 179-192.
To determine the effects of two types of artificial light on the nearshore dispersal of flatback turtle hatchlings and the relative importance of natural and artificial cues on this process.
Artificial light disrupted the dispersal of flatback turtle hatchlings at sea. Metal halide lighting was more disruptive than high pressure sodium but both sources of lighting reduced their swim speed and increased how long they spent in nearshore waters. Hatchling swimming trajectories were largely influenced by ocean currents under ambient conditions, but when lights were present, hatchlings swam against these currents to get to, and linger at the light source, potentially resulting in energetic consequences and increasing their risk of predation.
Wilson P., Thums M., Pattiaratchi C., Whiting S., Pendoley K., Ferreira L. C. & Meekan M. (2019) High predation of marine turtle hatchlings near a coastal jetty. Biological Conservation 236, 571-579.
To assess the impact of a jetty with artificial lights on the predation rates and movement patterns (using acoustic tracking devices) of flatback turtle hatchlings as they swim through the nearshore zone.
Hatchling predation was high near a jetty, regardless of the presence or absence of artificial light. A number of hatchlings tagged with acoustic tracking devices were consumed by fish predators, allowing the authors to track the predator's movements. Tracks revealed that these predators were using the jetty as a daytime refuge, and dispersing along nearshore waters at night to prey on hatchlings, particularly in an area adjacent to where turtle nesting was concentrated. Predation of hatchlings was much higher at this location than an unmodified (no jetty) section of coastline nearby.
Weishampel Z. A., Cheng W-H. & Weishampel J. F. (2016) Sea turtle nesting patterns in Florida vis-à-vis satellite-derived measures of artificial lighting. Remote Sensing in Ecology and Conservation 2, 59-72.
To assess trends in light levels and its effects on turtle nesting behaviour over a 21-year period at different scales
Over the 21-year period, most (67.7%) nesting segments showed a decrease in light levels over time. There was also a general increase in nesting for all three species over this period. Despite this, nesting densities were lower in beach segments with artificial light for green and loggerhead turtles, but not for leatherback turtles.
Kamrowski R. L., Limpus C., Moloney J. & Hamann M. (2012). Coastal light pollution and marine turtles: assessing the magnitude of the problem. Endangered Species Research 19, 85-98.  
To assess the proportion of marine turtles in Australia potentially at risk from light pollution.
In Australia the majority of nesting turtles appear to be at low risk but the industrialised coast of WA (e.g. north-west shelf) and the urban coast of Qld contains globally significant turtle populations that have high proportions of nesting areas exposed to light pollution (24 – 60%). Species most at risk are hawksbill, flatback, green and loggerhead turtles. The risk to turtles from light generated by industrial developments in WA appears significantly higher than at any other location.
Thums M., Whiting S. D., Reisser J., Pendoley K. L., Pattiaratchi C. B., Proietti M., Hetzel Y., Fisher R. & Meekan M. G. (2016) Artificial light on water attracts turtle hatchlings during their near shore transit. Royal Society Open Science 3, 160142.
To examined the effect of artificial light on water on the near shore trajectories of turtle hatchlings dispersing from natal beaches.
Turtle hatchlings dispersing from shore are influencedby artificial light. 88% of individuals swam towards the experimental lights on a boat at anchor and spent, on average, 23% more time in the nearshore zone than under ambient light conditions, potentially increasing their risk of predation.
Lorne J. K. & Salmon M. (2007) Effects of exposure to artificial lighting on orientation of hatchling sea turtles on the beach and in the ocean. Endangered Species Research 3, 23-30.
To determine whether turtle hatchlings that have been previously misoriented by artificial lighting (attracted landward instead of seaward) can later recover from that experience, and orient normally to find the sea and swim away from the shore from a dark beach. This is needed because misoriented or disoriented hatchlings are sometimes found alive on the beach, either late at night or the morning after failing to locate the sea and some guidelines (in this case, Florida Fish and Wildlife Conservation Commission guidelines) recommend that these hatchlings should be moved closer to the water, or released in shallow water near the shore.
A brief (2 min) exposure and attraction landward to lights had no effect on hatchlings subsequently finding the sea andswimming away from shore as long as surface waves were present. In a calm sea they failed to swim offshore. A long (2 h) exposure and attraction toward a landward light source, however, impaired the ability of the turtles to crawl on straight paths to the sea, and lengthened the time taken to reach the surf zone. The results demonstrated that orientation landward toward artificial light sources compromises the ability of hatchlings to respond naturally to the cues normally used to locate the sea.
Harewood A. & Horrocks J. (2008) Impacts of coastal development on hawksbill hatchling survival and swimming success during the initial offshore migration. Biological Conservation 141, 394-401.
To investigate of the impacts of beach lighting on hatchling predation rate and swimming success during the initial swim away from shore
The overall predation rate was low (6.9%) and it was not significantly affected by beachfront lighting. However, of those hatchlings leaving lighted beaches that successfully escaped predation, a significantly smaller percentage (32.9%) were able to swim the prescribed distance seawards during the observation period. Moonlight significantly improved the swimming success of hatchlings leaving lighted beaches, particularly when the moon was full, but also significantly influenced predation rates, which were highest during the full moon (12.6%). These results suggest that artificial lights emanating from a landward direction, although not increasing predation measurably, may still interfere with hatchlings’ escape away from the nearshore and into deeper waters, even with natural moon light. Some hatchlings released from dark beaches were attracted by lights from neighbouring beaches once they became visible after hatchlings were a substantial distance from shore.
Erb V. & Wyneken J. (2019) Nest-to-surf mortality of loggerhead sea turtle (Caretta caretta) hatchlings on Florida’s east coast. Frontiers in Marine Science 6, 1-10.
To quantify the mortality of loggerhead hatchlings on their crawl from nest to sea and to identify the sources of the mortality at a number of different sites on Florida's east coast
Out of 66 nests, 7.6% did not survive to reach the water (4.2% likely mortalities, 3.4% confirmed mortalities). Ghost crabs were the most common predator and also night heron. Mortality was highest at Boca Raton (44%), a highly urbanized site but the largest cause of mortality was not predation, it was mis or disorientation due to light pollution. Predation was the next largest cause. The factors identified as important in hatchling mortality included numbers of hatchlings emerging, nest-to-surf distance, and level of urbanisation. Nest-to-surf distance, total number of hatchlings emerging and urbanization best predictors of mortality, as well as location. Small numbers of emergence was associated with higher rate of predation. Greater nest-to-surf distance resulted in higher predation. More lighting resulted in more predation. Potential that light attracted more predators?
Limpus C. & Kamrowski R.L. (2013) Ocean-finding in marine turtles: the importance of low horizon elevation as an orientation cue. Behaviour 150, 863-893.
To document the importance of horizon cues for ocean-finding in hatchlings under natural field conditions.
1. Hatchlings move towards the horizon line at the lowest angle of elevation. 2. Hatchings move away form high silhouettes, in a direction that remains close to the horizon line at the lowest angle of elevation3. where a conflict exists regarding the direction of the lowest horizon elevation, hatchlings move towards the brightest lowest horizon
Salmon M., Wyneken J., Fritz E. & Lucas M. (1992) Seafinding by hatchling sea turtles: role of brightness, silhouette and beach slope as orientation cues. Behaviour 122, 56-77.
To assess the effects of visual and slope stimuli, alone and in combination, on green and loggerhead hatching seafinding.
In an arena set up, both species oriented towards the brightest horizon and oriented away from tall dark silhouettes, at or near eye level. The silhouette cue overrode the light cue when offered competing cues. Slope was a poor cue in orientation.
Witherington B. E. & Bjorndal K. A. (1991) Influences of wavelength and intensity on hatchling sea-turtle phototaxis: implications for sea-finding behavior. Copeia 1991, 1060-1069.
To assess the preferences for light intensities and colour on loggerhead and green hatchlings during sea finding.
Both species oriented towards uv, violet and blue-green light (360, 400 and 500 nm) and the number of hatchlings attracted increased with increasing intensity. When offered dark vs colour at high and low intensity, loggerheads moved towards 360, 400 and 500 nm and away from 560, 580 and 600nm (orange light). Loggerheads only moved towards red 700nm light at high intensities. Green hatchlings didn't respond to 600 and 700 nm at either high or low intensity
Pendoley K. & Kamrowski R. L. (2015) Influence of horizon elevation on the sea-finding behaviour of hatchling flatback turtles exposed to artificial light glow. Marine Ecology Progress Series 529, 279-288.
To assess the response of flatback hatchlings to common industrial light types a different intensities and elevation
At medium and high light intensities of all 3 light types (metal halide, fluorescent and high pressure sodium vapour) and at low intensity metal halide, hatchlings were more attracted to light at 2° elevation compared to 16° elevation. At low intensity there was no significant difference in orientation of hatchlings exposed to high pressure sodium or fluorescent light glow at either elevation.
Australian Government (Draft) National Light Pollution Guidelines for Wildlife including Marine Turtles, Seabirds and Migratory Shorebirds. Department of the Environmental and Energy, Canberra. 202 p
The purpose of these Guidelines is to raise awareness of the potential impacts of artificial light on wildlife and provide a framework for assessing and managing these impacts on susceptible listed wildlife.
The National Light Pollution Guidelines will raise awareness of the potential impacts of artificial light on wildlife and provide a framework for assessing and managing these impacts on susceptible listed wildlife. The Guidelines are built around a concept of best practice lighting design principles; and a risk assessed and adaptive management approach to light management near protected wildlife.