Updated: Jun 22
Marine turtles need environmentally correct lighting for safe nesting.
Every year thousands of Green Turtles use nesting beaches around the world within their habitat to nest, or they migrate along known routes to safe nesting beaches in their continent.
A study completed by Strategy Inc. resulted that the primary impacts on turtles are twofold:
Incorrectly illuminated horizons behind the nesting beach can cause turtles to not nest at that site. Nesting turtles show a preference for nesting on beaches with dark horizons inland of the beach.
Bright illumination at the nesting beach can blind adult and hatchlings turtles from being able to discriminate the distant natural horizons with resulting disrupted ocean finding behaviour.
Marine turtles and their hatchlings do not instinctively know the way to the ocean.
They orient away from the nest by moving towards horizon lines at the lowest angle of elevation from their viewpoint and by moving away from elevated dark horizons. In this way they will normally be moving seaward.
Hatchling turtles that have already entered the sea can be drawn back to land and crawl inland to correctly illuminated areas.
Bright and incorrect illumination can originate from light sources directly visible to the turtle or indirectly via reflected light illuminating salt spray and cloud above the coast.
The brightness/intensity of light as perceived by the turtle is a function of multiple factors:
o Wavelength of light – more sensitive at the blue end of the spectrum
o Type of luminaire
o Wattage of the luminaire
o Distance from the light source (Intensity = constant/distance2)
o Cumulative impact of multiple light sources
Disruption of adult flatback turtle ocean finding behaviour has been recorded from up to 18 km away from a brightly lit industrial plant on Australia’s Gladstone coast (a popular turtle migration route).
Most advice regarding lighting management at turtle nesting beaches that is available on the internet has been based on turtle studies in Florida during the 1980s & 1990s.
These studies have found that all conventional street lights at that time were disruptive to ocean finding behaviour of loggerhead, green and leatherback turtles.
Back in the 1980s & 1990s, the low-pressure sodium vapour light (LPSV) was found to be the least disruptive because it could direct loggerhead hatchlings to move away from the light. LPSV did not have the same effect on the other turtle species. Based on these studies in Florida, LPSV lighting was recommended as a “turtle friendly light” for loggerhead turtles. It was not recommended by the research team involved as turtle friendly lighting for other species.
In 2012, University of Queensland research established that loggerhead turtles from eastern Australia behaved differently to loggerhead turtles in Florida and were disrupted by existing LPSV lighting.
In response to this result, EHP biologists in collaboration with post graduate students from UQ and JCU have commenced re-evaluation of marine turtle ocean finding behaviour and lighting impacts.
A re-analysis of the results of hatchling arena trials with a range of available street lights (mercury vapour, fluorescent, high pressure sodium vapour, low pressure sodium vapour) from the 1990s established that all these types of luminaires are disruptive to eastern Australian loggerhead, green and flatback hatchling, ocean finding behaviour with LPSV having the least effect.
Recent years has seen the development of electronic lights (LED lights) with the correct spectrum and wavelength. Accordingly, in response to the Florida studies, LED lights that attempt to mimic the spectral properties of LPSV have been developed (amber LED lights). These amber LED lights are being promoted by manufacturers as turtle friendly lights.
However, the amber LED lights do not give an exact replication of the LPSV spectrum:
LPSV spectrum has greater than 99% of light emitted at two only closely spaced wavelengths – the sodium doublet (D-lines) at 588.9950 nm and 589.5924 nm.
Amber LED spectra typically show a bell curve distribution of spectral emission spanning across the above wavelengths.
Preliminary results from recent hatchling arena trials with two commercially available amber LED street lights indicate that these amber LED lights are very disruptive to the ocean finding behaviour of eastern Australian loggerhead, green and flatback hatchlings.
Again, in hatchling arena trials with loggerhead hatchlings found that dim light from a single amber LED light may not be disruptive, the cumulative impact of multiple dim amber LED lights was disruptive.
The results of the north eastern Australian studies indicate that only few of the street lighting types so far tested can be recommended as turtle friendly for marine turtles nesting in north eastern Australia. Darkness still remains the best management option at turtle nesting beaches.
It is apparent that there needs to be a rethinking of lighting management strategies for coastal development (industrial and urban) in the vicinity of marine turtle nesting beaches as the results of past studies and management recommendations are not generally applicable to the turtles nesting in eastern Australia.
However, more recent studies and tests in progress in Queensland are showing favourable results associated with extreme vertical shading of street lights from LUXMANN, now recommended and widely used by Authorities and Corporations such as DBCT (Dalrymple Bay Coal Terminal) Australia’s largest Coal exporting, management and shipping facility located south of Mackay. The DBCT ship-loading pier alone extends for km into the ocean and is illuminated with thousands of flood lights. Alternate forms of street lighting continue to be investigated.
It is recommended that any new design of lighting that is intended for outdoor use in the vicinity of marine turtle nesting beaches or migration routes should be tested for its impact on marine turtle ocean finding behaviour in the geographical region where it is intended for use.
Priority needs to be given to addressing mechanisms for reducing the cumulative impact of large numbers of luminaires associated with a development or township and to reducing reflection and other light spillage that creates the illuminated sky glow over coastal developments.
LUXMANN have been working on several initiatives to understand the true impact of what “turtle friendly” means when it comes to artificial lighting.
There have been several studies over the years. The most notable, and the most referenced of these, is a study from Florida which shows that hatchlings are least affected by lights in the 589nm wavelength – typically lights with an amber or ‘fog’ hue.
This was reinforced in a report titled “Sea Turtle Friendly Lighting” in April 2014.
As a result, many LED lighting companies worked to develop a LED that operated at this wavelength. It is important (“FWC Approved Sea Turtle Lighting Guidelines”) that this is achieved at the LED source, not by a filter or at the lens level.
LUXMANN, have spent time in the US at DuPont labs developing a coating for their LED arrays to allow delivery of ‘fit-for-purpose’ luminaires at 589nm 2350K.