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| "What does it say of mankind if we idly stand by and watch the extinction of a fellow species." |
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RECOMMENDATIONS FOR REDUCING THE IMPACT OF LIGHT POLLUTION PROBLEMS ON SEA TURTLE NESTING BEACHES.
There are many threats to marine turtle survival most of these have been well documented and in some cases management practices put in place to reduce these threats. At the present time there is little documentation available regarding the effects of light pollution on nesting and hatchling turtles on Australian beaches. As population increases and cities, towns and communities expand, development in beach areas has accelerated. This development may correspond to areas where turtles also nest, putting these turtles and hatchlings at risk by altering the natural habitat. The suggestions given in these recommendations are simple and not expensive to implement. The adoption of some or all of these recommendations would have a large impact in helping to preserve turtle nesting habitat.
The information contained in these recommendations has been collected from studies and papers that have been published from overseas sources. Because marine turtle nesting and hatching behaviour is common throughout the world it can be said that the information contained in these studies and publications should be relevant to marine turtles nesting and hatching in Australian waters. In other parts of the world there has been legislation put in place and local government laws adopted to combat the effects of light pollution on nesting and hatching turtles in areas of concern. At the present time no such laws exist in Australia and it is for this reason these recommendations are presented from our group.
The Mackay Turtle Watch Association would like to thank the following sources for the information included in these recommendations. The Florida Marine Research Institute. Blair E. Witherington. R. Erik Martin for the technical report “Understanding, Assessing and Resolving Light-Pollution Problems on Sea Turtle Nesting Beaches.” The web sites turtletime.org and seaturtle.org.
There are nine steps in nesting behaviours for adult female sea turtles. 1) Emerges from the surf zone. 2) Crawls up the beach to a point typically between the high tide line and the primary dune. 3) Prepares the nest site by pushing or digging surface sand away to form a body pit. 4) Digs an egg chamber within the body pit using the rear flippers. 5) Deposits eggs within the egg chamber. 6) Covers the eggs with sand. 7) Camouflages the nest site by casting sand principally with the front flippers. 8) Turns and heads toward the sea. 9) Crawls into the surf.
Nesting disruption
The most clearly demonstrated effect of artificial lighting on nesting is to deter turtles from emerging from the water. Elsewhere in the world research has reported dramatic reduction in nesting attempts by adult turtles on brightly lit beaches. Artificial light deterring turtles from nesting can be considered a form of habitat loss forcing turtles to choose less appropriate nesting sites or the potential to shed their eggs at sea..
Disruption of sea finding
After a sea turtle has camouflaged her nest, she must orient toward the sea and return there. Experiments have shown that turtles rely on vision to find the sea by balancing the light intensity within their field of view between their eyes. This balance guarantees orientation in the brightest direction. Many cases of misdirected sea turtles exist and adults have been found far from the ocean in parking areas and on roadways.
Hatching process
There are four main behaviours for hatchling sea turtles. 1) After hatching from an egg the hatchling will slowly move toward the surface and wait until the whole clutch has hatched. This generally takes one to seven days. 2) Hatchlings emerge from the nest in masse and orient toward the sea without delay. 3) Hachlings crawl in a frenzy, direct from the nest to the sea. 4) Hatchlings enter the sea and orient toward the vertical face of the waves and swim out to sea.
Disruption of sea finding
Sea turtle hatchlings rely on vision to find the sea by balancing the light intensity within their field of view between their eyes. This balance guarantees orientation in the brightest direction. After nest emergence artificial light has the potential to disorient and misdirect hatchling turtles away from the sea resulting in high mortality through exhaustion, dehydration and predators. Hatchlings, have been known to be lured into car parks and roadways and are often crushed by passing vehicles.
Misorientation of hatchlings after entering the water
There have been many instances recorded of hatchlings being lured back onto the beach by artificial lighting or attracted to artificially lit offshore developments. This exposes hatchlings to exhaustion and greater predator danger.
How Sea Turtles Perceive Light
Sea turtles and humans perceive light quite differently. Both the colour (wavelength) and relative brightness of light sources are important to the sea finding capabilities of sea turtles. Sea turtles are strongly attracted to light in the near ultraviolet to yellow region of the visible spectrum (short wavelength light.) This is not surprising considering they live in a medium, the ocean, that selectively filters out long wavelength colours.
Most light sources are composed of many wavelengths, each representing a different colour. Both humans and sea turtles are unable to distinguish among the spectral components; we see only one colour. However, because of spectral differences, the colour emitted by a particular light source may not appear the same to humans as to sea turtles. This can have important implications for effective light management. For example, a source emitting monochromatic (single wavelength) yellow light is unattractive or weakly attractive to sea turtles. Yet another source, which also appears yellow to humans but contains both red and green spectral components, can be highly attractive to sea turtles because of the green wavelength present. Consequently we cannot rely solely on colour when determining whether or not a light is likely to attract sea turtles.
Moon light
Questions frequently arise as to why a light source near a beach has any more influence over a sea turtles orientation than does a full moon. Although moon light may seem to be very bright to a human, its source is very distant. As light travels from the source to earth, it is scattered by the atmosphere and reflected off the ocean and features on land. As a result of these moderating influences, by the time moon light reaches the beach, it is only moderately directed. From a sea turtles perspective, one direction (the one towards an artificial light source) is often brighter and this will be the direction it will choose to orient itself.
It is a myth that the moons light affects hatchling emergence. Hatchling turtles do not emerge from nests according to the moons cycle.
SOLVING PROBLEMS CAUSED BY ARTIFICIAL LIGHTING
Artificial Light and Light Pollution
Not all artificial lighting should be considered light pollution. One person's environmental threat may be another person's safety and security. Light pollution may be considered as artificial light that is out of place. Examples of light pollution are: 1) Light sources that illuminate areas that require no security. This includes the beach itself. 2) Light sources that illuminate areas that are vacant or where there is no foot traffic. 3) Decorative lighting.
An artificial light source is likely to cause problems for sea turtles, if light from the source, can be seen by an observer standing anywhere on the nesting beach.
Managing Light Pollution
Any strategy to manage and reduce light pollution should begin with identifying problem light sources. This can be conducted by beach lighting inspections.
Minimizing The Effects Of Lighting From Indoor Sources
• Turn off lights that are not in use.
• Relocate moveable lamps away from windows that are visible from the beach.
• Tint windows that face the beach.
• Close opaque curtains or blinds after dark to cover windows visible from the beach.
Minimizing The Effects Of Outdoor Beach Lighting Sources
• Turn unnecessary lighting off or remove the light source.
• Reduce the wattage of problem lighting.
• Substitute light fixtures that are better focused so that light is concentrated only where it is needed.
• Shield light fixtures from the nesting beach.
• Recess light fixtures into roof soffits. This makes them more directional.
• Lower pole mounted light fixtures. Use louvered bollard type fixtures as a substitute.
• Reposition light fixtures to take advantage of natural light screens.
• Install timers to switch off lighting when no longer required.
• Install motion detection switches which only switch on when movement is detected and switch off again at a pre determined time.
• Replace conspicuous lighting on beach access ramps with hidden walkway only lighting. This lighting should be small light sources such as hidden light emitting diode type, which are excellent for this purpose.
• Governments and government agencies should administer a sound policy for safe guarding beach protection areas and dunal management.
• Plant native dune vegetation as a screen. This is most effective if planted near the crest of the dune closest to the beach.
• No fires or torches should be used on the beach after dark during sea turtle nesting season.
Alternative Light Sources
Where efforts to correct problem lighting has not been entirely effective additional strategies may be better suited. As previously discussed sea turtles are highly attracted to low wavelength light sources such as white mercury vapour Luminaires. The following is a list of alternative long wavelength substitutes . These light sources exclude short wavelength, Ultra violet, blue and green light properties . Although these lights will have a minimal effect on sea turtles they should be used with other light management techniques.
Low pressure sodium vapour lamps- While studies have shown that this is the least disruptive of commercially available lamps to some species of sea turtle it should be considered as a substitute for more disruptive lighting when there is no other choice.
Yellow Bug lights, Filters and Red LED's- Bug lights are tinted yellow to reduce the emission of insect attracting short wavelength light. These can be minimally disruptive to sea turtles but are considered inferior to low pressure sodium vapour lamps. Bug lights are available as either incandescent or a fluorescent tube type.
Amber or yellow filters installed in light fixtures vary in effectiveness and can fade. Yellow dichroic long pass filters are an exception and exclude short wavelength well and do not degrade.
Red light emitting diodes (LEDS) can be used for walkways and steps. The red light from LEDS remains a true narrow band red for the life of the lamp and is probably one of the light sources least visible to sea turtles. They also have the advantage of not degrading the night vision of people visiting the beach.
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