Blair
Witherington Comments…
The
issue of reducing disturbance to sea turtles on the nesting
beach is not a simple as choosing a light that does not
affect sea turtles (which can be any light that happens
to be turned off). Lurking about on a beach can disturb
nesting turtles, lights or no lights. Some nesting sea turtles
are more sensitive to this "human presence" than
are others.
For instance, green turtles and loggerheads that have just
emerged from the sea nearly always respond to a human approaching
within the turtle's field of view by withdrawing their necks,
pivoting, and returning to the sea, whereas olive ridleys
are known to complete their nesting even after being plucked
from the sea as they emerge, carried up the beach, set in
the sand, and watched intently by an audience of egg collectors
(please do not try this at home). |
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Most
sea turtle researchers quickly come to know how closely
they can approach the turtles that nest on their beach
but may wonder if the use of light by workers on the
beach may frighten turtles they cannot see. It has been
noted that lighting on the beach will keep loggerheads
and green turtles from emerging to nest, but once these
turtles emerge to nest, a moving person without a light
is more likely to cause nesting abandonment than a motionless
person with a light.
Although lights that cause nesting turtles to abandon
nesting attempts are bad, lights that cause hatchlings
to move in the wrong direction and die are probably
worse. Generally, the longer a light is left on the
greater the harm it can cause hatchlings (the longer
they may travel in the wrong direction).
So how can one travel, work, and see one's way on a
sea turtle nesting beach while minimizing harm to sea
turtles? I have the following tips (generally supported
by evidence but open for debate).
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Use
light sources that are pure red and use them only
briefly. Pure red light (light that is composed mostly
of wavelengths in the red region of the visible spectrum)
is preferred for two reasons. The first is that sea
turtles apparently do not see red light as well as
we do. The second reason is that red light does not
bleach the photopigment we depend upon for our night
vision. Consequently, one can use a red light briefly
to fill out a data form and still be able to see in
the dark when the light is turned off. Not all reds
are the same. Some are more pink (whiter than red)
to begin with and some start out red but fade to purple
(blue and red) over time. One of the most pure and
fade resistant red filters I have found is the red
plastic (lexan) of automobile tail lights (the lens
can be cut to flashlight-size with a coping saw and
the entire light fixture can be mounted on an ATV).
In the USA, some makers of small flashlights offer
a red lens that also is very good. I have also seen
small lights with tiny red LED (light emitting diode)
lamps that are very very good (these are often termed
map-reading lights). Most red films of acetate that
one might use to cover a flashlight fade quickly and
because of this are not very good. Red tape is fair
in a pinch but it diffuses the light too much to focus
it well.
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Don't
fear the dark. Most people are surprised by how well
they can see at night without artificial lighting.
After about twenty minutes in the dark (or under a
red light) the human eye can see well enough to keep
its owner from tripping on even the darkest of nights.
If the moon is out, one may even read a wristwatch.
Eat carrots. Losing a dependence on artificial light
will allow one to see well beyond the flashlight beam.
Believe it or not, one can generally see the silhouette
of a turtle at a greater distance without a flashlight.
Source:
Blair Witherington, Florida Marine Research Institute:
Tequesta Field Laboratory
19100 Southeast Federal Highway, Tequesta, Florida 33469
USA E-Mail: spinnaker@prodigy.ne ; Phone: 561-575-5408;
FAX: 561-743-6228
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