Sea
turtle hatchlings emerge from the nests at night and crawl
directly to the sea. They are able to locate the ocean from
the nest using visual cues. Orientating themselves away
from darker, landward silhouettes, hatchlings move toward
the open, lower, brighter seaward horizon. Once hatchlings
enter the sea, they swim offshore by orienting into surface
waves.
Hatchlings
also use a ‘magnetic compass’ to orient offshore
but before this is used it must be ‘calibrated,’
or set, by previous experience. Under laboratory conditions,
calibration is accomplished either by crawling in one direction
(toward a light source); or by swimming in one direction
either toward a light source or into surface waves.
Results
of recent scientific research indicate that to reach their
migratory goals, hatchlings must respond to specific cues
guiding their orientation from the nest to the sea, and
away from the beach.
The presence of artificial night lighting degrades the visual
environment at many nesting beaches, disrupting the ability
of hatchlings to either detect or respond to the cues required
for a crawl in the right direction. Research has also found
that even if these turtles ultimately locate the sea from
illuminated beaches, they usually swim more slowly and on
less direct paths. |
Instead of heading out to sea these
hatchlings in Florida were attracted by the lights of a
nearby apartment building. Photo: N Wu |
There
are 2 ways artificial lighting disrupts hatchling orientation
on the beach. The turtles may either crawl towards the
lights (‘misorientation’) or may be incapable
of crawling in any direction (‘disorientation’).
As a consequence, turtles may crawl for hours without
reaching the sea and become exhausted and dehydrated.
A prolonged beach crawl also increases their exposure
to predators that already scour the beaches for easy prey.
Each year tens of thousands of hatchlings die as a consequence
of disrupted orientation by artificial lighting. A disrupted
crawl might prevent the turtles from calibrating their
magnetic compass or result in miscalibration so that after
they enter the sea, they swim in inappropriate directions.
Mis-oriented
or disoriented hatchlings are sometimes found alive on
the beach, either late at night or the morning after failing
to locate the sea.
Source:
LORNE, Jacquelyn Kay and SALMON, Michael. Effects of exposure
to artificial lighting on orientation of hatchling sea
turtles on the beach and in the ocean. Endangered Species
Research, Vol. 3: 23-30, 2007
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