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2nd ASEAN Symposium
and Workshop on
Sea Turtle Biology and Conservation
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SESSION
3: Beyond the Beach....
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ABSTRACTS
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Nearshore
Turtle Hatchling Distribution and Predation
Nicolas J. Pitcher, Simon Enderby, Thomas Stringell, Lynne Bateman
Hatchling
green turtles (Chelonia mydas) emerge from their nests at night and crawl over
the beach to the sea using light as the primary cue for seafinding. Once they
enter the sea they are usually guided by wave and magnetic cues and head
straight off shore. Predation rates decrease as hatchlings distance themselves
from their natal nests.
In Sabah the
turtles' open sea finding mechanism must be altered slightly to account for the
numerous small islands and reefs that prevent a clear off shore migration, and
hatchlings face higher rates of predation than elsewhere in the world..To test
nearshore orientation and rates of predation, hatchlings were fitted with
harnesses and lighted floats and were followed as they left the natal beach.
Swim speed and off shore headings were determined from repeated position data
gathered by DGPS and triangulation, and predation rate and location were
notedfor each trial.
Hatchlings
suffered 40-60 % mortality within the first two hours at sea, the majority
before they crossed the 10 m depth contour. Once hatchlings made it past the
reef and into deeper water predation rates dropped by two thirds. Hatchlings
were found to orient in the nearshore in the absence of waves, and to turn
toward the open sea long after leaving the beach, after picking up orientation
cues from waves and currents. |
