The nesting demographics of sea turtles using beaches within the Barrow, Lowendal,
Montebello (B-L-M) island complex on the North West Shelf of Western Australia were
examined in the context of their spatial and temporal distribution and potential for
exposure to industrially based artificial light sources. The distribution of overnight turtle
tracks throughout the island complex confirmed high density nesting of Chelonia mydas
(green turtles) on deep, sandy and high energy beaches and Natator depressus
(flatback turtles) on deep, sandy and low energy beaches, while Eretmochelys
imbricata (hawksbill turtle) tracks were most visible on shallow, sandy beaches
adjacent to near shore coral reef habitat. The three species exhibited a summer
nesting peak. Hawksbill turtles commenced nesting in September and continued
through to January, green turtles commenced in November and decreased in March.
Flatback turtles displayed the most constrained nesting season reported to date in
Australia with 86% of the animals visits recorded in December and January only.
Nesting population sizes estimated for the three species suggest that on a national
scale the B-L-M complex is a moderately large green turtle and a large flatback rookery
site. The hawksbill rookery is large on an international scale. While none of the green
turtle nesting beaches fell within a 1.5 km radius of industrially based artificial light
sources an estimated 42% of nesting flatback turtles and 12% of nesting hawksbill
turtles were potentially exposed to these light sources.
Testing of green turtle and hawksbill hatchling response to different wavelengths of
light indicate that hatchlings from the B-L-M region respond to low wavelength much
like hatchlings tested in North America (Witherington 1992a). Flatback hatchlings
displayed a similar preference for low wavelength light however their responses to
discrete light wavelengths between 400 nm and 700 nm suggest that this species may
not discriminate well between wavelengths that lie between 450 nm and 550 nm. This
response may be related to the rapid attenuation of visible light that occurs in the turbid
near shore habitats favoured by this species.
Field based arena studies carried out to investigate hatchling behaviour on nesting
beaches with light types commonly used in industrial settings found green turtle and
flatback hatchlings are significantly attracted to these lights compared to controls.
Lights that emit strongly in the low wavelength range (i.e. metal halide and fluorescent)
caused hatchling misorientation at lower intensities than the test light that emitted
relatively poorly in this range (high pressure sodium vapour). Hawksbill hatchlings
tested in situ under the influence of actual oil and gas onshore and offshore facility
based lighting were disrupted from the most direct line to the ocean by these light
emissions. Emergence fan mapping methods that measure hatchling orientation on
nesting beaches were refined and are proposed as an alternative monitoring tool for
use on beaches that are logistically difficult to access for large scale experimental
orientation studies. The hatchling behaviour was clearly complicated by beach
topography and moon phase.
Satellite tracking of post nesting female green and hawksbill turtles from North West
Shelf rookeries has identified the Western Australian location of migratory corridors and
foraging grounds for these species while Scott Reef turtles migrate from their south
Timor Sea rookery to Northern Territory waters. Green turtle nesting on Barrow Island
and Sandy Island (Scott Reef) forage at feeding grounds 200 1000 km from their
nesting beaches. Hawksbill turtles nesting at Varanus Island and Rosemary Islands
forage at locations 50 450 km from their nesting beaches. While all of the nesting
beaches within the B-L-M island complex are protected under the Barrow-Montebello
Marine Conservation Reserves, the only foraging ground similarly protected is the
Northern Territory foraging ground used by Scott Reef green turtles. None of the
foraging grounds used by North West Shelf green or hawksbill turtles is currently
protected by conservation reserves.
| Identifer | oai:union.ndltd.org:ADTP/221722 |
| Date | January 2005 |
| Creators | Pendoley@newton.dialix.com.au, Kellie Lee Pendoley |
| Publisher | Murdoch University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.murdoch.edu.au/goto/CopyrightNotice, Copyright Kellie Lee Pendoley |
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