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Sea turtles and the environmental management of industrial activities in North West Western Australia

Pendoley, Kellie Lee (2005) Sea turtles and the environmental management of industrial activities in North West Western Australia. PhD thesis, Murdoch University.

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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.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Biological Sciences and Biotechnology
Supervisor(s): Bradley, Stuart
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