Understanding the risk to flatback turtles (Natator depressus) from expanding industrial development in Western Australia

Whittock, Paul Abraham (2017) Understanding the risk to flatback turtles (Natator depressus) from expanding industrial development in Western Australia. PhD thesis, James Cook University.

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Abstract

An increased global demand for natural resources has driven a recent expansion in Western Australia's industry resource sector, notably within the North West Shelf (NWS) region. This demand has increased industry resource activities both offshore e.g. exploration, drilling, production, and nearshore of the NWS's coastal boundary e.g. dredging, construction, underwater blasting. Elsewhere, these activities are known to present a threat to marine turtles and there is a potential for the expanding NWS industry resource sector to present a threat and risk of impact to flatback turtles that are known to occur within the same region.

Threats posed to flatback turtles by developments and activities associated with the industry resource sector are managed through the Environmental Impact Assessment (EIA) process. The process includes two important phases: a screening/referral exercise that considers the potential presence of protected species within the development's footprint and determines the subsequent scale of the EIA; and an Environmental Scoping Document (ESD) which includes a risk-assessment process that helps inform the need and design of control measures required to remove or reduce the risk of impact to a species from a particular activity. To be effective, both phases require baseline species information and prior knowledge gained from follow-up case studies involving the species and a similar activity.

For flatback turtles and proposed industry resource sector developments/activities on the NWS, there are knowledge gaps that may prevent effective screening/referral and ESD phases, potentially resulting in an insufficient level of protection during construction or operation. This thesis has therefore been applied in nature to address these gaps and contribute information and knowledge that can be applied during the different EIA phases outlined above and ultimately to contribute to the conservation of flatback turtles within the region.

My first objective was to identify the baseline spatial movement and distribution of flatback turtles on the NWS and determine the extent of the industry resource sector threat by investigating their potential for interaction during different life phases. To achieve this objective, I used data from satellite tracking units that were attached to nesting flatback turtles at multiple rookeries on the NWS to investigate their movements and behaviour during their inter-nesting (Chapter 2) and subsequent post-nesting foraging (Chapter 3) life phases. I undertook a broad scale assessment of the potential likelihood for interaction and threat from the industry resource sector by identifying their overlap with areas that have the potential to host activities associated with the industry resource sector in the region.

I found differences between rookeries with regards to the extent of the threat from the industry resource sector. Flatback turtles tracked from offshore islands (Thevenard and Barrow) demonstrated the largest overlap of their inter-nesting home range and time with areas that have the potential to host industry resource sector activities. Extended inter-nesting movements from these offshore islands to the coastline close to the mainland also increased their exposure to current and planned major resource developments. I found no overlap of inter-nesting home range areas and time with areas that have the potential to host industry resource sector activities for turtles tracked from mainland rookeries (Mundabullangana and Port Hedland).

Following the completion of their inter-nesting phase, I further investigated their movements, behaviour and likelihood of interaction with the industry resource sector during their foraging life phase (Chapter 3). I found that foraging areas were broadly dispersed across the region, with the furthest foraging area situated 2511 km from the original nesting site (Port Hedland) within the Gulf of Carpentaria in Queensland state waters. I delineated five main areas of concentrated foraging use. I recorded an overlap of habitat use by flatback turtles from multiple rookeries within the same RMU for the first time, with some individual foraging areas utilised by flatback turtles tracked from rookeries of different origin.

I considered that during the flatback turtle foraging life phase, the extent of the threat from the industry resource sector was lower compared to their inter-nesting life phase. Nearly half of their foraging areas were situated within an existing protected area and there was a smaller overlap of their home range areas with petroleum title areas when foraging. Their behaviour appeared more flexible when foraging compared to inter-nesting, showing low site fidelity and moving between multiple areas distributed across a broad area.

My second objective involved investigating the environmental variables that influenced flatback turtle distribution during their inter-nesting life phase and generating a habitat suitability model to identify areas of the NWS where flatback turtles may be present and specific areas where they have the highest likelihood of impact from industry resource sector activities.

I used an ensemble ecological niche-modelling approach to identify the environmental variables that influenced inter-nesting flatback turtle distribution across the NWS study area (Chapter 4). Inputs into the model included selected environmental variables and flatback turtle presence data based on inter-nesting tracking positions from multiple rookeries in the region. Outputs of the model included the importance of each variable and a regional flatback turtle inter-nesting habitat suitability map. I compared the inter-nesting habitat suitability map with a cumulative resource sector impact layer to produce a regional risk map and identify specific inter-nesting areas with the highest likelihood of interaction across the region.

I found the primary environmental variables that influenced flatback turtle inter-nesting distribution were bathymetry, distance from coastline and sea surface temperature. The habitat suitability map demonstrated areas of inter-nesting habitat in close proximity to many known flatback turtle rookeries across the region. I found areas of suitable inter-nesting habitat overlapped spatially with resource sector impact areas in close proximity to nearly all known flatback rookeries within the NWS study area, with notable overlaps of highly suitable habitat with areas of high cumulative impact in areas offshore from the Gorgon Liquefied Natural Gas (LNG) development at Barrow Island and the existing port at Port Hedland.

My third objective was to contribute an EIA follow-up case study by evaluating the predicted vs. actual consequence of the Gorgon LNG dredging operation at Barrow Island to inter-nesting flatback turtles. I also considered the suitability of implemented control measures by comparing flatback turtle movement and behaviour at different phases of the dredging operation and combining this with actual survivorship data as represented by injury/mortality observations recorded by onboard Marine Fauna Observers (MFOs).

To achieve this objective, I attached satellite tracking units and time-depth recorders to nesting flatback turtles at different phases of the Gorgon LNG dredging operation: before (baseline), during (dredging) and after (post-dredging). I compared specific inter-nesting movement and behavioural characteristics recorded during each of these dredging phases and reviewed the observation records of onboard MFOs.

I found that during the active dredging operation, flatback turtles had a substantially higher use of the dredging areas compared to the baseline and post-dredging phases (Chapter 5). During the dredging operation, they used the areas being dredged to undertake longer and deeper dives compared to baseline and post-dredging phases, utilising the now deeper and highly turbid waters of the dredging areas. Despite their increase in time spent within the active dredging areas and subsequent increase in potential exposure to entrainment or vessel strike, no events of injury or mortality were detected by the onboard MFOs.

I considered that the implemented control measures may have been effective in preventing their injury or mortality, however, based on the results showing that turtles remained within the active dredging areas, the spatial scale of the control measures' effectiveness in deterring turtles from the area may be smaller and less effective than first anticipated. I further reviewed the potential drivers behind their increased use of the dredging areas during the active dredging operation. The most likely driver was considered to be a combination of the increase in turbidity and acoustic noise within the dredging area; potentially resulting in an area that was predator-free and reduced the likelihood of predator detection.

This thesis demonstrates that the expanding industry resource sector provides a risk of impact to NWS flatback turtles when inter-nesting and foraging offshore, though any realised impact from this threat is likely dependent on the scale that it is assessed at. At a project-by-project scale, the potential for an individual development or activity to provide a population wide impact to flatback turtles situated offshore is limited due to the existing regulated EIA process and variations in flatback turtle spatio-temporal movement and behaviour characteristics demonstrated at multiple rookeries in this study. However, at a regional scale, the movement and behaviour characteristics, spatial extent of the industry resource sector and limitations within the EIA process for assessing cumulative impact, provides potential for population wide impacts to NWS flatback turtle rookeries from the industry resource sector.

Item ID: 48875
Item Type: Thesis (PhD)
Keywords: Australia, conservation and management, dredging, EIA, environmental impact Assessment, flatback, foraging, habitat degredation, habitat suitability models, home range, industrial development, industry resource sector, industry, inter-nesting, marine protected areas, mining industry, Natator depressus, noise, North West Shelf, satellite tracking, Western Australia
Additional Information:

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Whittock, Paul A., Pendoley, Kellie L., and Hamann, Mark (2014) Inter-nesting distribution of flatback turtles Natator depressus and industrial development in Western Australia. Endangered Species Research, 26 (1). pp. 25-38.

Chapter 3: Whittock, Paul A., Pendoley, Kellie L., and Hamann, Mark (2016) Flexible foraging: post-nesting flatback turtles on the Australian continental shelf. Journal of Experimental Marine Biology and Ecology, 477. pp. 112-119.

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Date Deposited: 10 May 2017 01:22
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 50%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050211 Wildlife and Habitat Management @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960809 Mining Flora, Fauna and Biodiversity @ 50%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 50%
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