Using Aerial Photogrammetry to Map Distribution and Abundance of Green Turtle Nesting for Effective Conservation Planning 

Background

The green turtle population (Chelonia mydas) on the northern Great Barrier Reef is currently in decline. Raine Island, the largest remaining green turtle rookery, along with Moulter Cay, supports approximately 90% of the northern green turtle nesting population. However, research conducted over the last two decades suggests that Raine Island may not be producing enough hatchlings to sustain a viable population. While management strategies implemented through the Raine Island Recovery Project have helped to improve nesting success, concerns remain about the sustainability of the population. Therefore, it is critical to understand the broader spatial distribution and abundance of northern green turtle nesting outside of Raine Island in order to support effective conservation and management efforts for this species.

The aim of this project is to capture comprehensive data on the relative abundance and distribution of green turtle nesting in the northern Great Barrier Reef and Torres Strait. Over two seasons (2020/21, 2024/25), the project will conduct broad-scale aerial surveys of potential nesting beaches during peak nesting periods to:

1. Collect spatial data on the distribution, relative abundance, and density of green turtle nesting across the northern Great Barrier Reef and Torres Strait.
2. Identify sites with high nesting abundance or density, along with potential refugia (i.e. sites with suitable nesting habitat that are currently under utilised but could support nesting in the future).
3. Examine changes in the extent and distribution of green turtle nesting in comparison to previous records to assess any shifts in nesting patterns.
4. Capture data on the geomorphology of key nesting sites, which could impact the availability and suitability of nesting habitats. 

Surveys will be conducted using aerial photogrammetry, a technique that allows for large-scale, high-accuracy data collection with minimal observer error. Unlike traditional manned aerial surveys, this method permits detailed post-flight analysis, ensuring all nesting attempts are accurately recorded and species identification is refined. This method has proven effective in the past for monitoring turtle populations and nesting activities and is especially useful when surveying remote regions or when covering a large geographic area. 

Using Structure from Motion (SfM) photogrammetry techniques, surveys will also capture high-resolution morphometric data on nesting sites, including areas of sand, vegetation and beach rock. This, in turn, will be used to estimate the potential nesting area available for green turtles. Additionally, the creation of Digital Terrain Models will provide information on beach profiles and elevation which, if future surveys were to occur, could give insights into geomorphic changes over time, such as changes in island size, sand volume, and vegetation coverage.

Surveys will cover all potential nesting beaches north of Princess Charlotte Bay and in the Torres Strait and will be timed to coincide with peak nesting periods to ensure a representative sample of nesting effort for the population. This will allow for a more contemporary understanding of green turtle nesting patterns in the region, which has not been surveyed since 1999. 

Data gathered from aerial surveys will provide critical insights into the distribution, abundance, and density of green turtle nesting across the northern Great Barrier Reef and Torres Strait, along with how these nesting habitats may change over time. This, in turn, will help to inform future conservation and management strategies through the identification of key nesting sites and potential refugia under rising sea level predictions. Ultimately, the project aims to contribute to the long-term sustainability of the northern green turtle population by improving our understanding of their nesting dynamics and contributing to more effective and informed conservation strategies for this iconic species.

Collaborative Conservation Efforts for Green Turtles in the GBR and Torres Strait
 

Background

The Great Barrier Reef (GBR) is home to six species of marine turtle, with the region hosting critical nesting and foraging habitats for green, loggerhead, hawksbill, and flatback turtles. Marine turtles play vital ecological roles in seagrass dispersal, nutrient cycling and sediment production. They are also culturally significant to Traditional Owners and highly valued by local communities and visitors.

About 90 per cent of the northern Great Barrier Reef green turtle (Chelonia mydas) population nests on Raine Island, the world’s largest green turtle rookery, or on nearby Moulter Cay. However, nest monitoring has shown a 20-year decline in hatchling production, despite management efforts to improve reproductive success through the Raine Island Recovery Project. This suggests that Raine Island may not be producing sufficient green turtle hatchlings to sustain the population.

Habitat loss and rising sand temperatures due to climate change are the most immediate and broad-scale threats to green turtles. Hatchling sex is determined by temperatures experienced during incubation, with warmer nests linked to predominately female clutches. This phenomenon is known as ‘feminisation’ and is predicted to lead to a scarcity of adult males in the future, which could lead to reproductive failure and population collapse. Additionally, there have been reports of a decrease in the size of nesting turtles, increases in non-breeding periods, a lack of expected turtle numbers at feeding grounds and more frequent flooding of nests due to rising sea levels. Collectively, these reports indicate that the long-term sustainability of green turtle populations in the region is under threat, and there is a need to better understand the current population structure to predict what this stock may look like in the future.

This study aims to determine the abundance, structure and trajectory of the northern Great Barrier Reef green turtle population at selected foraging ground sites within the northern Great Barrier Reef and Torres Strait. Results from this study will help determine whether the recruitment of juvenile turtles to northern reefs is being impacted as a result of low hatchling production and feminisation of hatchlings at Raine Island. 

Surveys will be conducted using Capture-mark-recapture (CMR), a common method used to monitor marine turtle populations. Over three years, a representative sample of the northern Great Barrier Reef green turtle population at study sites in both the northern Great Barrier Reef and Torres Strait will be captured, tagged and released. Information will also be collected on size, sex and weight of turtles, and samples collected for diet and genetics analysis.

Fieldwork will be delivered in collaboration with First Nations communities within whose sea country this work takes place: the Kuuku Ya’u Traditional Owners and the Meriam Nation Traditional Owners of the eastern Torres Strait (Ugar, Mer and Erub). Through active participation in research and knowledge sharing, this project hopes to foster a collaborative approach to sustainable turtle conservation in the region.
 

Protecting Male Green Turtles: Essential Insights for Conservation in the Great Barrier Reef

Background

Green turtles are charismatic megafauna that have critical roles in the ecosystem, First Nations’ culture, and the economy. However, after decades of research and monitoring, serious concerns are now being raised regarding the sustainability of green turtles that breed in the northern Great Barrier Reef (northern Great Barrier Reef green turtles). Due to the warming climate and related environmental changes (e.g., sea level rise), hatchling production has declined massively since the 1996-97 breeding season. Hatched turtles, which are already reduced in number, are now mostly female at Raine Island, the major rookery for this population. This is due to a phenomenon known as ‘feminisation’, where sex ratios are skewed toward females when temperatures are warmer than average during nest incubation. As with many other species, marine turtles need males as well as females to reproduce, and so it is critical that male northern Great Barrier Reef green turtles are given comprehensive protection as a conservation priority.

A first step of conservation management is to understand where, when, and how animals use their habitats. For adult male turtles, key habitats are foraging and courtship areas, and migration corridors. Although some habitats are known by managers, many key habitats for northern Great Barrier Reef green turtles and how and when they use these habitats are yet to be identified. And while much is known about the migration and breeding patterns of adult female turtles, the spatial ecology of adult males remains poorly documented. Based on flipper tag recovery data and existing published reports, northern Great Barrier Reef green turtles are likely distributed over many thousands of km² where little information is available. Identifying the distribution and habitat use of adult male green turtles during courtship, migration and foraging, as well as understanding potential threats to these key habitats, is essential for effective conservation management of remaining males.

This project aims to examine the spatial and temporal distribution, as well as habitat use, of breeding adult male northern Great Barrier Reef green turtles during courtship and foraging periods and when migrating to and from these key habitats, along with any potential threats.

GPS satellite tracking tags will be used to gather crucial data on the movements and habitat use of adult male northern Great Barrier Reef green turtles. This technology offers high accuracy and global coverage, allowing researchers to track these turtles regardless of how far they move after tag deployment. Anecdotally, the major courtship areas for northern Great Barrier Reef green turtles are in the Torres Strait, with additional courtship activity observed near Raine Island. However, the abundance of courtship activity at Raine Island is insufficient to account for the vast number of adult females that nest there, implying that key courtship areas lie elsewhere. To address this, tags will be deployed just before or during the courtship period in early October, targeting adult males from the far northern GBR and Torres Strait, believed to be part of the northern Great Barrier Reef population. 

Fieldwork will be delivered in collaboration with First Nations communities within whose sea country this work takes place: the Kuuku Ya’u Traditional Owners and the Meriam Nation Traditional Owners of the eastern Torres Strait (Ugar, Mer and Erub).
 

Adapting to Climate Change: Protecting Turtle Populations from Heat Stress

Background

Four species of marine turtle breed within the Great Barrier Reef (GBR) region, including the endangered Pacific Loggerhead and Hawksbill turtle, as well as the Green Turtle and East Australian Flatback turtle, both of which are currently listed as ‘Vulnerable’ under the Queensland Nature Conservation Act. Climate change is threatening marine turtles, particularly in the far northern Great Barrier Reef, by increasing the temperature of nesting beaches, which reduces male hatchling numbers and leads to higher mortality rates among embryos and hatchlings due to heat stress. Optimal hatching occurs at temperatures between 26°C and 31°C, while temperatures above this range can reduce hatching success or skew the sex ratio towards females, a phenomenon known as ‘feminisation’. This is because like most reptiles, sex of marine turtle hatchlings is determined by nest temperatures during incubation: warmer nests produce mostly female hatchlings while cooler nests produce mostly male hatchlings.

Given growing evidence that climate change is reducing hatching success and leading to excessive feminisation in some northern marine turtle populations, including the northern Great Barrier Reef green turtle population, there is an urgent need to address the warming of nesting beaches, particularly in far north Queensland.

This project aims to explore large-scale methods for cooling turtle nesting beaches to temperatures that support high hatching success and balanced hatchling sex ratios. 

Artificial cooling trials will be conducted along nesting beaches near the Queensland Parks and Wildlife Service’s Mon Repos Research Facility on the southern Great Barrier Reef, which has the infrastructure to support both experimental trials and long-term nest monitoring. Three specific methods will be tested: artificial rain, artificial shade and natural shade from dune vegetation. Each approach will be assessed for its effectiveness in manipulating sand temperatures to achieve optimal incubation conditions across large areas of nesting beach and for large numbers of clutches. 
Although loggerhead turtles are the dominant species in this region, outcomes from these trials will be used to inform potential beach cooling strategies at northern Great Barrier Reef green turtle rookeries, helping to mitigate the impacts of climate change on northern green turtle populations.