I walked 1,200km in the outback to track huge lizards. Here’s why

Sophie Cross, Author provided

Sophie Cross, Curtin University

In 2017 and 2018 I walked the equivalent of 28 marathons in the scorching Western Australian outback. Why, you ask? To assess how some of Australia’s largest lizard species interact with restored mines.

As part of my PhD research, I hiked in often extreme heat on a mine site in WA’s sparsely populated Mid West region. My fieldwork was both physically and mentally demanding, as I spent many hours each day walking through the bush looking for signs of monitor lizards.

Being in a remote location and mostly alone, I had plenty of time to ponder the wisdom of my career choice, particularly on days when temperatures exceeded 40℃ and not even the lizards ventured from their homes.

Pushing through these mental challenges was difficult at times, but my work has provided me with some of my most rewarding experiences. And what I discovered may be crucial for restoring habitats destroyed by mining.

Restoring abandoned mines

Habitat loss is a leading cause of biodiversity loss worldwide. Although mining typically has a smaller environmental footprint than other major industries such as agriculture or urbanisation, roughly 75% of active mines are on land with high conservation value.

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Read more:
Afterlife of the mine: lessons in how towns remake challenging sites

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There are around 60,000 abandoned mines in Australia, but very few of them have been officially closed. How to restore them is a growing public policy problem.

Sophie Cross walked more than 1,200km and tracked a young-adult perentie to find out whether they were using a restored mining area.
Author provided

Recovering biodiversity can be an exceptionally challenging task. Animals are vital to healthy ecosystems, yet little is understood about how animals respond to restored landscapes.

In particular, reptiles are often overlooked in assessments of restoration progress, despite playing key roles in Australian ecosystems.

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Read more:
What should we do with Australia’s 50,000 abandoned mines?

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Do animals return to restored habitats?

I wanted to know whether restored habitats properly support the return of animals, or whether animals are only using these areas opportunistically or, worse still, avoiding them completely.

To study how reptiles behave in restored mining areas, I hand-caught and tracked a young adult perentie. The perentie is Australia’s largest lizard species, growing to around 2.5m in length, and is an apex predator in arid parts of the country.

I tracked the lizard for three weeks to determine whether it was using the restored area, before the tracker fell off during mating.

The tracking device revealed how the perentie navigated a restored mine, before it fell off during mating.
Author provided

Previous methods of tracking assume the animal used all locations equally. But I used a new method that measures both the frequency with which animals visit particular places, and the amount of time they spend there. This provided a valuable opportunity to assess how effective restoration efforts have been in getting animals to return.

Restoration needs more work

My research, published this week in the Australian Journal of Zoology, shows that while the perentie did visit the restored mine, it was very selective about which areas it visited, and avoided some places entirely. The lizard went on short foraging trips in the restored mine area, but regularly returned to refuge areas such as hollow logs.

The method used GPS and a VHF tracking antenna to follow the perentie.
Author provided

This is because hot, open landscapes with minimal refuges present high risks for reptiles, which rely on an abundance of coverage to regulate their body temperature and to avoid predators. Such costs may make these areas unfavourable to reptiles and limit their return to restored landscapes.

In comparison, undisturbed vegetation supported longer foraging trips and slower movement, without the need to return to a refuge area. Unfortunately, areas undergoing restoration often require exceptionally long time-periods for vegetation to resemble the pre-disturbed landscape.

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Read more:
Why we’re not giving up the search for mainland Australia’s ‘first extinct lizard’

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How can we help reptiles move back into restored areas?

Restored landscapes often lack key resources necessary for the survival of reptiles. As vegetation can require a long time to reestablish, returning fauna refuges like hollow logs and fauna refuge piles (composed of mounds of sand, logs, and branches) could be crucial to aiding in the return of animal populations.

My research team and I have called for animals to be considered to a greater extent in assessments of restoration success. In the face of increasing rates of habitat destruction, we need to understand how animals respond to habitat change and restoration.

Failing to do so risks leaving a legacy of unsustainable ecosystems and a lack of biodiversity.

Sophie Cross, PhD candidate, Curtin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Huge restored reef aims to bring South Australia’s oysters back from the brink

Mud oysters played a largely unappreciated part in Australia’s history.
Cayne Layton, Author provided

Dominic McAfee, University of Adelaide and Sean Connell, University of Adelaide

The largest oyster reef restoration project outside the United States is underway in the coastal waters of Gulf St Vincent, near Ardrossan in South Australia. Construction began earlier this month. Some 18,000 tonnes of limestone and 7 million baby oysters are set to provide the initial foundations for a 20-hectare reef.

The A$4.2-million project will be built in two phases and should be complete by December 2018. The first phase is the 4-hectare trial currently being built by Primary Industries and Regions South Australia; the second phase will see the reef expand to 20 hectares, led by The Nature Conservancy.

Some of the 18,000 tonnes of limestone destined for the seafloor.
D. McAfee

Just 200 years ago the native mud oyster, Ostrea angasi, formed extensive reefs in the Gulf, along more than 1,500km of South Australia’s coastline. Today there are no substantial accumulations of mud oysters anywhere around mainland Australia, with just one healthy reef remaining in Tasmania.

This restoration project aims to pull our native mud oyster back from the brink of extinction in the wild, and restore a forgotten ecosystem that once teemed with marine life.

More than just seafood

Oysters played a large role in Australia’s colonial history. When European settlers first arrived they had to navigate a patchwork of oyster reefs (also called shellfish reefs) that filled the shallow waters of our temperate bays. These enormous structures could cover 10 hectares in a single patch, providing an easily exploited food resource for the struggling early settlers. Oyster shell was burned to produce lime, and the colony’s first buildings were built with the help of oyster cement.

Collectively, these pre-colonial oyster reefs would have rivalled the geographic extent of the Great Barrier Reef, covering thousands of kilometres of Australia’s eastern and southern coastlines.

The history goes back much further too. For thousands of years oyster reefs fed and fuelled trade among Aboriginal communities. Shell middens dating back 2,000 years attest to the cultural importance of oysters for coastal communities, who ate them in abundance and used their shells to fashion fishhooks and cutting tools.

Health oyster reef in Tasmania.
C. Gillies

The insatiable appetite of the newly settled Europeans for this bountiful resource was devastating. Not only were live oysters harvested for food, but the dead shell foundations that are critical for the settlement of new oysters were scraped from the seabed for lime burning. Armed with bottom-dredges a wave of exploitation spread across the coast, first overexploiting oyster reefs close to major urban centres and then further afield. The combination of the lost hard shell bed and increased sediment runoff from the rapidly altered coastal landscape saw oyster populations crash within a century of colonisation.

Today oyster populations are at less than 1% of their pre-colonial extent in Australia. This is not a unique story – globally it is estimated that 85% of oyster habitat has been lost in the past few centuries, making it one of the most exploited marine habitats in the world.

Today, across much of Australia’s east coast you will see Sydney rock oysters encrusting rocky shores, creating a thin veneer around the edge of our bays and estuaries. On the south coast you occasionally see a solitary mud oyster clinging to a jetty pylon. Many Australians don’t realise that this familiar sight represents a mere shadow of the incredible and largely forgotten ecosystems that oysters once supported.

Oysters are an unsung ecological superhero, with the capacity to increase marine biodiversity, clean coastal waters, enhance neighbouring seagrass, reduce coastal erosion, and even slow the rate of climate change. When oysters cement together, their aggregations form habitat for a great diversity of other invertebrates. A 25cm-square patch of oysters can host more than 1,000 individual invertebrates from a range of different biological groups, in turn providing a smorgasbord for fish.

Restoration site, formerly covered with dense oyster habitat.
D. McAfee

A solitary oyster can filter about 100 litres of water a day, which means that en masse they can function as the “kidneys” of our bays, filtering excess nutrients from the water and depositing them on the seafloor. In doing so, they encourage seagrass growth, while their physical structures help to dissipate wave energy and thus reduce the impact of storm surges.

As if all that weren’t enough, oysters are also a carbon sink, building calcium carbonate shells that are buried in the seafloor after death and eventually compacted to rock, thus helping to prevent carbon dioxide from cycling back into the atmosphere.

Building it back

Restoring oyster reefs has the potential to return these ecosystem services and increase the productivity of our coastal ecosystems. The Gulf of St Vincent project came about through an election promise by the South Australian Government to boost recreational fishing. A collaboration between The Nature Conservancy, Yorke Penninsula Council and the South Australian Government will deliver the reef’s foundations, while my colleagues and I at the University of Adelaide are working to ensure that the restored oysters survive and thrive, and that the reef continues to grow.

Hopefully this is just the beginning for large-scale oyster restoration in Australia, and the lessons learned from this project will guide more restoration projects to improve the health of our oceans. With other restoration projects also underway in Victoria and Western Australia, the tide is hopefully turning for our once numerous oysters.

Dominic McAfee, Postdoctoral researcher, marine ecology, University of Adelaide and Sean Connell, Professor, Ecology, University of Adelaide

This article was originally published on The Conversation. Read the original article.