Parks Australia science news Edition 8 — July 2020

Welcome to the 8th edition of the Parks Australia science news. In this edition we take a second trip to Ashmore Reef and share results from the first voyage. We also check in on Booderee’s eastern quolls, get an update on the Christmas Island blue-tailed skink translocation, and see how Kakadu has made use of the recent lockdown to undertake an opportune survey.

Field highlights from Ashmore Reef

In July last year, we took you to the heart of the Timor Sea, tracking the adventures of an intrepid team of scientists that spent two weeks surveying the islands of Ashmore Reef Marine Park. These tiny dots in the middle of the ocean are a magnet for seabirds, turtles and shorebirds, some of which travel many hundreds of miles to eat, rest and breed.

Learn more about the vegetation, bird and invasive species surveys the team completed during the first half of the Ashmore Environmental Assessment Project by reading Ashmore Reef Marine Park: An Indian Ocean Oasis which was published in 4th edition of the Parks Australia Science Newsletter. If you’re short on time, you can just watch the short video below. Ashmore Reef Marine Park: an isolated sanctuary

Ashmore Environmental Assessment Project

The project set out to see how life is fairing at Ashmore Reef and what management steps will be needed to address threats to this ecosystem. In this article, we’ll share some field highlights from the second half of the project and overall project results.

In mid-2019, a different team of scientists from institutes across Australia, including CSIRO and the University of Western Australia, gathered in Broome for the 30-hour trip to the marine park. Their mission was to assess the health of the reefs and seagrass beds that surround the islands and survey the marine species that call these habitats home. Globally, Ashmore Reef is known for its internationally significant populations of birds: 15 seabird and four heron species have been observed breeding on the islands, many other seabird species roost there and a further 30 species of migratory shorebird stop over on their journey along the East Asian-Australasian Flyway.

However, under the waves, Ashmore’s biodiversity truly comes to the fore: 275 species of coral and over 750 species of fish have been recorded here, along with many, many more invertebrate species. Notably this list includes 47 species of sea cucumber, 178 species of echinoderms (e.g., sea stars and urchins) and 433 molluscs. This diversity is significantly higher than nearby reefs. Green, hawksbill and loggerhead turtles breed and feed here, and the West Island lagoon is home to a small dugong population. Historically, Ashmore was a recognised global hotspot for sea snakes but populations started to decline in the early 2000s and in recent years, only a handful of animals have been sighted.

Assessing the health of such a diverse marine ecosystem is challenging, with many different components to consider. The team focused on completing comprehensive surveys of the coral reef communities, with a specific focus on trochus, giant clams, sea cucumbers, sea snakes, fish and sharks. They also assessed benthic cover of coral, macroalgae and seagrass, and took a closer look at the biomass and productivity of the seagrass beds. The principal survey method used followed a globally standardised Underwater Visual Census approach; however, a very important aspect of this project was trialling innovative technologies and survey techniques.

Like many of the Australian Marine Parks, Ashmore Reef Marine Park is remote. Typically, this means that conducting science is expensive and opportunities are few and far between, so we’re always looking for ways to improve our research efficiency. On this trip, CSIRO scientists trialled the environmental DNA (eDNA) approach to monitor marine biodiversity, filtering approximately 700 kilograms of seawater from 110 sites around Ashmore Reef. The method involves sieving tiny genetic remnants from seawater samples and comparing their unique “fingerprints” against databases to identify species. While still relatively new, the eDNA approach promises enormous benefits, from detecting species that like to stay hidden to vastly reducing the time it takes to complete biodiversity surveys.

Zebra shark on Ashmore Reef. Image credit: Ru Somaweera.

What has the project told us?

The Ashmore Reef voyages might be a distant, tropical memory for the project team, but the work hasn’t stopped. In the intervening months, they’ve been processing and analysing the huge amounts of data (more than 50,000 observations) collected. The results are now in, and overall they reinforce the message that Ashmore Reef is an ecosystem worth taking great care of.

The status and diversity of seabirds and shorebirds appears healthy, with an increase in the number of adults observed across several species since at least 2014. There has also been an expansion in breeding territory for a handful of species including the lesser frigatebird, brown and red-footed booby, sooty tern and brown noddy. For the first two species, the data indicates that ≥1% of their global population depends on Ashmore Reef, adding further weight to the marine park’s Ramsar listing.

Introduced species, known to occur on Ashmore’s islands were also assessed. The invasive tropical fire ant, believed to have been introduced in the 1990s, showed evidence of recovery from an earlier pilot control project and was found on all three islands. Encouragingly, despite targeted searching, no clear evidence of interference with nesting seabirds or turtle eggs was observed. Based on the impacts tropical fire ants have had elsewhere, these findings suggest we need to clarify what is happening on Ashmore’s islands before we settle on the best management strategy.

Asian house geckos and a number of weed species, particularly buffel grass, were also the subject of targeted surveys. Geckos were found in abundance on native octopus bushes (Heliotropium foertherianum) on West Island but further research will be needed to determine if their presence is having an impact, for example on invertebrate communities. The hardy, fast-growing buffel grass, as well as a number of other threatening weeds, were found to be well established on West Island. The presence of these weeds is a cause for concern because they can out-compete native species. At Ashmore, this could potentially have important ramifications for the seabirds that rely on this vegetation for nesting sites.

Below the waves, eyes were peeled for marine species of concern like the crown-of-thorns starfish. A single individual was observed but no widespread evidence of damage. Across the reef flats, the corals were in good condition and species diversity is high, with signs that recovery from historical coral bleaching events is well underway. Coral cover varied across the reef, with reef edges showing the highest density, dominated by Acropora, Pocillopora, Porites and favid species. The continued health of the reefs here will depend, in part, on the frequency and strength of future coral bleaching events.

The seagrass beds, important feeding grounds for resident turtles and nursery habitats for a range of species, were also found to be healthy. While shoot density was not high and fewer species were observed from previous studies, the beds were extensive and very productive. Observed fish assemblages were highly diverse, with a total of 22,121 finfish from 43 families recorded. Sharks were rarer and while there are other studies that suggest numbers have rebounded since the cessation of fishing, this work suggests that populations may still be depressed.

Unfortunately, populations of exploited sea cucumbers, clams and trochus continue to suffer the effects of historical harvesting. The abundance of many species remains extremely low, and some species are thought to have reproductively ineffective populations, suggesting they may never recover. Further surveys to confirm this are required. Sea snake numbers also continue to be very low at Ashmore, with the team spotting a single olive sea snake from the diving tender after two voyages and extensive survey efforts. The mystery surrounding the disappearance of sea snakes from Ashmore Reef continues, with a number of theories being the focus of continued research.

Where to next?

This integrated terrestrial-marine project is the first of its kind at Ashmore Reef Marine Park. It has provided data which will help us consolidate our baseline understanding of the marine park’s terrestrial and shallow water ecosystems. It has also provided data that will add to historical data sets, providing insights on how species, communities and habitats have changed over time. Together, this information helps us assess priority management needs for this remote ocean oasis. Parks Australia will continue to work with the science community in ensuring Ashmore Reef Marine Park is protected for the benefit of all Australians.

A bale of turtles gather in the sheltered waters of Ashmore Reef. Image credit: Tommaso Jucker, CSIRO. Indigenous rangers check on Booderee quolls

Earlier this month Booderee National Park Indigenous rangers were out trapping the park’s eastern quolls (Dasyurus viverrinus) to conduct health checks and to look for any pouch young. Three females were captured and two had 10mm-long pouch young; four in one female’s pouch and three in the other. The third is likely to have pouch young the next time we catch her as she was spotted frolicking with a male a few weeks ago, and the gestation period is 21 days. These quolls are part of an effort to re-establish a wild population of this species in Booderee National Park, with two translocations into the park undertaken in 2018 and 2019.

These translocation have been successful in meeting a number of milestones, including: the ability of the quolls to survive in the wild after being raised in captivity, with some individuals monitored in the park for over two years; and the ability not only to survive but also to breed successfully in the wild. In addition to this is the good news that their habitat in Booderee was not impacted by the summer bushfires.

We have also learned a great deal from these first two translocations, and these lessons are informing management and plans for future translocations. High mortality shortly after release has been attributed to loss of condition after the shock of release from captivity, combined with naivety making them more susceptible to predation by foxes, dogs and pythons. However, monitoring has revealed that if released quolls can survive for around eight weeks then they typically survive for far longer. Therefore, in order to boost the survival of captive bred quolls during this early period, we plan to release the quolls into a 400ha predator-free sanctuary enclosure for a few months prior to their move to Booderee. We believe this will significantly increase survivability as the quolls will have time to learn how to find food and shelter more effectively.

One milestone this project is yet to meet is confirmation of young surviving through to breeding age. As the fate of young from the past two breeding seasons remains uncertain, this year we plan to place tail-mounted radio tracking devices on the joeys as they are weaned so that we can monitor their movements. The recent pouch checks have informed us which individuals have young and how advanced they are, allowing us to plan for radio tracking work to occur in October/November. We are hoping that this will answer the question of whether they are succumbing to predation, or dispersing out of the park.

This project is a collaboration between Parks Australia, the Australian National University, Rewilding Australia, Taronga Conservation Society and WWF Australia, with support from Wreck Bay Aboriginal Community Council.

Image left: Pouch young. Image right: Park staff weighing a quoll. Image credit: Rewilding Australia. Bruce the quoll's hind foot. While the other five quoll species have five toes, the eastern quoll has only four, missing a halux (big toe).

Blue-tailed skink update

On National Threatened Species Day last year (7 September 2019), 300 blue-tailed skinks (Cryptoblephaurus egeriae), extinct in the wild in their home range of Christmas Island, were released as part of a Conservation Introduction on the tiny, 2.08ha island Pulu Blan, part of the Cocos (Keeling) atoll. This release, designed to augment a successful captive breeding program, has been highly successful with the population on Pulu Blan already increasing through natural recruitment.

Following this success, a second release of 300 skinks was attempted on neighbouring Pulu Blan Madar (1.78ha) in March 2020. However, the skinks released on this island immediately encountered problems. Undetected during a survey of the island in February 2020, a high-density colony of invasive yellow crazy ants (Anoplolepis gracilipes) began impacting the animals, causing scarring to their tails and pushing them to the edges of the island.

In a bid to save this new release of skinks, Christmas Island National Park staff began looking for ways to remove yellow crazy ants (YCA) from the island.

A fipronil based paste-like ant bait, Vanquish ProTM has been found to be highly effective in the control of YCA on Christmas Island. However, its non-target impact on vertebrates such as reptiles is unknown. Park staff developed a baiting strategy using small sample vials with 4mm holes drilled in them as bait stations attached to vegetation, to prevent non-target animals accessing the bait. Trials also indicated that reptiles were unaffected by secondary poisoning (eating insects that had consumed Vanquish ProTM).

On the 17 June, park staff deployed over 1000 bait stations containing over 5kg of Vanquish ProTM across the island with dramatic effect. In less than 24 hours ant numbers had declined dramatically and are now only present at 17 of 100 monitoring locations on the island. Further monitoring will establish if the blue-tailed skink population recovers following the baiting. We wish them well! Image left: Yellow crazy ants accessing Vanquish Pro™ from a deployed bait station. Image right: A blue-tailed skink investigates his new home on Pulu Blan Madar. Lockdown provides survey opportunities in Kakadu

Kakadu staff have used the recent COVID-19 lockdown as a rare opportunity to collect baseline data on the impacts of vehicle traffic on wildlife in Kakadu National Park. Collisions between vehicles and animals are a significant cause of animal mortality within the park and dead animals on or by the side of the road (roadkill) are frequently seen throughout the park. While the park was closed to outside visitors to reduce the risk of the virus spreading to communities, the only vehicle movements in this traditionally high visitor season were of locals and essential services. With traffic significantly lower than usual a survey of roadkill was undertaken between April and June 2020. The survey will be replicated during the same period in 2021 when visitors are back and there is high tourist traffic.

The survey was undertaken by driving with a spotter along three, 10km stretches of road, on the Kakadu Highway, Arnhem Highway and Oenpelli Road. Data was collected three times a week over two months. For each roadkill spotted data was collected on species, environmental characteristics (vegetation, weather, fire history, proximity to closest water crossing), position on road and road characteristics (surface, straight or bend, speed limit), condition of roadkill, observations of scavengers, and photos and measurements were also taken. Four traffic counters that already occur within the park provided the data on traffic levels.

A total of 57 roadkill sightings were made over 24 survey days across the three sites. The greatest proportion were found on the Arnhem Highway (68%), with 21% on Oenpelli Road and 11% on the Kakadu Highway. The vertebrate group mostly impacted by vehicle strike were amphibians (39%), followed by mammals (37%), birds (16%) and reptiles (9%). The species most often found was the agile wallaby (32%) and the cane toad (19%). Kites were observed scavenging from 37% of roadkill sightings.

After the follow-up survey in 2021, we will be able to compare the results from the two traffic scenarios (low and high tourist traffic) and gain a greater understanding of the impacts of tourist vehicles on the vertebrate species of Kakadu. Parks Australia staff undertaking roadkill survey.

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