For nine hours, my colleague Michael Shackleton and I held onto our scooters for dear life while being slapped in the face by spiked jungle plants in the mountains of Cambodia. We only disembarked either to help push a scooter up a slippery jungle path or to stop it from sliding down one.
With our gear loaded up on nine scooters – 200 metres of fishing nets, two inflatable kayaks, food for five days, hammocks, preservation gear for collection of DNA, and other assorted scientific instruments – we at last arrived at one of the few remaining sites known to harbour the critically endangered Siamese crocodiles.
The Siamese crocodile once lived in Southeast Asian freshwater rivers from Indonesia to Myanmar. But now, fewer than 1000 breeding individuals remain.
In fact, during the 1990s the species was thought to be completely extinct in the wild. Then, in 2000, scientists from Fauna and Flora International found a tiny population in the remote Cardamom Mountains region of Cambodia.
We travelled to this remote wilderness in 2017 to determine habitat suitability for the reintroduction of captive-bred juvenile Siamese crocodiles. We wanted to understand the food web there to see whether it contains enough fish to sustain the young crocs.
Our journey would not have been possible without the help of Community Crocodile Wardens – local community members who patrol the jungle sanctuaries for threats and record crocodile presence. Wardens also conduct crocodile surveys further afield to discover new populations or to identify new areas of potential suitable crocodile habitat for juvenile releases.
Our recent study found to ensure the species survives, reintroduction locations must be protected from fishing pressure – both from a food supply perspective, but also from risk of entanglement in nets.
A species in decline
When we arrived at our site, northwest of the village of Thmor Bang, our day was capped by what we came to know as the standard evening downpour, despite assurances that we had, in fact, timed our trip for the dry season.
Kayaks were inflated, nets set, and sampling was underway. This proved laborious – to ensure crocodiles didn’t drown, we couldn’t leave nets unattended in the water overnight, but instead checked them every hour until morning.
Siamese crocodiles are generally not aggressive to humans, but they come into conflict with people when caught in fishing nets.
This often leads to the crocodile drowning and the fishing net being ruined. It’s a disaster on both counts, because fish is the only source of protein for many local communities in Cambodia.
Like many other apex predators around the world, the Siamese crocodile is also in decline because of habitat destruction and poaching for their skins.
Their potential large size and generally placid nature means they are highly prized by crocodile farmers who use the skins for handbags and footwear. Crocodile farmers also often hybridise the Siamese crocodiles with other non-native crocodile species.
This means programs for Siamese crocodile reintroduction and breeding must carefully genetically screen all young crocodiles bred in captivity to make sure they’re not actually hybrids, so the “genetically pure” wild populations can remain.
Finding fish bones in croc poo
Despite a pretty good understanding of captive Siamese crocodile behaviour and biology, very little is known about Siamese crocodiles in the wild, such as what they eat or how much food they need to raise an egg to adulthood.
Our only reliable indication of diet comes from scats (crocodile poo or “shit of croc” as we came to call it) collected along the river banks inhabited by remnant populations.
Carefully collected poo samples containing scales and bones tell us fish and snakes make up a significant proportion of the Siamese crocodile diet.
But the shrouded, mystical, extremely remote and virtually inaccessible jungle in the Cardamom Mountains has ensured we know next to nothing about fish communities within habitats set for the release of captive crocodile. And this information is particularly important for prioritising release locations for captive bred juveniles.
We spent four days sampling fish communities and then repeated the process at two other equally remote locations within the Cardamoms, requiring two days travel between each.
We saw groups of gibbons moving through the forest and macaques climbing down from trees to drink at the river. But at last we spotted a wild Siamese crocodile after dark, swimming in our morning bathing pool, on our second-last day.
Ultimately, we distinguished 13 species of fish from the Cardamom Mountains, confirming the presence of two previously unconfirmed species groups for the region.
What’s more, we found fish density was highest in areas with more Siamese crocodiles, and lowest in areas with more human fishing pressure.
Understanding the food web of crocodile reintroduction sites is important, because conservation managers need to understand the ecological carrying capacity of the system – the number of individual crocodiles that can be supported in a given habitat. Learning this is especially important when historical information does not exist.
Preservation of fish stocks within Siamese crocodile habitats is critical for survival of the species. But a key challenge for natural resource managers of the Cardamom Mountains is balancing crocodile density with local fishing necessity, and to do this, we need more information on Siamese crocodile biology.
Planning a trip to the tropics? You might end up bringing home more than just a tan and a towel.
Our latest research looked at mosquitoes that travel as secret stowaways on flights returning to Australia and New Zealand from popular holiday destinations.
We found mosquito stowaways mostly enter Australia from Southeast Asia, and enter New Zealand from the Pacific Islands. Worse still, most of these stowaways are resistant to a wide range of insecticides, and could spread disease and be difficult to control in their new homes.
Undetected insects and other small creatures are transported by accident when people travel, and can cause enormous damage when they invade new locations.
Of all stowaway species, few have been as destructive as mosquitoes. Over the past 500 years, mosquitoes such as the yellow fever mosquito (Aedes aegypti) and Asian tiger mosquito (Aedes albopictus) have spread throughout the world’s tropical and subtropical regions.
Dengue spread by Aedes aegypti mosquitoes now affects tens to hundreds of millions of people every year.
Explainer: what is dengue fever?
Adults in your luggage
You probably won’t see Aedes mosquitoes buzzing about the cabin on your next inbound flight from the tropics. They are usually transported with cargo, either as adults or occasionally as eggs (that can hatch once in contact with water).
It only takes a few Aedes stowaways to start a new invasion. In Australia, they’ve been caught at international airports and seaports, and in recent years there has been a large increase in detections.
In our new paper, we set out to determine where stowaway Aedes aegypti collected in Australia and New Zealand were coming from. This hasn’t previously been possible.
Usually, mosquitoes are only collected after they have “disembarked” from their boat or plane. Government authorities monitor these stowaways by setting traps around airports or seaports that can capture adult mosquitoes. Using this method alone, they’re not able to tell which plane they came on.
But our approach added another layer: we looked at the DNA of collected mosquitoes. We knew from our previous work that the DNA from any two mosquitoes from the same location (such as Vietnam, for example) would be more similar than the DNA from two mosquitoes from different locations (such as Vietnam and Brazil).
So we built a DNA reference databank of Aedes aegypti collected from around the world, and compared the DNA of the Aedes aegypti stowaways to this reference databank. We could then work out whether a stowaway mosquito came from a particular location.
We identified the country of origin of most of the Aedes aegypti stowaways. The majority of these mosquitoes detected in Australia are likely to have come from flights originating in Bali.
Now we can work with these countries to build smarter systems for stopping the movement of stowaways.
As the project continues, we will keep adding new collections of Aedes aegypti to our reference databank. This will make it easier to identify the origin of future stowaways.
New mosquitoes are a problem
As Aedes aegypti has existed in Australia since the 19th century, the value of this research may seem hard to grasp. Why worry about invasions by a species that’s already here? There are two key reasons.
Currently, Aedes aegypti is only found in northern Australia. It is not found in any of Australia’s capital cities where the majority of Australians live. If Aedes aegypti established a population in a capital city, such as Brisbane, there would be more chance of the dengue virus being spread in Australia.
The other key reason is because of insecticide resistance. In places where people use lots of insecticide to control Aedes aegypti, the mosquitoes develop resistance to these chemicals. This resistance generally comes from one or more DNA mutations, which are passed from parents to their offspring.
Importantly, none of these mutations are currently found in Australian Aedes aegpyti. The danger is that mosquitoes from overseas could introduce these resistance mutations into Australian Aedes aegpyti populations. This would make it harder to control them with insecticides if there is a dengue outbreak in the future.
In our study, we found that every Aedes aegpyti stowaway that had come from overseas had at least one insecticide resistance mutation. Most mosquitoes had multiple mutations, which should make them resistant to multiple types of insecticides. Ironically, these include the same types of insecticides used on planes to stop the movement of stowaways.
Other species to watch
We can now start tracking other stowaway species using the same methods. The Asian tiger mosquito (Aedes albopictus) hasn’t been found on mainland Australia, but has invaded the Torres Strait Islands and may reach the Cape York Peninsula soon.
Worse still, it is even better than Aedes aegypti at stowing away, as Aedes albopictus eggs can handle a wider range of temperatures.
A future invasion of Aedes albopictus could take place through an airport or seaport in any major Australian city. Although it is not as effective as Aedes aegypti at spreading dengue, this mosquito is aggressive and has a painful bite. This has given it the nickname “the barbecue stopper”.
Beyond mosquitoes, our DNA-based approach can also be applied to other pests. This should be particularly important for protecting Australia’s A$45 billion dollar agricultural export market as international movement of people and goods continues to increase.
Tom Schmidt, Research fellow, University of Melbourne; Andrew Weeks, Senior Research Fellow, University of Melbourne, and Ary Hoffmann, Professor, School of BioSciences and Bio21 Institute, University of Melbourne
Australians love to complain about weather forecasts, but compared with some other parts of the world ours are impressively accurate. Our large, mostly flat continent surrounded by oceans makes modelling Australia’s weather and climate relatively straightforward.
The same cannot be said about our neighbours to the north.
For Southeast Asian countries such as Indonesia and Papua New Guinea – which we collectively refer to as the “Maritime Continent” – things are a lot more complicated. With their mountainous terrain and islands of different shapes and sizes, it’s much harder to model the weather and climate of this region.
The models we use to make the most of our climate projections have to simulate the climate for many decades to provide us with useful information. To run such long simulations we have to compromise on resolution; even state-of-the-art global climate models divide the world into grid boxes more than 100km across. The Maritime Continent doesn’t come out too well at these resolutions.
It’s unfortunate the Maritime Continent’s weather and climate are so tricky to simulate on long time scales. Due to its location right on the Equator and between the Indian and Pacific Oceans, this region has a defining influence on the global climate, being a major source of heat and water vapour to the atmosphere. If we don’t simulate the climate over the Maritime Continent well, we can get errors appearing on the global scale.
Besides that, the Maritime Continent is also home to hundreds of millions of people, and includes major cities such as Jakarta and Singapore. We need our weather and climate models to simulate the processes behind the severe storms, heatwaves, and droughts that these cities and the broader region experience. Accurate weather forecasts, seasonal outlooks and climate projections require models to simulate the atmosphere over the Maritime Continent well.
In our new study, published in Geophysical Research Letters, we show that many state-of-the-art global climate models struggle to simulate the climate of the Maritime Continent. But fortunately, a higher-resolution model captures more of the major processes in this area.
The benefits of high resolution
Like in Australia, much of the Maritime Continent region is wetter during La Niña seasons and drier in El Niño, although for some western coasts and Sumatra it’s the other way round. Many global climate models fail to reflect accurately this rainfall response to El Niño and La Niña.
We found that for climate models to do a good job in capturing the year-to-year variability in rainfall over the Maritime Continent, they need to do a few things well. Specifically, they need to represent accurately the amount of moisture held in the atmosphere, as well as the pattern of winds in the region. This gives the right pattern of rainfall response to El Niño and La Niña.
Our higher-resolution regional climate model does a much better job at simulating the Maritime Continent’s rainfall patterns than many of the global models we looked at. As the region has such a complex landscape, global models simply cannot capture enough detail on all the different processes between the land and the ocean, and the coasts and the mountains. But higher-resolution regional models can.
As the Maritime Continent is so important for the global climate but so difficult to model, there is a concerted effort to improve our models and to get more atmospheric observations across the region.
International projects such as the Years of the Maritime Continent are taking place, with millions of dollars and dozens of researchers working on improving our understanding of the region’s weather and climate.
Ultimately, we hope that through better, higher-resolution model simulations, we can capture the processes behind the Maritime Continent’s weather and climate much more accurately. This should lead to better climate projections and seasonal forecasts not only for the region, but for the world as a whole.
This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to firstname.lastname@example.org
In Japan, many people wear face masks – is that to prevent the wearer getting the infection, or is the wearer already infected and protecting those around? Is the mask useful in protecting against viruses or bacteria? – Petrina, Greenwich
Thanks for your question, Petrina. You’re right, in countries like Japan and China, facemask use in the community is widespread – much more so than in Western cultures. People wear them to protect the respiratory tract from pollution and infection, and to prevent the spread of any pathogens they might be carrying.
Whether this works depends on the type of mask.
There are three supposed ways a mask can provide protection: by providing a physical barrier (which prevents splashes and sprays), by filtering the particles (blocking particles of a certain size from entering the respiratory tract), and by fitting around the face to prevent leakage of air around the sides.
Some mask makers have also gone the extra step of using antimicrobials and claim to kill bugs on the surface of the mask, but these haven’t been tested to see if they provide any benefit.
Healthcare workers have been using cloth masks (made of cotton or other materials and with ties to secure them at the back) while caring for patients since the late 19th century to protect from various respiratory infections such as diphtheria, scarlet fever, measles, pandemic influenza, pneumonic plague and tuberculosis.
During the mid 20th century, disposable surgical facemasks (similar in look to the cloth masks but made of paper) were developed. Surgical masks were developed to prevent the surgeon from contaminating the wound during surgery, but studies have not proven they help.
These were followed by respirators, which vary in shape and material but are designed to fit around the face and filter particles. Respirators are designed specifically to protect the respiratory tract from inhaled germs. There are many types, which may be reusable or disposable.
People must undergo fit-testing to ensure respirators are correctly fitted, with a good seal around the face. Unlike masks, respirators are subject to certification and regulation, and are proven to protect against respiratory infection.
Surgical masks are unregulated for filtration and do not fit around the face, and the evidence for their use is less convincing. In a community study, families with a sick child who wore such a mask were less likely to get sick if they also wore a mask, but many family members didn’t wear their masks all the time.
In a university setting, students were protected from sick classmates if they wore the mask within 36 hours of their classmate getting sick.
In many low income countries, the cost of even paper surgical masks is prohibitive, so cloth masks are used, washed and re-used. But these don’t protect against infection, and may even increase the risk of infection.
Prevention of infection vs source control
Masks can be used to protect healthy people (such as nurses and doctors) from exposure to infection, but are also used by sick people (such as a TB patient) to prevent spread of infections to others (called “source control”). There is less research on this use than on the use of masks by well people. The efficacy of source control is unknown.
Do masks work?
It’s long been thought surgical masks protect from transmission of pathogens, which spread through the air on large, short-range droplets, while respirators protect against much smaller, airborne particles, which may remain suspended in the air for several hours and transmit infection over long distances. So most guidelines recommend a mask for droplet transmitting infections (such as influenza) and a respirator for airborne infections (such as TB and measles).
But we’ve shown respirators protect better than masks even against droplet-spread infections. And the longstanding belief that infections neatly fit into either droplet or airborne transmission is not correct. Respiratory transmission of infections is more complex than this.
To say whether masks work, we have to specify whether we’re talking about a respirator, a surgical mask or a cloth mask.
The respirators are the Rolls Royce option and do protect, and this is a tool for frontline health workers facing epidemics of known and unknown infections. Surgical masks probably also protect but to a lesser extent. But there’s no evidence cloth masks will protect against invading or escaping bugs.