A tiny frog with a big problem has sparked a mountain-top rescue mission in Far North Queensland.

Conservationists are working in dense rainforest near the summit of Mt Lewis, north of Cairns, to save the critically endangered mountain-top nursery-frog which is facing two challenges – feral pigs and a changing climate.

The frog is roughly the size of a thumbnail and it lays eggs under leaf litter. It is only found in high-altitude cloud forests in Mt Lewis National Park near Julatten.

Feral pigs a major threat

Terrain NRM’s Dr Andrew Dennis says feral pig numbers appear to be increasing above 1,100 metres, based on the amount of disturbance being seen.

“Over time they’ve slowly migrated upwards from the low altitude areas of the mountain,’’ he said.

“In mountain-top nursery frog breeding sites up near the top of Mt Lewis, pigs are now digging up the ground and leaving bare soil where there was leaf litter and tree seedlings, and we’ve observed them digging in the roots of the Linospadix apetiolatus palms.

“These tiny frogs breed in leaf litter. The males call from the palms, to project their voices to females. Eggs are laid in the leaf litter on the palm leaves or the ground. Where it’s deep, it also holds a lot of food for them. But with pig disturbances, they are losing both breeding and feeding zones.”

Installing pig-exclosure fencing

One of the answers is pig exclosure fencing. Terrain NRM has been working with Western Yalanji Traditional Owners and Gulf Savannah NRM to erect fences around 10 breeding sites in dense cloud forest near the top of the mountain. Now they’re also working with the Queensland Parks and Wildlife Service and James Cook University researchers, using frog-call monitors and regular habitat assessments to monitor these sites and rare frogs.

“Breeding season is generally from October-November to March,’’ Dr Dennis said.

“We have 10 fenced sites that exclude pigs and 10 control plots that aren’t fenced and they’re all about 60 metres apart so that calls from frogs at one plot shouldn’t be heard at another.

Audio recorders for population monitoring

“We have audio recorders at each site to monitor calling activity and we’re also regularly monitoring the habitat, measuring things like seedling and leaf litter density and any recovery of the Linospadix apetiolatus palms.

“Pigs are churning up significant areas of this fragile habitat. We are measuring this as part of the project. On a wider scale, they’re also a weed and water quality threat to a highly biodiverse area of the Wet Tropics at the headwaters of the Mitchell and Mossman River systems.”

Climate change a threat to frogs high up on Mt Lewis

At least five frog species have disappeared from the top of Mt Lewis in the past few decades, with three of them likely extinct worldwide. Dr Dennis said a fungal disease had been the main cause of their demise, but climate changes pose another threat to species at the high altitudes of ranges like Mt Lewis.

“I’ve been visiting this region for well over 50 years. Walking in the cloud forest and around the creeks, it used to be noisy with frog calls day and night. Now it’s noticeably a lot quieter.”

Frog’s trill tells a sad story

The mountain-top nursery frog’s trill is also diminishing.

“Calls were detected by researchers in 2003 at 1,100 metres. But 20 years later, in 2023, there were no calls at 1,100 metres. They were detected at 1,200 metres and above.

New fishways are helping fish species, including barramundi and mangrove jack, to breed up in North Queensland waterways.

Six fishways built between Tully and Crystal Creek near Paluma over the last year have removed barriers for juvenile fish. Together, they’ve opened up more than 100 kilometres of creek and river systems – and recent surveys at these sites have shown they are fish highways.

Fish highways – 16 native species including barra, tarpon

More than 1000 fish were recorded moving through one of the fishways – at Insulator Creek north of Townsville – in one day. And in more recent surveys, over 4500 fish were caught and released during monitoring work at four rock ramp fishways.

“Sixteen native species, including juvenile barramundi, empire gudgeon, rainbow fish, tarpon and long-finned eels, were recorded,’’ Terrain NRM’s Deb Bass said.

“Of the 80+ species of native fish we have in the Wet Tropics region, up to half need to move between salt and freshwater habitats to complete their lifecycles. Barriers like weirs, pipes, culvert crossings and weed chokes can stop these species from thriving.

“In recent surveys at our fishways, eight of the 16 native species recorded are species that need that movement – from their beginnings in saltwater to safer freshwater nursery grounds as juveniles and then back downstream to the saltwater to breed as adults. So we can see the fishways are providing access for these species, from barramundi and mangrove jack to shrimps.”

A series of underwater stairs for fish

Terrain NRM has been working with OzFish Unlimited, Catchment Solutions and Australasian Fish Passage Services on the ‘Fish Homes and Highways’ project, which is funded by the Australian Government’s Reef Trust. Fishways are a relatively new solution in the region – a series of underwater stairs for fish, with deep pools between each one for resting.

Catchment Solutions fishery ecologist Matt Moore said rocks were placed strategically, sometimes in S-bend and sometimes a straight line, to achieve the right gradient to create a slower flow while also being able to withstand floods.

“To pull in our monitoring traps and see all the fish – a lot goes into the design of these structures, so we love seeing a result like this,’’ he said.

New ‘nursery slot’ for super small juveniles 

A ‘nursery slot’ is a new feature, trialled in one of the fishways, to help super small juveniles move upstream.

“It needs 20mm or less of water going through it to create the right conditions for weaker-swimming juvenile fish,” Matt said. “We recently recorded the smallest snakehead gudgeon ever documented in Australian fishway studies travelling through the slot. It was 16mm long.”

The critically endangered mountain-top nursery frog has jumped into the spotlight as a new project starts, aimed at improving its chances of survival.

The mountain-top nursery frog is only found near Mt Lewis, west of Port Douglas.

Terrain NRM secured funding this week through the Australian Government’s Saving Native Species (Priority Species) Grants for a project focused on protecting the rare frog’s breeding sites at the heights of Mt Lewis National Park.

Reducing threats to mountain-top nursery frogs

The project aims to reduce threats to the survival of the mountain top nursery frog and will be delivered by Terrain in partnership with Western Yalanji traditional owners, James Cook University researchers, Gulf Savannah NRM and the Queensland Parks and Wildlife Service.

Project leader Dr Andrew Dennis said feral pigs were a major threat and pig exclusion fencing would be installed around known frog breeding sites. Pig control measures would also begin soon, as well as species monitoring work.

“These frogs are only found in dense, small-leafed, or microphyll rainforest at altitudes above 1100 metres – they’re considered to be one of the most range-restricted frog species in Australia,” Dr Dennis said. “Because of this they’re extremely vulnerable to the effects of climate change from warming to changes in rainfall and cloud distribution.

Focus on feral pigs

“Feral pigs are another big threat, and pigs are increasing in numbers at high altitudes and disturbing and in some cases destroying the small palms and woody debris that are critical habitat for the mountain top nursery frog.

“Western Yalanji traditional owners will help monitor exclosure fencing and with surveying the feral pig damage on Mt Lewis, and we’ll work with Queensland Parks and Wildlife rangers on the most effective control measures.

“About 2000 square metres of frog breeding habitat will be fenced off.

“We will also be partnering with James Cook University on research to monitor protected and unprotected habitat, looking at the breeding success of mountain top nursery frogs, the amount of woody debris and the numbers of small palm trees (Linospadix apetiolatus) that they live in and near.

More help is on its way for the critically endangered Kuranda tree frog.

Community organisation Kuranda Envirocare is launching a new project, surveying more creeks and training extra volunteers thanks to a recently announced Engaging Science Grant from the Queensland Government.

The new initiatives come on the tenth anniversary of the organisation’s ‘Frog-Friendly Waterways’ citizen science program, and at a time when the Kuranda tree frog is facing ongoing threats from urbanisation and related changes to creek hydrology.

Monitoring with acoustic recorders

Project coordinator Edward Bell said acoustic recorders would be used to bring more creeks into the monitoring program.

“These will enable us to survey larger and more remote areas, ensuring we have the best available information on where the Kuranda tree frog is surviving,’’ he said.

About the Kuranda tree frog

The Kuranda tree frog, or Litoria myola, is only known to live in a handful of creeks that flow into the Barron River. Discovered in 2007, its biggest threats are habitat clearing along creek lines and hydrological disturbances to creek beds.

Kuranda Envirocare president Cathy Retter said volunteers had been regularly monitoring frog populations for nine years with researchers from James Cook University, and also working with landholders to revegetate creek lines in key areas for the species.

Revegetation work

“More than five kilometres of creek and riverbanks have been successfully revegetated, and this will continue into the future,’’ she said.

“With our new project, we are looking forward to working with more volunteers and training them in the use of detectors and water quality monitoring equipment, and in analysis of acoustic data.”