A leap of progress for the Red-finned Blue-eye

This Threatened Species Day, we take you to the uniquely biodiverse inland arid springs to check in on our favourite fish protagonist. 

In 1925, Eastern Gambusia (Mosquitofish) were introduced to Australia from America in an effort to control mosquitoes.

After decades of dominating their environment, they have forced many species of native fish out of their habitats.  

If you're familiar with Bush Heritage’s work then you're likely familiar with one of these native fish: the Red-finned Blue-eye, a species that has become an unlikely hero in the face of terrifying odds. Listed as critically endangered by the International Union for Conservation of Nature (IUCN), this tiny fish grows to little more than the size of your thumbnail. Its only wild population exists on our Edgbaston Reserve, Bidjara Country, central Queensland.  

For Threatened Species Day, we’re checking in on the fish to find out the latest. 

In an otherwise dry, arid landscape, water from the Great Artesian Basin has travelled up to the surface to create ankle-deep springs and a unique freshwater habitat. Dr. Dean Gilligan took on the role of Freshwater Ecologist for Bush Heritage in 2021 with an enormous challenge ahead: to control gambusia and ensure that the new breeding populations of Red-finned Blue-eyes continue to thrive.  

“When I came on board, my predecessor, Dr Pippa Kern, had done an amazing job reintroducing the species into the springs at Edgbaston through a successful captive breeding program,” said Dean “But the Gambusia are little bullies and present continuous challenges.” 

“They either nip their fins, eat their eggs, eat their larvae, or just exclude them from the preferred vent area of the springs, relegating them to the periphery where the temperatures fluctuate wildly and there are high concentrations of salts and extreme pH, making life very tough for the Blue-eyes.” 

Wherever the gambusia invade, the Blue-eyes are usually gone within 12-18 months.

Before Bush Heritage took responsibility for their conservation, the little fish’s chances were slight at best.

Thanks to a recent Threatened Species Strategy Action Plan grant from the Australian Government, a new and ambitious commitment to establish five new Red-finned Blue-eye populations within 12-months is well underway. The process, built upon and refined from methods developed by previous Bush Heritage Edgbaston ecologists, is complex and labour-intensive and has not been applied on this scale before.

“We are deliberately pushing the envelope, by targeting much larger springs than have been rehabilitated in the past. Because of their scale, they require much more effort to remove the Gambusia and rehabilitate for our Blue-eyes. But the outcome of the extra effort is much more significant. Larger springs have a much higher carrying capacity to support bigger, more sustainable and genetically diverse Blue-eye populations into the future.”     

First, the Bush Heritage team, including Healthy Landscapes Manager, Tony Mayo and a team of volunteers, fence off the entire spring to prevent Gambusia re-invading.

The fences are very low (less than 40 cm high) and made of shade-cloth fine enough to prevent even baby Gambusia from passing through.  

“This part isn’t easy – digging trenches, straining wires, hammering in posts, sometimes through extremely rocky ground, clipping on the shade cloth and then re-burying the trench,” said Dean. 

Another unlikely tool in Dean’s fight for the Red-finned Blue-eye – fire.

“To manage the vegetation, National Fire Program Officer, Alistair Hartley came out in April and helped us burn a few springs to remove the really dense, thick grass thatch and expose all the surface water.”  

Done properly, controlled burning can rejuvenate biodiversity, according to Dean, benefiting the endemic and threatened spring plants being smothered by the grasses and reeds, which in turn benefits the health of the springs. 

“Next step, also relying on volunteers, is to use whipper snippers and brush cutters to trim the last of the vegetation that’s covering the surface of the water – we need to be able to see every puddle that’s left, as Gambusia can inhabit a puddle the size of a boot print,” said Dean.  

“Then we temporarily remove as much of the surface water as we can from the spring using pumps. Luckily, the springs are very resilient to disturbance and they do recover,” he said. 

“The pumping process reduces the final area and volume of water we need to treat – ultimately reducing the impact on the springs. We use an oxygen inhibitor that is harmless to humans and has no impact on non-target species, that blocks the Gambusia’s ability to extract oxygen from the water.

Bush Heritage have gained permission to enact this process under a minor use permit provided by the Australian Pesticides and Veterinary Medicines Authority.  

“We’ve been very successful. We’re five months into the project and we’ve already eradicated Gambusia from three springs. If all goes to plan, we’re determined to achieve three more Gambusia eradications this year. We should have created six new Red-finned Blue-eye populations by 2023.”  

After the springs have been Gambusia-free for six months, they are deemed safe for the reintroduction of Red-finned Blue-eyes. October will mark the first opportunity to do so.

Dean is adamant the work could not have gone ahead if it were not for the volunteer’s contribution.

“Since 2008, we’ve enclosed 17 individual springs, and it’s taken the efforts of nearly 100 volunteers to help us complete the work – each spending at least a week on reserve,” he said.  

Bush Heritage have made extraordinary progress this year, and Dean hopes the pace will continue well into next year.

“Under Bush Heritage Australia’s stewardship”, he said, “we’ve improved the conservation status of Red-finned Blue-eyes. At its worst – only two small populations remained. Before starting the Threatened Species Strategy project, Bush Heritage had increased that number to 12 occupied springs. By the end of the project, we should have established Red-finned Blue-eyes in at least six more – many much larger than any of those created in the past.”

Gambusia - 0, Red-finned Blue-eye – 1 

Not bad news on Threatened Species Day.  

This project received grant funding from the Australian Government.