An innovative trial to turn a noxious fish into fertiliser could help ancient and endangered species flourish in one of Queensland’s most diverse river systems.
The Mary River stretches 291 kilometres from the Sunshine Coast to the Great Sandy Strait at Hervey Bay and uniquely flows south to north.
But below the surface is its most notable feature: a unique group of species that conservationists say are “scientifically important, totemic and iconic”.
The lungfish first appeared in the fossil record 380 million years ago. (ABC News: Chris Gillette)
It includes rare species such as the bum-breathing Mary River turtle, the Mary River cod, the critically endangered white-throated snapping turtle and the Australian lungfish, often called a living fossil.
For the first time, researchers have joined forces with conservationists and traditional owners to embark on an 18-month detailed study of the river’s species.
Burnett Mary Regional Group (BMRG) led the study and chief executive Tom Espinoza said it delivered alarming results.
Tom Espinoza says the fish are competing for habitat with native species. (ABC News: Christopher Gillette)
“In the past there hasn’t been a really comprehensive stocktake of where our threatened species are, but just as important is where our threatened species aren’t,” Mr Espinoza said.
The study found in just two years the invasive tilapia found in the lower reaches of the catchment had “proliferated and expanded” through the whole area.
“They’re competing for habitat, they’re competing for food, they’re sometimes predating on the smaller size classes and juveniles of our threatened species,” Mr Espinoza said.
Tilapia are threatening endangered species and the Australian lungfish. (ABC News: Christopher Gillette)
The research used a new method called environmental DNA (eDNA) to collect data, combined with traditional sampling.
“You take a water sample and it tells you everything that lives in a water hole, river or lake,” Mr Espinoza said.
Traditional owners included the Kabi Kabi people, who journeyed the entire length of the river on canoe as part of the research.
As part of the study, conservationists, researchers and traditional owners canoed the entire length of the river. (ABC News: Curtis Rodda)
Kabi Kabi People’s Aboriginal Corporation director Kerry Jones said projects like this helped to bring traditional owners back onto country.
“It gave us an insight on what’s actually happening,” Mr Jones said.
“But the frequency and how quick it’s happening was an eye-opener for us.”
Turning the tide on tilapia
Tilapia were introduced into Australia in the 1970s as an ornamental fish and are listed as a restricted noxious fish under biosecurity legislation.
They cannot be kept, fed, given away, sold or released into the environment and should be destroyed and disposed of immediately if caught.
The invasive tilapia fish is found in 26 of Queensland’s 67 catchments, including the Mary River. (Supplied)
Reece Pianta from the Invasive Species Council said tilapia’s success as an invasive fish meant eradication was not possible, and the species could now be found in 26 of Queensland’s 67 catchments.
“It [managing tilapia] becomes about mitigating their effects on native fish and the natural environment,” Mr Pianta said.
BMRG hopes a technique used on the Murray-Darling Basin to turn carp into fertiliser could be the answer to protecting the Mary River.
Mr Espinoza said the group was seeking a special licence for traditional owners to be able to harvest the no-take fish and turn them into fertiliser that would be used within a native plant nursery.
The study of the Mary River found the invasive tilapia has infiltrated the entire river system. (ABC News: Christopher Gillette)
“We’re interested in purchasing those native plants to undertake all the revegetation and other habitat restoration activities that we do in the catchment,” he said.
It is the short-term plan while conservationists work on building native species’ numbers.
“If we can support populations of the Mary River cod, they’ll quickly get to a size where they can eat the tilapia,” Mr Espinoza said.
Mr Pianta supported the idea.
“Something like this can be a long-lasting project that could actually achieve some local control of the tilapia population in the river,” he said.
