Extract from ABC News
Seqwater senior scientist David Roberts is working to help hungry lungfish. (Supplied: Seqwater)
Researchers hope they have found a way for a fascinating living fossil to breed in the Brisbane River again.
But its insatiable hunger is making the task harder.
Believed to be the closest living fish relative to humans, the Australian lungfish has remained anatomically unchanged for more than 100 million years.
Granddad was a Queensland lungfish that died at the age of 109 at the Shedd Aquarium in the United States. (Kenneth Lu, Granddad, CC BY 2.0 DEED)
Listed as vulnerable, the threatened species is a remarkable survivor with a unique single lung that allows it to surface, breathe air, and process oxygen through its gills.
"We know they live a long time, in the wild probably about 80 to 90 years," Seqwater senior scientist David Roberts said.
"But in captivity, we believe these fish could live 100-plus years."
Dam disruption
Luckily, that longevity has given researchers time to solve a serious problem created when the Brisbane River was dammed to secure water for south-east Queensland.
Wivenhoe Dam is in south-east Queensland. (ABC News)
They discovered that downstream of the 40-year-old Wivenhoe Dam, there were plenty of older lungfish, but very few juveniles.
The breed critically depends on Vallisneria, commonly known as eelgrass or ribbon grass, for both food and nursery habitat.
But the aquatic plant was yet to recover after it was scoured from the riverbed during Brisbane's devastating 2011 floods.
Vallisneria can easily be cultivated. (Supplied: Colin Burke)
Dr Roberts said while the omnivores survived in the river by eating clams, crayfish, and other invertebrates, the loss of the plant meant the lungfish had no way to hide their precious eggs when breeding.
"So, for three weeks, this egg is just sitting somewhere, unprotected, open to consumption by all sorts of critters," Dr Roberts said.
"And then after they hatch, the little larva is pretty much defenceless for probably the first six months of its life."
It was a different story upstream of Wivenhoe Dam.
Juvenile lungfish have been very hard to find downstream of Wivenhoe Dam. (Supplied: David Roberts, Seqwater)
In Queensland's Mary and Burnett rivers, where lungfish are endemic, researchers said Vallisneria beds typically recovered within three years of a major flood.
"There were always plants drifting down the river from other locations, little pockets of plants that are protected from the flood or in feeder creeks or side creeks," Dr Roberts said.
"They produce plants and seeds, and they float down and re-establish the river."
Water pours from a floodgate at Wivenhoe Dam, north-west of Brisbane, days after the 2011 flood. (ABC News: Kerrin Binnie)
But Wivenhoe Dam disrupted the plant's recovery and the lungfish's ability to breed.
"Unfortunately, below the dam, there aren't many feeder streams, so there are no real pockets of plants around to start," Dr Roberts said.
"The dam is just unfortunately too large for these small plants that are floating down the river to make their way all the way through the dam, downstream."
Lungfish in the Brisbane River. (Supplied: Colin Burke)
Trial and error
The researchers' initial attempts to grow the eelgrass in six fenced enclosures, 750 metres downstream of the dam, were very successful.
Aquatic plants raised in enclosures couldn't grow fast enough for the hungry lungfish. (Supplied: Colin Burke)
But the torpedo-shaped, large-scaled lungfish broke through the barriers at every opportunity.
In one flood event, Dr Roberts said a lungfish raid on the cultivated eelgrass was so intense that researchers were tripping over them.
"They were jumping out and splashing around … just sitting there, 'Munch, munch, munch' on our plants."
The hungry lungfish ate all of the plants in the enclosure. (Supplied: Colin Burke)
They were uprooted, and the new habitat was decimated when the fences were removed.
Native turtles and invasive fish species, including carp, tilapia, and goldfish, joined the feast.
'Feedback loop'
PhD candidate Colin Burke, from Griffith University's Australian Rivers Institute, is leading the project to help restore the lungfish habitat.
Colin Burke is researching how to restore lungfish habitat. (Supplied: Colin Burke)
But he said the lungfish's insatiable hunger was working against the very plant it needed to survive.
Last summer, he trialled a simple new approach that was cheaper and far less labour-intensive.
Instead of fenced buffets of eelgrass, he provided many tiny dining spots, where the lungfish could graze.
Chucking it out
At five different shallow spots along a 1.5-kilometre stretch of the Brisbane River, he threw out large lumps of cultivated eelgrass and another edible aquatic plant.
Colin Burke releasing aquatic plants for lungfish. (Supplied: Colin Burke)
"We've been finding little, tiny beds establishing along the riverbank, which is quite good," Mr Burke said.
"I think this method spreads out the potential grazing opportunities.
"So it's not just one big patch that lungfish and other fish and aquatic creatures can just circle and linger at for a long time."
The scattered Vallisneria is taking hold in the shallows. (Supplied: Colin Burke)
The PhD student has also driven stakes into the river to provide Vallisneria with more opportunities to catch and establish.
Mr Burke believes it is the first attempt to restore aquatic plants this way, and once his second paper is published, he hopes to repeat the experiment further downstream.
"When you see the little plants pop up, it's quite exciting to be honest."
A stake provided a place for the Vallisneria to grow. (Supplied: Colin Burke)
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