There are doubts the Noah’s Ark plan for the Lower Darling will be enough to prevent more mass fish kills

This article is more than 1 year old

This article is more than 1 year old

Faced with a looming ferocious summer with little rain forecast, the New South Wales government has embarked on a Noah’s Ark type operation to move native fish from the Lower Darling – part of Australia’s most significant river system – to safe havens before high temperatures return to the already stressed river basin.

Researchers have warned of other alarming ecological signs that the Lower Darling River – part of the giant Murray-Darling Basin – is in a dire state, following last summer’s mass fish kills.

Professor Fran Sheldon, from Griffith University’s Australian Rivers Institute, said only one surviving colony of river mussels had been found along the river and there were signs that river red gums were under severe stress.

“If the river red gums die, and some are hundreds of years old, there will be a domino effect. Banks will collapse, there will be massive erosion and it will send sediments down the river.”

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“These sort of ecological collapses are much harder and expensive to reverse,” she warned.

The New South Wales government announced a $10m rescue package last week to mitigate the effects of the river crisis on native fish this summer.

The NSW agriculture minister, Adam Marshall, said the unprecedented action would provide “a lifeline for key native species ahead of an expected summer of horror fish kills”.

“We’re staring down the barrel of a potential fish Armageddon, which is why we’re wasting little time rolling out this unprecedented action,” Marshall said.

“By starting this operation today we’re getting on the front foot while we still have the chance to rescue and relocate as many fish as possible.”

Last December and January fish began dying in their hundreds of thousands in the far west of the state at Menindee, leaving weirs and waterholes carpeted with dead fish. While fish deaths have occurred in the past, the scale was unprecedented and stunned Australians.

Several scientific reports said the lack of flow in the river due to the drought and exacerbated by irrigation upstream were to blame. When temperatures soared to over 40C and were followed by a cool change, the water in the pools stratified, leading to deoxygenation of the deeper water, killing fish.

But there are already doubts about how effective the $10m program will be.

The unprecedented operation aims to move as many fish as possible from 15 to 20 priority waterholes in a two-week period, including Murray cod, some of which are at least 25 years old, golden perch and other rare species.

Boats with electrostatic fishing equipment will be used to stun the fish in weir pools and waterholes along the Darling at Menindee, where they will scooped up and loaded into special climate-controlled transport to a section of the Darling further south, near Wentworth, where the river joins the Murray, which is still flowing.

Department of Primary Industries fisheries scientists are targeting fish contained within drying pools that are not expected to last through the summer.

“By moving these fish, such as Murray cod and golden perch, we’re providing the best possible chance of survival,” Marshall said.

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But the government has not said how many fish it will move. One source told the Guardian it was hoped it would be in the hundreds. This is just a fraction of the population of the river and will not prevent the likelihood of further mass fish deaths during the coming summer.

“It’s a photo-op rather than a real deal,” said a Menindee local, Graeme McCrabb, who has become a spokesman for the local community on the lower Darling.

“There would be 10,000 cod between Weir 32 [at Menindee] and the Murray,” he said. “And silver perch, listed as a vulnerable species, are difficult to catch with electro fishing.”

“If Lake Wetherill goes, there will be even more fish die than last year,” McCrabb warned.

A program last summer to install aerators in larger waterholes near Menindee, which aimed to stir the water and restore oxygen, was only marginally successful due to the size of the pools and the vast length of the river.

Meanwhile, the NSW government appears to be in denial about possible causes of the ecological catastrophe last summer. The water minister, Melinda Pavey, has criticised her own independent adviser, the NSW Natural Resources Commission, which said extractions by irrigators upstream may have led to the Lower Darling being pushed into hydrological drought three years earlier than it otherwise would have been.

The commission has called for an urgent revision of the rules that allow irrigators to continue to extract from the river when flows are very low. It wants the threshold when irrigators must cease to take water from the river to be raised, along with other rule changes.

“The NRC report was one of a number that has given advice on this issue,” said Sheldon, who contributed to the report.

“It’s a contentious issue. We just raised the question: have [the extraction rules] influenced the conditions that have led to the catastrophic drying of the Barwon-Darling?”

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“If the answer is that extractions did contribute, then the answer is straightforward: we need to change the rules.

“If they didn’t, then the answer is a whole lot more complex. We need to understand what is really going on.”

“The fish rescue program will preserve some genetic diversity, but the government also needs to monitor the surrounding ecosystems, as [returning] fish would not survive if mussels and other invertebrates are lost,” she said.

The government said the fish would be able to migrate back up the 500km of the Darling when the drought ended.

“When flows do return to normal, the fish will be able to migrate to their ‘homes’ back upstream, without the need for additional intervention,” Marshall said.

• On 10 September 2019 this article was amended. A previous version said water in pools “striated” when “stratified” was meant.